Monolithic solar cell

Abstract

A monolithic solar cell includes a first solar cell that is a sequential stack of an electrode, a silicon substrate, and an n-type emitter layer; a recombination layer disposed on the n-type emitter layer; an interfacial layer that is a double layer constituted of PEDOT:PSS and poly-TPD or PEDOT:PSS and PCDTBT, and that is disposed on the recombination layer; and a second solar cell that includes a p-type hole selective layer and a perovskite layer disposed on the p-type hole selective layer, the a p-type hole selective layer contacting and being integrated onto the interfacial layer of the first solar cell in a heat treatment during which the interfacial layer is partially decomposed, wherein the presence of the interfacial layer prevents a reduction in photoelectric conversion efficiency that occurs if the first solar cell and the second solar cell are combined without the presence of the interfacial layer.

Claims

1. A monolithic solar cell, comprising: a first solar cell that is a sequential stack, in the order recited, of an electrode, a silicon substrate, and an n-type emitter layer; a recombination layer disposed on the n-type emitter layer; an interfacial layer that is a double layer constituted of PEDOT:PSS and poly-TPD or PEDOT:PSS and PCDTBT, and that is disposed on the recombination layer; and a second solar cell that comprises a p-type hole selective layer and a perovskite layer disposed on the p-type hole selective layer, the p-type hole selective layer contacting and being integrated onto the interfacial layer in a heat treatment during which the interfacial layer is partially decomposed, wherein the presence of the interfacial layer prevents a reduction in photoelectric conversion efficiency that occurs if the first solar cell and the second solar cell are combined without the presence of the interfacial layer; and wherein the second solar cell is a sequential stack, in the order recited, of the p-type hole selective layer, the perovskite layer, an n-type electron selective layer, a transparent electrode layer, and a metal grid electrode layer; and wherein the second solar cell further comprises a protective oxide layer that is disposed between the n-type electron selective layer and the transparent electrode layer and is composed of zinc oxide, titanium dioxide, zirconium oxide, aluminum-doped zinc oxide, tin oxide, indium oxide, zinc tin oxide, niobium oxide, barium titanate, strontium titanate, tungsten oxide-titanium dioxide, or a mixture of two or more thereof.

2. The monolithic solar cell according to claim 1, wherein the perovskite layer is a composite material comprising groups selected from the group consisting of a group of carbon compounds comprising a methylammonium ion (CH.sub.3NH.sub.3.sup.+, MA ion) and a formamidinium ion (HC(NH.sub.2).sub.2.sup.+, FA ion), a group of metals comprising cesium, rubidium, lead, and tin, an iodine group, a chloride group, a halide group, and combinations thereof, and is manufactured by a solution process, a vacuum process, or a combined process.

3. The monolithic solar cell according to claim 1, wherein the p-type hole selective layer comprises NiO.sub.x, MoO.sub.x, V.sub.2O.sub.5, WO.sub.3, CuSCN or an oxide doped with at least one of Cu, Li, Mg, and Co.

4. The monolithic solar cell according to claim 1, wherein the n-type electron selective layer comprises PCBM, C.sub.60, or a combination thereof and comprises an organic layer composed of BCP, PFN, LiF, or PEIE.

5. The monolithic solar cell according to claim 1, wherein each of the recombination layer and the transparent electrode layer is a single layer comprising a material that is an oxide of indium, tin, zinc, and combinations thereof, aluminum zinc oxide, boron zinc oxide, or hydrogenated indium oxide, or that is selected from the group consisting of oxide-based nanoparticles, silver nanowires, carbon nanotubes, graphene, and PEDOT, or wherein each of the recombination layer and the transparent electrode layer is a composite layer wherein two or more materials of the materials form each layer of a double layer.

6. The monolithic solar cell according to claim 1, wherein the metal grid electrode layer comprises a metal selected from the group consisting of silver, gold, aluminum, and nickel or an alloy of two or more thereof.

Description

DESCRIPTION OF DRAWINGS

(1) FIG. 1 is a schematic diagram illustrating the configuration of a monolithic solar cell according to an embodiment of the present invention.

(2) FIG. 2 is a set of scanning electron microscope images and transmission electron microscope images illustrating the structure of a monolithic solar cell including an interfacial layer according to an embodiment of the present invention and the structure of a monolithic solar cell excluding an interfacial layer.

(3) FIG. 3 illustrates results of EDS line scan for element distribution near an interface between two cells in each of the case of a monolithic solar cell including an interfacial layer according to an embodiment of the present invention and the case of a monolithic solar cell excluding an interfacial layer.

(4) FIG. 4 illustrates results of XPS depth profile analysis for element distribution near an interface between two cells constituting a monolithic solar cell including an interfacial layer according to an embodiment of the present invention.

(5) FIG. 5 illustrates a current-voltage measurement graph for a monolithic solar cell and a schematic diagram of the measured monolithic solar cell in each of the case of a monolithic solar cell including an interfacial layer according to an embodiment of the present invention and the case of a monolithic solar cell excluding an interfacial layer.

(6) FIG. 6 illustrates a current-voltage measurement graph for a second solar cell, which is a perovskite solar cell, and a schematic diagram of the measured second solar cell in each of the case of a second solar cell including an interfacial layer according to an embodiment of the present invention and the case of a second solar cell excluding an interfacial layer.

(7) FIG. 7 illustrates current-voltage curves dependent upon a thickness change in a transparent electrode in a monolithic solar cell excluding an interfacial layer according to an embodiment of the present invention.

(8) FIG. 8 is a flowchart illustrating a procedure of a method of manufacturing a monolithic solar cell according to another embodiment of the present.

MODES OF THE INVENTION

(9) Hereinafter, the present invention will be described in detail with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. The features of the present invention will be more clearly understood from the accompanying drawings and should not be limited by the accompanying drawings, and it is to be appreciated that all changes, equivalents, and substitutes that do not depart from the spirit and technical scope of the present invention are encompassed in the present invention. To clearly explain the present invention, parts not related to the description are omitted in the drawings, and the size, form, and shape of each component shown in the drawings may be variously modified. Throughout this specification, the same or similar reference numerals are given to the same or similar parts. In the drawings, identical/like reference numerals denote identical/similar elements.

(10) Suffixes, “cell,” “step,” “process,” etc., for components used in the following description are given or used in combination in consideration of ease of specification writing and do not have a distinct meaning or role. In the following description of the present invention, a detailed description of known functions and configurations incorporated herein will be omitted when it may make the subject matter of the present invention unclear.

(11) In the specification, when it is described that a certain part is “connected, contacted, coupled, stacked, or laminated” to another part, it should be understood that the certain part may be directly “connected, contacted, coupled, stacked, or laminated” to another part or indirectly “connected, contacted, coupled, stacked, or laminated” to another part via another member in the middle. In addition, when a certain part “includes (is provided with)” a certain component, this indicates that the part may further “include (be provided with)” another component instead of excluding another component unless specifically described otherwise.

(12) It will be understood that, although the terms first, second, third etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element may be termed a second element and a second element may be termed a first element without departing from the teachings of the present invention.

(13) The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the inventive concept. The expression of singularity in the present specification includes the expression of plurality unless clearly specified otherwise in the context. Dispersed components may be implemented in a combined form unless otherwise specified. Also, the terms such as “include” or “comprise” may be construed to denote a certain characteristic, number, step, operation, component, or a combination thereof in the specification, but may not be construed to exclude the presence of or a possibility of addition of one or more other characteristics, numbers, steps, operations, components, or combinations thereof.

(14) FIG. 1 is a schematic diagram illustrating the configuration of a monolithic solar cell (hereinafter referred to as “monolithic solar cell 1”) according to an embodiment of the present invention. The monolithic solar cell 1 includes a first solar cell 100 forming a lower part of the monolithic solar cell 1, a second solar cell 200 formed on the first solar cell 100 and forming an upper part of the monolithic solar cell 1, and a junction layer 300 (or recombination layer) and interfacial layer 400 (or sacrificial layer) formed between the first and second solar cells 100 and 200.

(15) The first solar cell 100 is formed by sequentially stacking an electrode 110, a silicon substrate 120, and an n-type emitter layer 130 and may be a silicon solar cell excluding a front electrode.

(16) The junction layer 300 is formed on the n-type emitter layer 130 and may be a transparent conductive layer or transparent electrode layer with transparency and conductivity. The junction layer 300 may be formed of an oxide of at least one of indium (In), tin (Sn), and zinc (Zn), e.g., indium tin oxide, indium zinc oxide, or zinc tin oxide, aluminum zinc oxide, boron zinc oxide, or hydrogenated indium oxide including aluminum, boron, or hydrogen, or may be one layer or a composite layer including two or more selected from the group consisting of oxide-based nanoparticles, silver nanowires, carbon nanotubes, graphene, and PEDOT. The junction layer 300, which is a tunnel junction layer or a recombination layer, may be a layer for tandem integration of the first solar cell 100 and the second solar cell 200.

(17) The interfacial layer 400 may be formed on the junction layer 300 and may be a single layer constituted of conductive polymer-based PEDOT:PSS, PTAA, c-OTPD, PCDTBT, or, F4-TCNQ-doped PTAA or a double layer constituted of PEDOT:PSS and a polymer material (e.g., poly-TPD, PCDTBT, etc.), formed on the junction layer.

(18) In other words, the interfacial layer 400 may be a single layer constituted of poly(3,4-ethylenedioxy-thiophene) polystyrenesulfonate (PEDOT:PSS), poly(bis(4-phenyl)(2,4,6-trimethylphenyl)amine) (PTAA), polyvinyl alcohol (PVA), crosslinked N4,N4′-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4,N4′-diphenylbiphenyl-4,4′-diamine (c-OTPD), poly(N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7∝0-di-2-thienyl-2′,1′,3′-benzothiadiazole) (PCDTBT), or 2,3,5,6-Tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ)-doped PTAA, which are based on a conductive polymer, a double layer constituted of PEDOT:PSS and poly[N, N′-bis(4-butylphenyl)-N, N′-bis(phenyl)benzidine] (poly-TPD), or a double layer constituted of PEDOT:PSS and PCDTBT.

(19) In addition, the interfacial layer 400 may be partially decomposed in a process of integration of the first solar cell 100 to the second solar cell 200. Accordingly, the interfacial layer 400 may be referred to as an organic sacrificial layer.

(20) The second solar cell 200 with a perovskite included may be integrated on the interfacial layer 400 and formed in a perovskite solar cell form excluding a back electrode.

(21) In addition, the second solar cell 200 may have a form wherein a p-type hole selective layer 210, a perovskite layer 220, an n-type electron selective layer 230, a transparent electrode layer 240, and a metal grid electrode layer 250 are sequentially laminated.

(22) In addition, a protective oxide layer 260 formed of any one of zinc oxide, titanium dioxide, zirconium oxide (ZrO.sub.2), aluminum-doped zinc oxide (Al-doped ZnO), tin oxide (SnO.sub.2), indium oxide (In.sub.2O.sub.3), zinc tin oxide, niobium oxide (Nb.sub.2O.sub.5), barium titanate (BaTiO.sub.3), strontium titanate (SrTiO.sub.3), or tungsten oxide-titanium dioxide (WO.sub.x—TiO.sub.x) or a mixture of two or more thereof may be further included between the n-type electron selective layer 230 and the transparent electrode layer 240 of the second solar cell 200.

(23) The perovskite layer 220 constituting the second solar cell 200 may be formed of a composite material formed by combining two or more groups selected from the group consisting of a group of carbon compounds including a methylammonium ion (CH.sub.3NH.sub.3.sup.+, MA ion) and a formamidinium ion (HC(NH.sub.2).sub.2.sup.+, FA ion), a group of metals including cesium, rubidium, lead, and tin, an iodine group, a chloride group, and a halide group, but the present invention is not limited thereto. In addition, the perovskite layer 220 may be manufactured by a solution process, a vacuum process, or a combined process, but the present invention is not limited thereto.

(24) In addition, the p-type hole selective layer 210 may be formed of any one of NiO.sub.x, MoO.sub.x, V.sub.2O.sub.5, WO.sub.3, and CuSCN or an oxide doped with at least one of Cu, Li, Mg, and Co, and the n-type electron selective layer 230 may be formed of any one of PCBM and C.sub.60 or a combination thereof, but the present invention is not limited thereto. In addition, the n-type electron selective layer 230 may include a separate organic layer formed of BCP, PFN, LiF, or PEIE.

(25) Similar to the junction layer 300 described above, the transparent electrode layer 240 may also be formed of an oxide of at least one of indium (In), tin (Sn), and zinc (Zn), e.g., indium tin oxide, indium zinc oxide, or zinc tin oxide, aluminum zinc oxide, boron zinc oxide, or hydrogenated indium oxide including aluminum, boron, or hydrogen, or may be one layer or a composite layer including two or more selected from the group consisting of oxide-based nanoparticles, silver nanowires, carbon nanotubes, graphene, and PEDOT.

(26) In other words, each of the junction layer 300 and the transparent electrode layer 240 may be a single layer formed of an oxide of at least one of indium, tin, and zinc, any one of aluminum zinc oxide, boron zinc oxide, and hydrogenated indium oxide, or one material selected from the group consisting of oxide-based nanoparticles, silver nanowires, carbon nanotubes, graphene, and PEDOT, or a composite layer wherein two or more materials of the materials form each layer of a double layer.

(27) The metal grid electrode layer 250 may be formed of any one metal of silver, gold, aluminum, and nickel or an alloy of two or more thereof, or may be formed of various types of metals or alloys.

(28) Hereinafter, effects of the monolithic solar cell 1 will be described in detail through an experimental example, in which the monolithic solar cell 1 manufactured according to an embodiment of the present invention was used, and a comparative example of the experimental example, with reference to FIGS. 2 to 7.

Experimental Example

(29) To manufacture monolithic solar cells including an interfacial layer (organic sacrificial layer) according to various embodiments of the present invention, a first solar cell, which was a silicon solar cell type, was prepared, an ITO-type tunnel junction layer was formed on an n-type emitter of the first solar cell, a PEDOT:PSS interfacial layer (or organic sacrificial layer) was formed on the ITO-type tunnel junction layer, and a second solar cell, which was a perovskite solar cell type, was laminated on the PEDOT:PSS interfacial layer.

(30) Here, the PEDOT:PSS interfacial layer was manufactured by diluting PEDOT:PSS (Clevios™ P VP AI 4083), manufactured by Heraeus, with methanol, and then forming a PEDOT:PSS thin-film by spin-coating, followed by heat-treatment at 150° C. for 20 minutes.

(31) A second solar cell, which is a perovskite solar cell type, was manufactured by sequentially laminating a p-type hole-selective film, a perovskite, an n-type electron-selective film, a protective oxide layer, a transparent electrode, and a metal grid electrode from the bottom.

(32) To produce the p-type hole-selective film, nickel nitrate hexahydrate, cupric nitrate trihydrate, and ethylenediamine were dissolved in ethylene glycol at a concentration of 1.0 M, and then a nickel oxide precursor film was formed by spin-coating, followed by oxidizing at 300° C. for 1 hour, thereby manufacturing a nickel oxide-based hole-selective film doped with 5 mol % copper.

(33) The perovskite was manufactured by a one-step process using methylammonium iodide (CH.sub.3NH.sub.3I) and lead iodide (PbI.sub.2) (methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3)). Here, methylammonium lead iodide (CH.sub.3NH.sub.3PbI.sub.3) is one of compositions of a perovskite light absorption layer and may be named MAPbI.sub.3.

(34) Each of the n-type electron-selective film and the protective oxide layer was formed by spin-coating each of PCBM and ZnO solutions, an InZnO-type transparent electrode was formed by sputter deposition, and an Ag grid electrode was deposited by a thermal evaporation method.

(35) The structure of the monolithic solar cell including the PEDOT:PSS interfacial layer was observed with a field emission scanning electron microscope (FE-SEM, Inspect F) and a transmission electron microscope (TEM, TITAN), and results thereof are illustrated in FIG. 2 (FIG. 2(a)). In addition, to analyze the PEDOT:PSS interfacial layer in detail, EDS line scan (energy dispersive X-ray spectroscopy, Talos) analysis and XPS depth profile (PHI 5000 VersaProbe) analysis were performed, and results thereof are respectively illustrated in FIGS. 3 and 4.

(36) Referring to FIG. 3, a small amount of the sulfur (S) component contained in PEDOT:PSS was detected near the interface between the two cells constituting the monolithic solar cell including the interfacial layer. On the other hand, referring to FIG. 4, it can be confirmed that an XPS signal of PEDOT:PSS is not detected at the interface between the two cells constituting the monolithic solar cell including the interfacial layer.

(37) From these results, it can be confirmed that the very thin PEDOT:PSS interfacial layer is partially or completely pyrolyzed and lost during the high-temperature heat treatment process to manufacture the nickel oxide-based hole-selective film, thus is a sacrificial layer.

(38) Meanwhile, referring to a current-voltage curve of each of the monolithic solar cells including or excluding the interfacial layer shown in FIG. 5, it can be confirmed that photoelectric conversion efficiency of the monolithic solar cell including the interfacial layer is significantly improved. In particular, it can be confirmed that the significant decrease in series resistance is a major factor in improving the performance of the solar cell.

(39) As shown in the experimental example, it can be confirmed that, although the PEDOT:PSS interfacial layers according to the various embodiments of the present invention are pyrolyzed and thus partially or completely lost during a monolithic solar cell manufacturing process, the interface between the two cells constituting the monolithic solar cell exhibits significantly improved charge transfer or recombination characteristics, compared to a conventional monolithic solar cell, due to insertion of the interfacial layer (sacrificial layer). Accordingly, the present invention can provide a monolithic solar cell with dramatically improved photoelectric conversion efficiency. In addition, introduction of the appropriate interfacial layer according to the various embodiments of the present invention allows a monolithic solar cell to minimize factors causing efficiency loss that occurs at an interface or a junction between two subcells, enabling the implementation of a highly efficient monolithic solar cell.

Comparative Example 1

(40) Second solar cells, which are single-junction perovskite solar cell types, were manufactured while excluding a first solar cell, which is a silicon solar cell, thereunder in the same manner as in the experimental example. One of the second solar cells was manufactured to include a PEDPOT:PSS interfacial layer on an ITO transparent electrode substrate, and another second solar cell was manufactured to exclude the PEDPOT:PSS interfacial layer. Schematic diagrams and current-voltage measurement results of the second solar cells are illustrated in FIG. 6.

(41) Referring to FIG. 6, it can be confirmed that the presence of the PEDOT:PSS interfacial layer does not greatly affect the performance of the second solar cells which are single-junction perovskite solar cell types. From this, it can be confirmed that, when the properties of the ITO transparent electrode formed on the first solar cell, which is a silicon solar cell type, to manufacture a monolithic solar cell are different from the properties of the ITO transparent electrode used to manufacture the second solar cell which is a single-junction perovskite solar cell type, charge transfer or recombination between two cells constituting the monolithic solar cell may not be smoothly performed.

Comparative Example 2

(42) A monolithic solar cell was manufactured in the same manner as in the aforementioned experimental example, except that a PEDOT:PSS interfacial layer was not inserted thereinto. The structure of the monolithic solar cell according to Comparative Example 2 was observed, and a result thereof is illustrated in FIG. 2(b).

(43) Referring to FIG. 2(b), it can be confirmed that the presence of the PEDOT:PSS interfacial layer does not affect the structure of the upper layers, compared to the image of FIG. 2(a) illustrating the structure according to the aforementioned experimental example. Accordingly, it can be confirmed that the structural characteristics of the monolithic solar cells manufactured according to the various embodiments of the present invention are not affected by insertion of the PEDOT:PSS interfacial layer.

(44) Meanwhile, referring to FIG. 7 illustrating a current-voltage measurement graph of the monolithic solar cell excluding the interfacial layer manufactured according to Comparative Example 2 in the same manner as in the aforementioned experimental example, it can be confirmed that the monolithic solar cell has a high series resistance regardless of the thickness of the ITO transparent electrode formed on the first solar cell, which is a silicon solar cell type, while exhibiting a high open-circuit voltage, whereby a fill factor and photoelectric conversion efficiency thereof are significantly decreased. It can be assumed that the very high series resistance of the monolithic solar cell manufactured according to Comparative Example 2 is caused by a junction between the two cells because the monolithic solar cell manufactured according to the experimental example is the same as the monolithic solar cell manufactured according to Comparative Example 2 except for the presence/absence of the interfacial layer. FIG. 8 is a flowchart illustrating a method of manufacturing the monolithic solar cell according to another embodiment of the present invention (hereinafter referred to as “monolithic solar cell manufacturing method (2)”. A monolithic solar cell (1), which has been described above with reference to FIGS. 1 to 7, may be manufactured by a monolithic solar cell manufacturing method (2) described below. Accordingly, contents overlapping with the above-mentioned contents are omitted.

(45) The monolithic solar cell manufacturing method (2) includes a step (S100) of forming a junction layer (or recombination layer), which is a transparent electrode type, on a first solar cell formed by sequentially stacking an electrode, a silicon substrate, and an n-type emitter layer, a step (S200) of forming an interfacial layer (or sacrificial layer) on the junction layer, and a step of forming a second solar cell including a perovskite layer on the interfacial layer.

(46) In S100, a heat treatment process and an ozone treatment process, such as a UV-ozone process, and the like may be performed.

(47) In addition, S100 is a step of forming an single interfacial layer, constituted of PEDOT:PSS, PTAA, c-OTPD, PCDTBT, or, F4-TCNQ-doped PTAA, on the junction layer or a step of forming a double interfacial layer, constituted of PEDOT:PSS and a polymer material (e.g., poly-TPD, PCDTBT, etc.), on the junction layer.

(48) Here, the first solar cell, the junction layer, the interfacial layer, and the second solar cell may be the same as those described above.

(49) In addition, S100 to S300 constituting the monolithic solar cell manufacturing method (2) are not required to be necessarily performed in the order of S100, S200, and S300. The monolithic solar cell manufacturing method (2) may be performed through various procedures, and S100 to S300 may be almost simultaneously performed.

(50) When the interfacial layer is formed and then the second solar cell is laminated according to the various embodiments of the present invention, the interfacial layer is partially or completely pyrolyzed and removed by the heat treatment step of the manufacturing processes of the second solar cell. However, an interface between two cells constituting the monolithic solar cell that includes a sacrificial layer, such as the interfacial layer, formed on the first solar cell and the second solar cell integrated to the sacrificial layer manufactured according to the various embodiments of the present invention in this manner can exhibit considerably improved charge transfer or recombination characteristics, compared to that of the monolithic solar cell excluding the interfacial layer. Accordingly, a tandem-type monolithic solar cell having dramatically improved photoelectric conversion efficiency can be manufactured.

(51) The aforementioned description of the present invention is provided by way of example and those skilled in the art will understand that the present invention can be easily changed or modified into other specified forms without change or modification of the technical spirit or essential characteristics of the present invention. Therefore, it should be understood that the aforementioned examples are only provided by way of example and not provided to limit the present invention. It should be understood that the scope of the present invention is defined by the following claims and the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.

MODE FOR CARRYING OUT THE INVENTION

(52) Embodiments for carrying out the invention are described together in the best mode for carrying out the invention.

INDUSTRIAL APPLICABILITY

(53) The present invention relates to a monolithic solar cell and a method of manufacturing the same. The monolithic solar cell and the method according to the present invention can be applied to a solar cell manufacturing technology and repetitively performed, thus having industrial applicability.

(54) It will be apparent to those skilled in the art that various modifications can be made to the above-described exemplary embodiments of the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers all such modifications provided that they come within the scope of the appended claims and their equivalents.