UV HARVESTING TRANSPARENT PHOTOVOLTAICS
20200343053 ยท 2020-10-29
Assignee
Inventors
Cpc classification
H10K30/82
ELECTRICITY
Y02E10/542
GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
H10K85/50
ELECTRICITY
International classification
Abstract
A transparent photovoltaic cell is provided. The transparent photovoltaic cell includes a first visibly transparent electrode, a visibly transparent active layer including a light absorbing material that has a bandgap greater than or equal to about 2.75 eV, and a second visibly transparent electrode. The active layer is disposed between the first transparent electrode and the second transparent electrode. The transparent photovoltaic cell is visibly transparent.
Claims
1. A transparent photovoltaic cell comprising: a first visibly transparent electrode; a visibly transparent neat active layer comprising a light absorbing material that has a bandgap greater than or equal to about 2.75 eV; and a second visibly transparent electrode, wherein the visibly transparent neat active layer is disposed between the first transparent electrode and the second transparent electrode, and wherein the transparent photovoltaic cell is visibly transparent.
2. The transparent photovoltaic cell according to claim 1, wherein the light absorbing material has a bandgap greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV.
3. The transparent photovoltaic cell according to claim 1, wherein the light absorbing material absorbs ultraviolet (UV) light having a wavelength of less than or equal to about 450 nm.
4. The transparent photovoltaic cell according to claim 1, wherein the light absorbing material is substantially nonabsorbent to light having a wavelength of greater than or equal to about 450 nm.
5. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell has a peak reflectance of greater than about 15% at wavelengths greater than or equal to about 650 nm to less than or equal to about 5000 nm.
6. The transparent photovoltaic cell according to claim 1, wherein the light absorbing material is a halide perovskite.
7. The transparent photovoltaic cell according to claim 6, wherein the halide perovskite comprises halide perovskite nanocrystals.
8. The transparent photovoltaic cell according to claim 6, wherein the halide perovskite has the formula ABX.sub.3, where A is methylammonium (MA), formamidinium (FA), ethanediammonium (EA), iso-propylammonium, dimethylammonium, guanidinium, piperidinium, pyridinium, pyrrolidinium, imidazolium, t-butylammonium, Na, K, Rb, Cs, or a combination thereof; B is Pb, Sn, Ge, Cu, Sr, Ti, Mn, Bi, Zn, or a combination thereof and X is a halide or a combination of halides.
9. (canceled)
10. The transparent photovoltaic cell according to claim 8, wherein the halide perovskite comprises Cl and at least one other halide.
11. The transparent photovoltaic cell according to claim 1, wherein the light absorbing material is a metal halide, a metal nitride, a metal sulfide, a metal selenide, a metal telluride, an alloy thereof, or a combination thereof.
12. The transparent photovoltaic cell according to claim 11, wherein the metal halide comprises at least one of PbI.sub.2, PbCl.sub.2, PbBr.sub.2, PbI.sub.XBr.sub.(1-X), PbI.sub.XCl.sub.(1-X), Snl.sub.2, SnCl.sub.2, SnBr.sub.2, SnI.sub.XBr.sub.(1-X), SnBr.sub.XCl.sub.(1-X), Gel.sub.2, GeCl.sub.2, GeBr.sub.2, GeI.sub.XBr.sub.(1-X), GeI.sub.XCl.sub.(1-X),GeBr.sub.XCl.sub.(1-X), InI.sub.3, InCl.sub.3, InBr.sub.3, TiI.sub.3, TiCl.sub.3, TiBr.sub.3, GaI.sub.3, GaBr.sub.3, GaCl.sub.3, AlCl.sub.3, AlBr.sub.3, AlI.sub.3, A.sub.2TiI.sub.6, A.sub.2TiCl.sub.6, and A.sub.2TiBr.sub.6, where A is an alkali metal, an organic cation, or a combination thereof, and 0x1; the metal nitride comprises at least one of In.sub.(X)Ga.sub.(1-X)N and In.sub.(X)Al.sub.(1-X)N, where 0x1; the metal sulfide comprises ZnS.sub.(X)Se.sub.(1-X), where 0x1; the metal selenide comprises at least one of ZnSe, ZnO.sub.(X)Se.sub.(1-X), and Zn.sub.(X)Mg.sub.(1-X)Se, where 0x1; and the metal telluride comprises at least one of Zn.sub.(X)Mg.sub.(1-X)Te and BeSe.sub.(X)Te.sub.(1-X), where 0x1.
13. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell transmits visible light and has an average visible transparency of greater than or equal to about 45%.
14. The transparent photovoltaic according to claim 1, wherein the transparent photovoltaic cell has a color rendering index of greater than about 80 referenced to an air mass 1.5 global (AM 1.5 G) solar spectrum.
15. The transparent photovoltaic cell according to claim 1, wherein the first visibly transparent electrode is a visibly transparent anode and the second visibly transparent electrode is a visibly transparent cathode.
16. The transparent photovoltaic cell according to claim 1, further comprising: an adjunct layer disposed between the first visibly transparent electrode and the visibly transparent neat active layer, wherein the adjunct layer is an electron transport layer, an electron extraction layer, a hole blocking layer, or a buffer layer.
17. (canceled)
18. (canceled)
19. The transparent photovoltaic cell according to claim 20, wherein the adjunct layer comprises at least one of a fullerene, ZnO, TiO.sub.2, NiO, MoO.sub.3, a conductive nanotube, and a conductive nanoparticle.
20. The transparent photovoltaic cell according to claim 1, further comprising: an adjunct layer disposed between the visibly transparent neat active layer and the second visibly transparent electrode, wherein the adjunct layer is an electron transport layer or an electron extraction layer that provides an ohmic contact between the visibly transparent neat active layer and the second visibly transparent electrode.
21. (canceled)
22. The transparent photovoltaic cell according to claim 1, wherein the second visibly transparent electrode comprises a transparent conducting oxide, a nanowire mesh, conducting oxide nanoparticles, conductive nanotubes, a thin metal layer, or a combination thereof.
23. The transparent photovoltaic cell according to claim 21, wherein the second visibly transparent electrode comprises a thin metal layer comprising silver (Ag) and a conductive layer comprising aluminum tris(8-hydroxyquinolinate) (Alq.sub.3) or indium tin oxide (ITO), wherein the thin metal layer is disposed between the visibly transparent neat active layer and the conductive layer.
24. The transparent photovoltaic cell according to claim 1, further comprising: a visibly transparent substrate disposed on the first visibly transparent electrode, wherein the visibly transparent substrate comprises glass, a rigid polymer, or a flexible polymer.
25. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell has a power conversion efficiency greater than or equal to about 0.3%.
26. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell has an external quantum efficiency at any wavelength less than about 450 nm of greater than or equal to about 20%.
27. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell does not include an additional active layer having a bandgap of less than 2.75 eV.
28. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell does not include an additional active layer with an external quantum efficiency greater than about 10% at wavelengths greater than about 450 nm.
29. A transparent photovoltaic cell comprising: a substrate; a first electrode; an active layer comprising a light absorbing material that only absorbs ultraviolet (UV) light having a wavelength of less than about 450 nm, the light absorbing material being either: a halide perovskite, or a metal halide, a metal nitride, a metal sulfide, a metal selenide, a metal telluride, an alloy thereof, or a combination thereof; and a second electrode, wherein the first electrode is located between the substrate and the active layer and the active layer is located between the first electrode and the second electrode, and wherein each of the substrate, the first electrode, the active layer, and the second electrode are visibly transparent, such that the transparent photovoltaic cell has an average visible transparency of greater than or equal to about 50%.
30. (canceled)
31. The transparent photovoltaic cell according to claim 29, further comprising: a first visibly transparent adjunct layer located between the first electrode and the active layer; and a second visibly transparent adjunct layer located between the active layer and the second electrode, wherein the first visibly transparent adjunct layer is an electron transport layer, an electron extraction layer, a hole blocking layer, or a buffer layer, and the second visibly transparent adjunct layer is an electron transport layer or an electron extraction layer.
32. (canceled)
33. (canceled)
34. A transparent photovoltaic cell comprising: a first visibly transparent electrode; a second visibly transparent electrode; and a visibly transparent active layer disposed between the first visibly transparent electrode and the second visibly transparent electrode, the active layer comprising a light absorbing material that only absorbs light having a wavelength of less than about 450 nm and that is substantially nonabsorbent to light having a wavelength of greater than or equal to about 450 nm, wherein the light absorbing material is either: a halide perovskite having the formula ABX.sub.3, where A is methylammonium (MA), formamidinium (FA), ethanediammonium (EA), iso-propylammonium, dimethylammonium, guanidinium, piperidinium, pyridinium, pyrrolidinium, imidazolium, t-butylammonium, Na, K, Rb, Cs, or a combination thereof; B is Pb, Sn, Ge, Cu, Sr, Ti, Mn, Bi, Zn, or a combination thereof; and X is a halide or a combination of halides, or a metal halide comprising at least one of PbI.sub.2, PbCl.sub.2, PbBr.sub.2, PbI.sub.XBr.sub.(1-X), PbI.sub.XCl.sub.(1-X), PbBr.sub.XCl.sub.(1-X), Snl.sub.2, SnCl.sub.2, SnBr.sub.2, SnI.sub.XBr.sub.(1-X), SnBr.sub.XCl.sub.(1-X), Gel.sub.2, GeCl.sub.2, GeBr2, GeI.sub.XBr.sub.(1-X), GeI.sub.XCl.sub.(1-X), GeBr.sub.XCl.sub.(1-X), InI.sub.3, InCl.sub.3, InBr.sub.3, TiI.sub.3, TiCl.sub.3, TiBr.sub.3, GaI.sub.3, GaBr3, GaCl.sub.3, AlCl.sub.3, AlBr.sub.3, AlI.sub.3, A.sub.2TiI.sub.6, A.sub.2TiCl.sub.6, and A.sub.2TiBr.sub.6, where A is an alkali metal, an organic cation, or a combination thereof, a metal nitride comprising at least one of In.sub.(X)Ga.sub.(1-X)N and In.sub.(X)Al.sub.(1-X)N, a metal sulfide comprising ZnS.sub.(X)Se.sub.(1-X), a metal selenide comprising at least one of ZnSe, ZnO.sub.(X)Se.sub.(1-X), and Zn.sub.(X)Mg.sub.(1-X)Se, a metal telluride comprising at least one of Zn.sub.(X)Mg.sub.(1-X)Te and BeSe.sub.(X)Te.sub.(1-X), an alloy thereof, or a combination thereof, and wherein 0x1.
35. The transparent photovoltaic cell according to claim 34, wherein the transparent photovoltaic cell is a rigid display screen, a flexible display screen, a watch crystal, an automotive glass, a smart window, an autonomous electrochromic window, or an architectural glass.
36. The transparent photovoltaic cell according to claim 35, wherein the transparent photovoltaic cell is integrated into a multijunction photovoltaic cell.
37. The transparent photovoltaic cell according to claim 1, wherein the transparent photovoltaic cell is configured as a tandem structure wherein the transparent photovoltaic cell is joined to at least one subcell via a recombination zone.
Description
DRAWINGS
[0046] The drawings described herein are for illustrative purposes only of selected embodiments and not all possible implementations, and are not intended to limit the scope of the present disclosure.
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DETAILED DESCRIPTION
[0101] Example embodiments are provided so that this disclosure will be thorough, and will fully convey the scope to those who are skilled in the art. Numerous specific details are set forth such as examples of specific compositions, components, devices, and methods, to provide a thorough understanding of embodiments of the present disclosure. It will be apparent to those skilled in the art that specific details need not be employed, that example embodiments may be embodied in many different forms and that neither should be construed to limit the scope of the disclosure. In some example embodiments, well-known processes, well-known device structures, and well-known technologies are not described in detail.
[0102] The terminology used herein is for the purpose of describing particular example embodiments only and is not intended to be limiting. As used herein, the singular forms a, an, and the may be intended to include the plural forms as well, unless the context clearly indicates otherwise. The terms comprises, comprising, including, and having, are inclusive and therefore specify the presence of stated features, elements, compositions, steps, integers, operations, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof. Although the open-ended term comprising, is to be understood as a non-restrictive term used to describe and claim various embodiments set forth herein, in certain aspects, the term may alternatively be understood to instead be a more limiting and restrictive term, such as consisting of or consisting essentially of. Thus, for any given embodiment reciting compositions, materials, components, elements, features, integers, operations, and/or process steps, the present disclosure also specifically includes embodiments consisting of, or consisting essentially of, such recited compositions, materials, components, elements, features, integers, operations, and/or process steps. In the case of consisting of, the alternative embodiment excludes any additional compositions, materials, components, elements, features, integers, operations, and/or process steps, while in the case of consisting essentially of, any additional compositions, materials, components, elements, features, integers, operations, and/or process steps that materially affect the basic and novel characteristics are excluded from such an embodiment, but any compositions, materials, components, elements, features, integers, operations, and/or process steps that do not materially affect the basic and novel characteristics can be included in the embodiment.
[0103] Any method steps, processes, and operations described herein are not to be construed as necessarily requiring their performance in the particular order discussed or illustrated, unless specifically identified as an order of performance. It is also to be understood that additional or alternative steps may be employed, unless otherwise indicated.
[0104] When a component, element, or layer is referred to as being on, engaged to, connected to, or coupled to another element or layer, it may be directly on, engaged, connected or coupled to the other component, element, or layer, or intervening elements or layers may be present. In contrast, when an element is referred to as being directly on, directly engaged to, directly connected to, or directly coupled to another element or layer, there may be no intervening elements or layers present. Other words used to describe the relationship between elements should be interpreted in a like fashion (e.g., between versus directly between, adjacent versus directly adjacent, etc.). As used herein, the term and/or includes any and all combinations of one or more of the associated listed items.
[0105] Although the terms first, second, third, etc. may be used herein to describe various steps, elements, components, regions, layers and/or sections, these steps, elements, components, regions, layers and/or sections should not be limited by these terms, unless otherwise indicated. These terms may be only used to distinguish one step, element, component, region, layer or section from another step, element, component, region, layer or section. Terms such as first, second, and other numerical terms when used herein do not imply a sequence or order unless clearly indicated by the context. Thus, a first step, element, component, region, layer or section discussed below could be termed a second step, element, component, region, layer or section without departing from the teachings of the example embodiments.
[0106] Spatially or temporally relative terms, such as before, after, inner, outer, beneath, below, lower, above, upper, and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. Spatially or temporally relative terms may be intended to encompass different orientations of the device or system in use or operation in addition to the orientation depicted in the figures.
[0107] Throughout this disclosure, the numerical values represent approximate measures or limits to ranges to encompass minor deviations from the given values and embodiments having about the value mentioned as well as those having exactly the value mentioned. Other than in the working examples provided at the end of the detailed description, all numerical values of parameters (e.g., of quantities or conditions) in this specification, including the appended claims, are to be understood as being modified in all instances by the term about whether or not about actually appears before the numerical value. About indicates that the stated numerical value allows some slight imprecision (with some approach to exactness in the value; approximately or reasonably close to the value; nearly). If the imprecision provided by about is not otherwise understood in the art with this ordinary meaning, then about as used herein indicates at least variations that may arise from ordinary methods of measuring and using such parameters. For example, about may comprise a variation of less than or equal to 5%, optionally less than or equal to 4%, optionally less than or equal to 3%, optionally less than or equal to 2%, optionally less than or equal to 1%, optionally less than or equal to 0.5%, and in certain aspects, optionally less than or equal to 0.1%.
[0108] In addition, disclosure of ranges includes disclosure of all values and further divided ranges within the entire range, including endpoints and sub-ranges given for the ranges. As referred to herein, ranges are, unless specified otherwise, inclusive of endpoints and include disclosure of all distinct values and further divided ranges within the entire range. Thus, for example, a range of from A to B or from about A to about B is inclusive of A and B.
[0109] Example embodiments will now be described more fully with reference to the accompanying drawings.
[0110] The current technology provides transparent solar cell designs, e.g., transparent photovoltaic devices (TPV). The term transparent as used herein encompasses an average visible transparency of a straight through beam of greater than or equal to about 45%. The term semi-transparent as used herein encompasses an average visible transparency of a straight through beam of greater than or equal to about 10% to less than or equal to about 45%. In general, the designs include molecular active layers with strong absorption features outside of the visible light spectrum, e.g., in the ultraviolet (UV) solar spectrum. The devices may include selective high-reflectivity anti-reflection contact coatings. Devices may be formed as heterojunction solar cells with a second light absorbing layers having peak-absorption in the ultraviolet (UV) solar spectrum. Whereas the second light absorbing material absorbs UV light, it is substantially nonabsorbent (as defined below) to light having a wavelength of greater than or equal to about 450 nm, greater than or equal to about 475 nm, or greater than or equal to about 500 nm. Such devices may be formed in a tandem structure with one or more subcells joined via a recombination zone. Such devices may be used in a variety of applications including rigid and flexible computer display screens used in a desktop monitor, laptop or notebook computer, tablet computer, mobile phone, e-reader and the like. Other applications include watch crystals, automotive and architectural glass, including sunroofs, smart windows, autonomous electrochromic windows, and privacy glass. The photovoltaic devices may be used for active power generation, e.g., for completely self-powered applications, and battery charging (or battery life extension).
[0111] Near-infrared (NIR) as recited herein is defined as light having wavelengths in the range of greater about 650 to less than or equal to about 2000 nanometers (nm). Ultraviolet (UV) as recited herein is defined as light having wavelengths of greater than about 10 nm and less than about 450 nm. The use of an active layer having absorption in the UV allows for the use of selective high-reflectivity coatings to optimize device performance while also permitting high transmission of visible light through the entire device. Visible light as recited herein is defined as light having wavelengths to which the human eye has a significant response, from greater than or equal to about 450 nm to less than or equal to about 650 nm.
[0112] Halide perovskite materials have emerged as a Si replacement with excellent photovoltaic properties, certified efficiency up to 22.7%, and extremely low cost. There has been growing interest in applying halide perovskites to semitransparent and spatially segmented transparent photovoltaics (TPVs) to enable a greater range of deployment routes. However, the continuous band absorption of these semiconductors prevents near-infrared selective wavelength harvesting typically targeted for transparent photovoltaics (TPVs) with the highest efficiency and highest transparency needed to meet the aesthetic demands of many emerging applications. The current technology provides for the development of TPVs based on perovskite semiconductors where the bandgap is sensitively tuned with a key range of compositions to selectively harvest only ultraviolet (UV) photons with bandgaps between 400-440 nm. This range is important because bandgaps less than about 380 nm have much lower theoretical efficiency limits of less than 2.5% and bandgaps greater than about 450 nm will impart unacceptable levels of color tinting or poor color rendering index (CRI). TPV devices are demonstrated with power conversion efficiency (PCE) up to 0.52%, average visible transparency (AVT) up to 70.7%, and CRI over 92. This approach offers theoretical efficiencies up to 7% with 100% visible transparency and CRIs greater than about 90. Practical optimization of these perovskite cells, currently limited by quantum efficiencies of only 20-30%, could quickly yield TPVs with PCEs between 3-5%, rivaling state of the art near-infrared-harvesting TPVs, while also providing a route to higher efficiency multi-junction TPVs when coupled with near-infrared harvesting TPVs.
[0113] An exemplary transparent photovoltaic cell 10 according to various aspects of the current technology is shown in
[0114] As discussed further below, the transparent photovoltaic cell 10 can comprise more than one active layer 14 in various embodiments. Such active layers 14 have a bandgap of greater than or equal to about 2.75 eV or have an external quantum efficiency of less than 10% at wavelengths greater than about 450 nm. Put another way, the transparent photovoltaic cell 10 does not include an additional active layer having a bandgap of less than 2.75. Alternatively, the transparent photovoltaic cell 10 does not include an additional active layer that generates an external quantum efficiency greater than about 10% at wavelengths greater than about 450 nm.
[0115] In various embodiments, the light absorbing material has a bandgap greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV. For example, in various embodiments the light absorbing material has a bandgap of about 2.75 eV, about 2.8 eV, about 2.85 eV, about 2.9 eV, about 2.95 eV, about 3 eV, about 3.05 eV, about 3.1 eV, about 3.15 eV, or about 3.2 eV. Accordingly, the light absorbing material absorbs UV light having a wavelength of less than or equal to about 470 nm, less than or equal to about 460 nm, less than or equal to about 450 nm, less than or equal to about 440 nm, less than or equal to about 430 nm, less than or equal to about 420 nm, less than or equal to about 410 nm, or less than or equal to about 400 nm.
[0116] Whereas the light absorbing material absorbs UV light, it is substantially nonabsorbent to light having a wavelength of greater than or equal to about 450 nm, greater than or equal to about 460 nm, or greater than or equal to about 470 nm. By substantially nonabsorbent it is meant that the light absorbing material absorbs less than or equal to about 25%, less than or equal to about 20%, less than or equal to about 15%, less than or equal to about 10%, less than or equal to about 5%, or less than or equal to about 1% of the light having a wavelength greater than or equal to about 450 nm, greater than or equal to about 460 nm, or greater than or equal to about 470 nm. For example, in some embodiments the light absorbing material may have a peak absorption at a wavelength of less than about 450 nm, but which tails off into the visible region at a wavelength of greater than about 450 nm and beyond. In such an embodiment, it is understood that the light absorbing material absorbs some visible light that is associated with the tail. Further, transparent photovoltaic cell 10, as fully assembled, has a largest peak absorption in the active layer at a wavelength less than or equal to about 450 nm.
[0117] The transparent photovoltaic cell 10 is transparent. As such, the transparent photovoltaic cell 10 transmits visible light and has an average visible transparency (AVT) of greater than or equal to about 45%, greater than or equal to about 50%, greater than or equal to about 55%, greater than or equal to about 60%, greater than or equal to about 65%, greater than or equal to about 70%, greater than or equal to about 75%, greater than or equal to about 80%, greater than or equal to about 85%, or greater than or equal to about 90%. Further, the transparent photovoltaic cell 10 has a CRI of greater than or equal to about 80, greater than or equal to about 85, greater than or equal to about 90, or greater than or equal to about 95, referenced to an air mass 1.5 global (AM 1.5 G) solar spectrum. Therefore, in various embodiments, the transparent photovoltaic cell 10 is visibly transparent, such that when a human observer looks through the transparent photovoltaic cell 10, objects on an opposing side of the transparent photovoltaic cell 10 than the human observer appear substantially (or completely) in their natural color and substantially without (or without) tint or haze.
[0118] The transparent photovoltaic cell 10 also provides heat savings by reflecting NIR and IR light. More particularly, the transparent photovoltaic cell 10 has a strongest peak reflectance of greater than or equal to about 10%, greater than or equal to about 15%, greater than or equal to about 20%, greater than or equal to about 25%, greater than or equal to about 35%, greater than or equal to about 40%, or greater than or equal to about 50% at wavelengths of greater than or equal to about 650 nm to less than or equal to about 5000 nm. Although the light absorbing material is substantially or completely nonabsorbent to light having wavelengths of greater than or equal to about 650 nm to less than or equal to about 5000 nm, other components of the transparent photovoltaic cell 10, such as, for example, the electrodes, may absorb a portion of the light having wavelengths (in addition to reflection) of greater than or equal to about 650 nm to less than or equal to about 5000 nm that is not reflected. Another portion of the light having wavelengths of greater than or equal to about 650 nm to less than or equal to about 5000 nm that is not reflected is transmitted through the transparent photovoltaic cell 10. Accordingly, the transparent photovoltaic cell 10 can replace a low-e window or can be combined with a low-e coating or window. In another embodiment, the transparent photovoltaic cell 10 is integrated into a multijunction photovoltaic cell or device.
[0119] The transparent photovoltaic cell 10 has a power conversion efficiency (PCE) of greater than or equal to about 0.3%, greater than or equal to about 0.5%, greater than or equal to about 1%, greater than or equal to about 1.5%, greater than or equal to about 3%, greater than or equal to about 5%, greater than or equal to about 6%, or greater than or equal to about 7%.
[0120] The transparent photovoltaic cell 10 has an external quantum efficiency (EQE) at any wavelength less than about 450 nm of greater than or equal to about 20%, greater than or equal to about 30%, greater than or equal to about 40%, greater than or equal to about 50%, greater than or equal to about 60%, greater than or equal to about 70%, or greater than or equal to about 80%.
[0121] The light absorbing material of the active layer 14 is either a halide perovskite or a metal halide, a metal nitride, a metal sulfide, a metal selenide, a metal telluride, an alloy thereof, or a combination thereof. The light absorbing material is provided as a thin layer, nanoparticles, or nanocrystals.
[0122] In various embodiments, the light absorbing material of the active layer 14 is a halide perovskite. A perovskite is a material that has the same type of crystal structure as calcium titanium oxide (CaTiO.sub.3; i.e., naturally occurring perovskite). The crystal structure is known as the perovskite structure or .sup.XIIA.sup.2+VIB.sup.4+X.sup.2.sub.3 with oxygen in the face centers. The general formula for a perovskite compound is ABX.sub.3, where the A and B cations are cations of different sizes (the A cation typically being a 1.sup.+ cation that is larger than the B cation, which is typically a 2.sup.+ cation) and X is an anion that bonds to both A and B. The ideal cubic-symmetry structure has the B cation in 6-fold coordination, surrounded by an octahedron of anions, and the A cation in 12-fold octahedral coordination. In various embodiments, the light absorbing material includes at least one perovskite, hybrid halide perovskite, oxide perovskite, layered halide perovskite, or at least one inorganic halide perovskite. Hybrid halide perovskites have the formula ABX.sub.3, where A is methylammonium (MA), formamidinium (FA), ethanediammonium (EA), iso-propylammonium, dimethylammonium, guanidinium, piperidinium, pyridinium, pyrrolidinium, imidazolium, t-butylammonium, Na, K, Rb, Cs, or a combination thereof; B is Pb, Sn, Ge, Cu, Sr, Ti, Mn, Bi, Zn, or a combination thereof; and X is a halide or a combination of halides. By blending various A, B, and X components, the halide perovskite can be tuned to have a desired bandgap. For example, the bandgap generally increases as the halide X is changed from I to Br to Cl to F.
[0123] In some embodiments, the halide perovskite comprises F, Cl, Br, and I and has a bandgap of greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV.
[0124] In some embodiments, the halide perovskite comprises F and at least one other halide.
[0125] In some embodiments, the halide perovskite comprises Cl and at least one other halide.
[0126] In some embodiments, the halide perovskite comprises Br and at least one other halide.
[0127] In some embodiments, the halide perovskite comprises I and at least one other halide.
[0128] In various embodiments, the light absorbing material of the active layer 14 is a metal halide, a metal nitride, a metal sulfide, a metal selenide, a metal telluride, alloys thereof, and combinations thereof. The metal halide comprises at least one of PbI.sub.2, PbCl.sub.2, PbBr.sub.2, PbI.sub.XBr.sub.(1-X), PbI.sub.XCl.sub.(1-X), PbBr.sub.XCl.sub.(1-X), SnI.sub.2, SnCl.sub.2, SnBr.sub.2, SnI.sub.XBr.sub.(1-X), SnI.sub.XCl.sub.(1-X), SnBr.sub.XCl.sub.(1-X), GeI.sub.2, GeCl.sub.2, GeBr.sub.2, GeI.sub.XBr.sub.(1-X), GeI.sub.XCl.sub.(1-X), GeBr.sub.XCl.sub.(1-X), InI.sub.3, InCl.sub.3, InBr.sub.3, TiI.sub.3, TiCl.sub.3, TiBr.sub.3, GaI.sub.3, GaBr.sub.3, GaCl.sub.3, AlCl.sub.3, AlBr.sub.3, AlI.sub.3, A.sub.2TiI.sub.6, A.sub.2TiCl.sub.6, and A.sub.2TiBr.sub.6, where A is an alkali metal (Li, Na, K, Rb, Cs, or a combination thereof), an organic cation (methylammonium (MA), formamidinium (FA), ethanediammonium (EA), iso-propylammonium, dimethylammonium, guanidinium, piperidinium, pyridinium, pyrrolidinium, imidazolium, t-butylammonium or a combination thereof), or a combination thereof; the metal nitride comprise at least one of In.sub.(X)Ga.sub.(1-X)N and In.sub.(X)Al.sub.(1-X)N; the metal sulfide comprises ZnS.sub.(X)Se.sub.(1-X); the metal selenide comprises at least one of ZnSe, ZnO.sub.(X)Se.sub.(1-X) and Zn.sub.(X)Mg.sub.(1-X)Se; and the metal telluride comprises at least one of Zn.sub.(X)Mg.sub.(1-X)Te and BeSe.sub.(X)Te.sub.(1-X), wherein for all of the above formulas 0x1. In some embodiments, the light absorbing material is at least one of In.sub.(X)Ga.sub.(1-X)N (0.05x0.25), In.sub.(X)Al.sub.(1-X)N (0.25x0.7), ZnS.sub.(X)Se.sub.(1-X) (0.1x0.9), Zn.sub.(X)Mg.sub.(1-X)SE (0.05x0.5), Zn.sub.(X)Mg.sub.(1-X)Te (0.05x0.95), and BeSe.sub.(X)Te.sub.(1-X) (0.6x1). By at least one of selecting suitable values for x and blending various light absorbing materials together, the light absorbing material can be tuned to have a desired bandgap, i.e., a bandgap of greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV, as discussed above. For example, x can be chosen to provide a light absorbing material with a bandgap of greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV, a plurality (at least two) of light absorbing materials can be combined to provide a bandgap of greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV, or both.
[0129] It is understood that while the light absorbing material is either a halide perovskite or a metal halide, a metal nitride, a metal sulfide, a metal selenide, a metal telluride, alloys thereof, and combinations thereof, these materials are limited in that they must be assembled into the transparent photovoltaic cell 10 and comply with each of the requirements set forth above, including the bandgap requirements, the absorption requirements, the transmittance requirements, the CRI requirements, the PCE requirements, and the EQE requirements.
[0130] The active layer 14 has a thickness T.sub.AL of greater than or equal to about 5 nm to less than or equal to about 5000 nm, greater than or equal to about 10 nm to less than or equal to about 1000 nm, greater than or equal to about 50 nm to less than or equal to about 600 nm, greater than or equal to about 100 nm to less than or equal to about 500 nm, or greater than or equal to about 200 nm to less than or equal to about 400 nm.
[0131] The first electrode 12 and the second electrode 16 are independently a visibly transparent anode and a visibly transparent cathode. The first and second electrodes 12, 16 comprise a visibly transparent electrically conducting material individually selected from the group consisting of a conducting oxide, such as indium tin oxide (ITO), aluminum doped zinc oxide (AZO), fluorine doped tin oxide (FTO), indium zinc oxide, InZnAlO (IZAO, e.g., 90 wt. % In.sub.2O.sub.3, 5 wt. % ZnO, and 5 wt. % Al.sub.2O.sub.3), InAlZnSnO (IZATO), zinc oxide, ZnAlO (ZAO), cadmium oxide, zirconium indium oxide (ZrIO), and gallium zinc oxide (GZO), a metal, such as Al, Au, Ag, Mo, Cu, or Ni, carbon, graphene, graphene oxide, poly(3, 4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), and combinations thereof. The visibly transparent electrically conducting material can be a thin film, an ultrathin film, nanowires (e.g., of Al, Au, Ag, Mo, Cu, and/or Ni), a nanowire mesh, nanotubes (e.g., carbon nanotubes, nanoparticles, or a combination thereof.
[0132] In some embodiments, at least one of the first electrode 12 and the second electrode 16 comprises a first layer comprising the visibly transparent electrically conducting material and a second layer comprising a transparent electrically conducting organic material. In
[0133] The first electrode 12 has a thickness T.sub.E1 and the second electrode 16 has a thickness T.sub.E2, wherein thickness T.sub.E1 and thickness T.sub.E2 are individually and independently greater than or equal to about 1 nm to less than or equal to about 200 nm, greater than or equal to about 50 nm to less than or equal to about 150 nm, or greater than or equal to about 75 nm to less than or equal to about 125 nm.
[0134] In some embodiments, one of the first electrode 12 or the second electrode 16 is disposed on a substrate. For example,
[0135]
[0136] In various embodiments, the third transparent photovoltaic cell 10 comprises the optional first adjunct layer 22 as a hole transport layer/work function modifying layer/buffer layer/hole selective layer, wherein work function modifying layers are added to get a wetting. Here, the optional first adjunct layer 22 comprises poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), poly(3-hexylthiophene-2,5-diyl) (P3HT), N,N-Bis(naphthalen-1-yl)-N,N-bis(phenyl)-2,2-dimethylbenzidine (NPD), N,N-Bis(3-methylphenyl)-N,N-bis(phenyl)-benzidine (TPD), 2,2,7,7-Tetrakis(N,N-diphenylamino)-2,7-diamino-9,9-spirobifluorene (spiro-TAD), Poly[N,N-bis(4-butylphenyl)-N,N-bis(phenyl)-benzidine](poly-TPD), CuSCN, CuI, MoO.sub.3, NiO, or a combination thereof.
[0137] In various embodiments, the third transparent photovoltaic cell 10 comprises the optional second adjunct layer 24 as an electron transport layer/electron extraction layer. Here, the optional second adjunct layer 24 comprises a fullerene, such as C.sub.60, C.sub.70, C.sub.84, or phenyl-C.sub.61-butyric-acid-methyl-ester (PCBM), ZnO, TiO.sub.2, NiO, MoO.sub.3, nanotubes, conductive nanoparticles (e.g., ITO), or a combination thereof. For example, the role of fullerenes in perovskite solar cells is typically to aid in electron extraction, and therefore, layers should be as thin as possible to prevent tail state absorption: less than or equal to about 40 nm, less than or equal to about 20 nm, less than or equal to about 10 nm, less than or equal to about 5 nm, or less than or equal to about 1 nm.
[0138] In various embodiments, the third transparent photovoltaic cell 10 comprises the optional third adjunct layer 26 as an electron transport layer/electron extraction layer/buffer layer/hole blocking layer. The optional third adjunct layer 26 provides an ohmic contact between the active layer 14 and the second electrode 16. Here, the optional third adjunct layer 26 comprises [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), Al-doped ZnO (AZO), TiO.sub.2, bathocuproine (BCP), MoO.sub.3, or a combination thereof.
[0139] The optional first adjunct layer 22 has a thickness T.sub.AL1, the optional second adjunct layer 24 has a thickness T.sub.AL2, and the optional third adjunct layer 26 has a thickness T.sub.AL3. T.sub.AL1, T.sub.AL2, and T.sub.AL3 are independently and individually greater than or equal to about 0.05 nm to less than or equal to about 100 nm. When the optional second adjunct layer 24 comprises a fullerene, the thickness T.sub.AL2 is less than or equal to about 50 nm.
[0140] When the third transparent photovoltaic cell 10 comprises an adjunct layer 22, 24, 26 that is an electron transport layer or a hole transport layer, the electrode 12, 16 that is located adjacent to the electron transport layer is the cathode and the electrode 12, 16 that is adjacent to the hole transport layer is the anode.
[0141]
[0142] Any of the transparent photovoltaic cells described herein can be used as a rigid display screen, a flexible display screen, a watch crystal, an automotive glass, or an architectural glass, as non-limiting examples.
[0143] The current technology also provides a method of fabricating a transparent photovoltaic cell. The method comprises tuning a light absorbing material to have an acceptable bandgap as described above. When the light absorbing material is a halide perovskite, tuning is performed by blending various A, B, and X components. When the light absorbing material is a metal halide, a metal nitride, a metal sulfide, a metal selenide, a metal telluride, an alloy thereof, or a combination thereof, tuning is performed by alloying or blending various metal halides, metal nitrides, metal sulfides, metal selenides, metal tellurides, or alloys thereof together to provide a bandgap greater than or equal to about 2.75 eV and less than or equal to about 3.2 eV.
[0144] The method comprises sequentially disposing the following layers onto a visibly transparent substrate: a layer comprising a first electrode, a layer comprising a light absorbing material, and a layer comprising a second electrode. In various embodiments, the method also includes disposing adjunct layers throughout the transparent photovoltaic cell.
[0145] The disposing of the various layers can be performed by any means known in the art. Non-limiting examples of means for disposing the various layers include spin coating, dip coating, doctor blading, chemical vapor deposition (CVD), drop casting, spray coating, plasma-sputtering, vacuum depositing, and combinations thereof. Moreover, the layer comprising a perovskite material may be deposited additive-free in a one-step synthesis or additive-free in a two or more step synthesis. In a one-step synthesis, all perovskite reactants (e.g., PbI.sub.2 and MAI) are deposited from one solution. A two or more-step synthesis involves the deposition of one of the reactants followed by reaction with a second reactant, either as a second deposited layer or as a gas phase diffusion process, for example.
[0146] As described above in regard to the devices, the adjunct layers, which can be, for example, hole transport layers or electron transport layers, may include a single layer or a plurality of layers. The layer or layers are deposited individually and sequentially.
[0147] When all the layers have been deposited, the method comprises annealing the device at a temperature of from about 75 C. to about 150 C., such as a temperature of about 90 C., from about 2 minutes to about 60 minutes or longer. In some embodiments, annealing is conducted for about 10 minutes.
[0148] Embodiments of the present technology are further illustrated through the following non-liming examples.
EXAMPLE 1
[0149] Halide perovskite tunability is used as a platform for creating UV harvesting TPVs with near ideal bandgaps and visible absorption cutoffs that enable high AVT and CRI. TPV devices from various halide perovskite compositions are demonstrated with a PCE of up to 0.52% simultaneously with an AVT of 70% and a CRI over 92. Given that these cells are limited by quantum efficiencies of 20-30%, efficiencies above 3% are achievable because halide perovskites cells now readily achieve quantum efficiencies above 90%. New halide perovskite compositions for application in highly transparent photovoltaics and TPV multi-junctions are demonstrated.
Methods
[0150] Materials and Precursor Preparation: Dimethylformamide (DMF, 99.8%, Aldrich.), dimethyl sulfoxide (DMSO, 99.9%, Aldrich.), PEDOT:PSS (Clevios PVP Al 4083, Heraeus; diluted to 10% by water for use), CH.sub.3NH.sub.3Cl (MACl, 98%, Aldrich.), PbBr.sub.2 (99%, Aldrich.), PbCl.sub.2 (98%, Aldrich.), C.sub.60 (99.9%, MER.), 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (BCP, 99%, Lumtech.) and Tris-(8-hydroxy-quinolinato)aluminium (Alq.sub.3, 99.5%, Lumtech.) are used as received. To prepare the mixed halide perovskite precursor solution, MACl:PbBr.sub.2:PbCl.sub.2 (135 mg, 220 mg and 389 mg, respectively) is added in a mixed solvent of DMF and DMSO (1.5 ml and 0.5 ml, respectively). For pure chloride perovskite precursor solution, MACl: PbCl.sub.2 (67.5 mg and 278 mg, respectively) is added in a mixed solvent of DMF and DMSO (1.5 ml and 0.5 ml, respectively). The solutions are then stirred for 30 minutes and filtered with 0.45 m PTFE filters before use.
[0151] Device Fabrication: The PEDOT solution is spin-coated onto pre-cleaned ITO substrates at 6000 rpm for 10 seconds and then annealed at 100 C. for 5 minutes. The perovskite precursor is spin-coated on top of the PEDOT film at 5000 rpm for 12 seconds, and then moved into a homemade vacuum chamber, evacuated to approximately 10 mTorr, and left in the chamber for 1 minute. The samples are then treated by methylamine gas for 2 seconds. The substrate is then moved into the evaporation chamber for deposition of C.sub.60 (20 nm) as an electron extraction layer and BCP (7.5 nm) for ohmic contact. Finally, 5 nm thick of silver layer and 60 nm of Alq.sub.3 are deposited as the transparent electrode by thermal evaporation through a shadow mask with a final measured device area of 4.85 mm.sup.2.
[0152] Measurement and Characterization: UV-VIS-NIR transmission and reflection spectra are collected using PerkinElmer Lambda 800 spectrometer. XRD data is measured using CuK (0.154 nm) emission with a Bruker D2 phaser. A field-emission scanning electron microscopy (Carl Zeiss Auriga Dual Column FIB SEM) is used to acquire SEM images. The current density-voltage characteristics (J-V curves) are obtained using a Keithley 2420 sourcemeter under both dark and AM1.5 G solar simulation, where the light intensity is measured using a NREL-calibrated Si reference cell with KG5 filter (xenon arc lamp with the spectral-mismatch factor of 1.20). Devices are scanned at a rate of 50 mV s.sup.1. The spectral mismatch for UV-only TPVs is considerably more sensitive to lamp spectra measurements due to a large difference in a quantum efficiency of the tested cell versus a calibrated Si reference cell. EQE measurements are performed using a QTH lamp with a monochromator, chopper, lock-in amplifier, and calibrated Si detector to measure the intensity. The J-V and EQE are measured on un-encapsulated devices/samples in ambient air. The IQE is evaluated by measuring the device absorption via reflectivity measurements of the overall device (A=1RT).
Results
[0153] Methylammonium (MA) lead halide is a perovskite semiconductor. While other compositions are being actively investigated, little work has been done to optimize devices with bandgaps near the visible absorption edge.
[0154] UV-harvesting perovskite films are prepared by solution deposition via spin-coating. Due to the limited solubility of many Cl precursors in typical solvents, greater attention to the processing is required to form smooth perovskite layers with minimal haze and roughness to prevent shorting. A vacuum-assisted solution deposition process is combined with methylamine gas post-treatment to obtain high quality films that are highly transparent with minimal light scattering. Scanning electron microscopy (SEM) images of MAPbCl.sub.3 and MAPbCl.sub.2.4Br.sub.0.6 films provided in
[0155] Photographs of various halide perovskite films are shown in
[0156] UV harvesting TPVs are prepared with the architecture shown in
Discussion
[0157] Subsequently, the optical properties of UV harvesting TPV devices are systematically investigated. Provided in
TABLE-US-00001 TABLE 1 Summary of device parameters for UV-only harvesting TPV devices. The bandgap was measured from optical absorption of halide perovskite films as shown in FIG. 10. V.sub.OC J.sub.SC FF PCE Bandgap AVT Device (V) (mA cm.sup.2) (%) (%) (eV) (%) CRI MAPbCl.sub.3 1.11 0.11 0.61 0.9 35.8 3.7 0.24 0.04 3.04 70.7 92.4 (best) (1.18) (0.67) (41.1) (0.33) MAPbCl.sub.2.4Br.sub.0.6 1.13 0.09 0.85 0.9 43.5 3.1 0.42 0.06 2.83 69.7 93.1 (best) (1.26) (0.92) (44.9) (0.52)
[0158] Despite demonstrating UV harvesting TPV devices from halide perovskite semiconductors with nearly ideal optical properties (absorption cutoffs, color rendering, and transparencies) these devices may still be limited by modest quantum efficiencies. Without being bound by theory, this likely stems from the poor solubility of chloride perovskite materials (limited to 30 wt. % in DMF and DMSO), which leads to thin perovskite films (100-150 nm) that can only harvest up to 60-70% of the UV light as shown in
TABLE-US-00002 TABLE 2 Theoretical efficiency limits of UV-only harvesting TPV devices. Absorption Cutoff V.sub.OC J.sub.SC PCE (nm) (V) (mA cm.sup.2) (%) 400 2.69 1.44 3.66 430 2.49 2.56 6.43 440 2.43 3.13 7.18
[0159] UV harvesting TPV devices have been demonstrated based on the platform of halide perovskite light absorbers. This indicates that the TPV devices selectively harvest UV light with ideal absorption cutoffs to minimize visual impact, while providing a pathway to maximizing performance. Based on mixed composition halide perovskites, TPV devices are shown with ideally tuned bandgap that exhibit up to 0.52% PCE with AVT of 70% and a CRI over 92. The high AVT of 70.7% makes these UV-harvesting TPV devices one of the highest performing highest-AVT photovoltaic cells reported to date. The foregoing reveals that the exceptional potential of perovskite materials effectively translates to TPV devices. These types of technologies are an important compliment to other near-infrared harvesting TPVs in rapidly reaching both single-junction and multi-junction efficiency limits.
EXAMPLE 2
[0160] TPV devices have a number of unique advantages compared with opaque photovoltaic devices. However, balancing efficiency and transparency has been difficult. Few TPV devices with PCE over 1% have been demonstrated when the AVT is over 70%. Here, a series of metal halide based TPVs with both increased efficiency and transparency are reported. The effect of metal halide layer thicknesses and compositions is systematically studied and subsequently, metal halide TPVs are evaluated with regard to efficiency, transparency, and stability. The results show that metal halide TPVs with UV wavelength selective absorption can achieve efficiencies exceeding 1% while the AVT is above 70%. Provided is a simple approach to prepare UV harvesting TPVs with high efficiency and high transparency that are viable as single junction cells or as a component to multi-junction transparent and opaque cells.
Background
[0161] Wavelength selective TPVs focus on converting invisible light to electric power, while allowing the majority of visible light (VIS) to pass through. This functionality provides great potential for deployment in non-traditional applications. There are two primary parameters of interest to TPVspower conversion efficiency (PCE) and average visible transmission (AVT). AVT is just as important as PCE, as it often defines the minimum threshold for deploying TPVs in new applications. In addition, color rendering index (CRI) is an important parameter for the adoptability of TPVs. Although the PCE of TPVs has been significantly improved to over 5% (with AVTs of about 50%), much work has focused on semitransparent PVs, even though many of the emerging applications are only enabled at the highest AVTs of about 70%.
[0162] Decreasing the absorption of visible light is key to improving the AVT and CRI of TPVs. A few reports have looked to selectively utilize ultraviolet (UV) light or near infrared (NIR) light absorption materials to produce the highest transparency devices. Further studies have reported a UV harvesting organic TPV achieving an AVT of 60% with a PCE of 1.5%, a series of organic salts with NIR harvesting properties and efficiency up to 0.9% with AVT of 60.4%, and organic-based NIR absorbing TPVs with PCEs between 0.9%-2.2% and AVT values (450-670 nm) of 62%-66%. In previous work, a UV wavelength-selective photovoltaic device with the AVT up to 73% was developed by exploiting the sharp wavelength cutoff enabled by tuning a perovskite bandgap right around the UV-visible cutoff. However, these previous efforts on developing highly transparent TPVs have shown that it is difficult to improve the TPV efficiency over 1% while the AVT simultaneously exceeds 70%, even though the theoretical limits for UV and UV/NIR harvesting TPVs are above 7% and 21%, respectively.
[0163] There are several types of metal halide semiconductors that exist, including bulk semiconductors and metal halide nanoclusters. The latter have been introduced in luminescent solar concentrators (LSC) and light-emitting diodes (LEDs) as a phosphorescent material, while the former have emerged as a byproduct from research on metal halide perovskite solar cells. Several metal halide semiconductors have been used as the light absorber in opaque solar cells, indicating the potential of metal halide materials in photovoltaic applications. For example, an InI-based solar cell (bandgap of 2.0 eV) has been reported. Although the device efficiency is only 0.4%, this demonstrates that InI is a viable photovoltaic material. Bismuth iodide (bandgap of 1.72 eV) has also been used in solar cells as the light harvest material and the efficiency of the photovoltaic devices has been shown up to 1.2%. However, since the bandgaps are in the visible range, these two metal halide materials are less suitable as a wavelength selective light absorber in TPVs. Stemming from research on lead halide perovskite solar cells, PbI.sub.2 (one of the perovskite precursors) has been found to work as a photovoltaic material. While the bandgap of PbI.sub.2 (2.4 eV) makes it less suitable for single-junction opaque cells as shown in
[0164] Here, metal halide based TPVs with an efficiency over 1% are demonstrated. The thickness and processing of the PbI.sub.2 active layer is first optimized and chloride and bromide doping is systematically investigated to understand the ability to modulate the bandgap. It is demonstrated that such an approach will work with bulk metal halides (non-perovskite structures) and the impact on physical and optoelectronic properties is shown. While the optical properties vary smoothly with doping, there is a sharp drop in electronic properties with Br and Cl doping past 10%. Based on this optimization, the resulting metal halide TPVs show device PCEs up to 1.22% with an AVT of 70.7%. Initial device stability is studied to further understand the impact of compositional doping, where bromine doping is found to increase lifetime. This demonstrates that simple metal halide semiconductors are useful as light harvesting materials for TPVs with high efficiency at the highest transparencies and that bandgaps can be modulated to achieve ideal cutoffs. The low cost and simple processing technique of metal halides provides a potential approach for TPVs in a variety of applications.
Methods
[0165] Materials and Precursor Preparation: Dimethylformamide (DMF, anhydrous, 99.8%, Aldrich.), PbI.sub.2 (99%, Aldrich.), PbBr.sub.2 (99%, Aldrich.), PbCl.sub.2 (98%, Aldrich), C.sub.60 (99.9%, MER Corporation.), 2,9-dimethyl-4,7-diphenyl-1,10-phenanthroline (BCP, Lumtech.), and tris-(8-hydroxy-quinolinato)aluminium (Alq.sub.3, 99.5%, Lumtech.) are used as received. Poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT, Clevios PVP Al 4083, 1.3 wt. %, Heraeus) is diluted to 10 vol. % with deionized water before use. To prepare the 1.0 M-PbI.sub.2 precursor solution, 461 mg PbI.sub.2 is added in 1.0 ml DMF. The solutions are then stirred for 1 hour and filtered with 0.45 m PTFE filters. The various concentrations of PbI.sub.2 solutions are prepared by diluting the 1 M-PbI.sub.2 solutions with DMF.
[0166] Device Fabrication: PEDOT solutions are spin-coated onto pre-cleaned ITO substrates at 6000 rpm for 10 seconds and then annealed at 110 C. for 2 minutes. The lead halide precursor solution is spin-coated on top of PEDOT film at 6000 rpm for 7 seconds, and then moved quickly into a homemade vacuum chamber, evacuated to the mTorr range, and left in the chamber for 3 minutes. The substrates are then transferred to the hot plate and annealed at 80 C. for 2 minutes. The substrates are then moved into the evaporation chamber for deposition of C.sub.60 (20 nm) and BCP (7.5 nm). Finally, a 5 nm thick silver electrode and 60 nm of Alq.sub.3 is deposited by thermal evaporation at a base pressure of 310.sup.6 Torr through a shadow mask with a final measured device area of 4.85 mm.sup.2. For the opaque device, a thermally 80 nm silver layer is deposited on the BCP layer as the electrode.
[0167] Measurement and Characterization: The thickness of the PbI.sub.2 film is measured by spectroscopic ellipsometry (Wollam Vase). UV-VIS-NIR transmission and reflection spectra are collected using a dual beam PerkinElmer Lambda 800 spectrometer. No reference sample is utilized for the transmission measurement. The current density-voltage characteristics (J-V curves) are obtained using a Keithley 2420 source measurement unit under both dark and AM1.5 G solar simulation, where the light intensity is measured using a NREL-calibrated Si reference cell with KG5 filter (xenon arc lamp with the spectral-mismatch factor of 1.080.02 for the devices studied). Devices are scanned at a rate of 50 mV/s. EQE measurements are performed using a QTH lamp with a calibrated Si detector, monochromator, chopper, and lock-in amplifier. The IQE is estimated as IQE=EQE/(1RT). The J-V and EQE are measured on un-encapsulated devices/samples in ambient air.
Results
[0168] PbI.sub.2 is a precursor material for lead halide perovskite films that has a hexagonal crystal structure.
[0169] Device parameters of opaque cells are summarized in
[0170] It is further demonstrated that the absorption range of lead halide materials unexpectedly can be readily modified by doping with various halide elements, analogous to perovskite films, despite the vastly different crystal structure (hexagonal versus perovskite). This is advantageous because it enables precise bandgap modification around the UV/VIS cutoff that is shown to be critical for the optimization of both PCE and AVT.
[0171] Lead halide TPVs are prepared with bromide or chloride doped PbI.sub.2 precursor solutions (10%) with the various solution concentrations of 0.1 M, 0.2 M and 0.3 M. Photographs of the fully assembled (unpatterned) TPV devices are shown in
TABLE-US-00003 TABLE 3 Summary of photovoltaic and transparency parameters for lead halide TPVs. [Pb] J.sub.SC V.sub.CC FF PCE AVT Device (mol L.sup.1) [mA cm.sup.2] [V] [%] [%] [%] CRI PbI.sub.2 0.1 1.94 0.14 0.998 0.03 51.9 1.7 1.00 0.06 65.9 87.5 0.2 2.02 0.08 1.07 0.02 55.0 1.0 1.19 0.06 69.2 89.3 0.3 1.88 0.05 1.02 0.04 53.2 2.3 1.02 0.06 70.7 91.3 PbI.sub.1.8Br.sub.0.2 0.1 2.01 0.06 1.02 0.02 55.9 1.6 1.15 0.07 65.8 88.8 0.2 2.00 0.05 1.05 0.02 55.1 1.5 1.16 0.05 69.1 90.2 0.3 1.82 0.04 0.966 0.01 51.0 3.6 0.929 0.08 68.8 91.4 PbI.sub.1.8Cl.sub.0.2 0.1 1.92 0.09 1.03 0.01 54.7 0.9 1.09 0.06 64.0 88.7 0.2 1.85 0.09 1.07 0.02 54.6 1.5 1.08 0.08 68.8 90.6 0.3 1.72 0.02 0.889 0.04 55.2 1.8 0.846 0.03 70.5 92.1
[0172] To investigate the optical properties, the reflection spectra of lead halide TPVs are further measured. The PbI.sub.1.8Br.sub.0.2 TPV device is used as a representative device for the optical properties of doped lead halide TPVs.
[0173] The EQE of the PbI.sub.1.8Br.sub.0.2 TPV device is also shown in
[0174] The photovoltaic performance of lead halide TPVs as a function of doping and thickness (concentration) is also systematically studied. The photovoltaic parameters of TPVs are summarized in Table 3 and plotted in
[0175] The initial stability of un-encapsulated TPVs is also evaluated (see
[0176] In summary, a series of lead halide TPV devices with both high efficiency and transparency is demonstrated. The thickness of the lead halide layer is systematically optimized. The bandgap and absorption of lead halide films are also finely tuned by doping the chloride and bromide into the pure PbI.sub.2. While the doping range is limited by sharp device performance reductions beyond 10% for Cl doping and 30% for Br doping, this demonstrates that bandgap tunability is achievable in these materials. Following comprehensive optimization, the lead halide TPVs are shown to achieve a PCE over 1.0%, while the AVT exceeds 70% and the CRI exceeds 90. This is one of the highest device efficiencies reported at the highest transparency and provides a path to higher performance TPVs and multi-junction TPVs using additional metal halides.
[0177] The foregoing description of the embodiments has been provided for purposes of illustration and description. It is not intended to be exhaustive or to limit the disclosure. Individual elements or features of a particular embodiment are generally not limited to that particular embodiment, but, where applicable, are interchangeable and can be used in a selected embodiment, even if not specifically shown or described. The same may also be varied in many ways. Such variations are not to be regarded as a departure from the disclosure, and all such modifications are intended to be included within the scope of the disclosure.