SIMPLIFIED STRUCTURE OF TWO-TERMINAL TANDEM SOLAR CELLS WITH TRANSPARENT CONDUCTING OXIDE JUNCTION MATERIAL

Abstract

A tandem photovoltaic structure including, from the rear face to the front face: a first SHJ solar cell comprising a first layer of P-type doped amorphous silicon and a substrate of N-type doped crystalline silicon, a junction layer, a second perovskite-type solar cell comprising an active layer and a second P-type layer, the junction layer being made of N-type TCO and being in direct contact either with the second P-type layer or with the first P-type layer, one amongst the first or second solar cell also comprising an N-type layer, the junction layer serving as an N-type layer in the other one amongst the first or second solar cell.

Claims

1. A 2-terminal PIN-type tandem photovoltaic structure comprising, from the rear face to the front face: a first solar cell with a silicon heterojunction comprising a first P-type layer made of doped amorphous silicon and a substrate of N-type doped crystalline silicon disposed between a first layer of intrinsic amorphous silicon and a second layer of intrinsic amorphous silicon, a junction layer, a second perovskite-type cell comprising a second P-type layer, an active layer made of a perovskite material and an N-type layer, wherein the junction layer is made of a transparent conductive oxide, and wherein the junction layer is in contact with the second layer of intrinsic amorphous silicon of the first solar cell and with the second P-type layer of the second solar cell, the junction layer serving as an N-type layer in the first solar cell.

2. The tandem structure according to claim 1, wherein the junction layer is made of ITO.

3. The tandem structure according to claim 1, wherein the junction layer is made of AZO, ZnO, IWO, IZO, IZrO or SnO.sub.2-x with x greater than 0 and strictly less than 2.

4. The tandem structure according to claim 1, wherein the junction layer has a thickness from 2 to 30 nm and preferably between 2 nm and 15 nm.

5. The tandem structure according to claim 1, wherein the junction layer has a conductivity higher than 10 S.Math.cm.sup.?1.

6. The tandem structure according to claim 1, wherein the tandem structure comprises from the rear face to the front face: the first solar cell with a silicon heterojunction based on amorphous silicon and crystalline silicon comprising, from the rear face to the front face: the first P-type layer made of doped amorphous silicon, the first layer of intrinsic amorphous silicon, the substrate of N-doped crystalline silicon and the second layer of intrinsic amorphous silicon, the junction layer made of N-type TCO, the second perovskite-type solar cell comprising, from the junction material to the front face: a P-type layer, made of PTAA or TFB, the active layer made of a perovskite material and an N-type layer made of SnO.sub.2 or formed by a PCBM/SnO.sub.2 bilayer.

7. The tandem structure according to claim 1, wherein the perovskite material has the formula Cs.sub.xFA.sub.1-xPb(I.sub.1-yBr.sub.y).sub.3 (with x<0, 20; 0<y<1).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0048] The present invention will be better understood upon reading the description of embodiments given merely for informative and non-limiting purposes with reference to the appended drawings wherein:

[0049] FIG. 1A already discussed in the prior art, represents, schematically and in section, a two-terminal NIP-type tandem structure.

[0050] FIG. 1B already discussed in the prior art, represents, schematically and in section, a two-terminal PIN-type tandem structure.

[0051] FIG. 2A represents, schematically and in section, a simplified two-terminal NIP-type tandem structure, according to a particular embodiment of the invention.

[0052] FIG. 2B represents, schematically and in section, a simplified two-terminal PIN-type tandem structure, according to another particular embodiment of the invention.

[0053] FIGS. 3A, 3B and 3C are graphs representing the EQE and the 1-Rtot value as a function of the wavelength (with Rtot corresponding to the total reflection of the stack of the cell (without the metallisation at the front face), obtained by optical simulation for tandem structures with a PIN or NIP type thin (12 nm) junction made of ITO, and having, respectively either two polished faces, or one textured rear face or both faces textured; ref corresponds to conventional tandem structures and simp to simplified tandem structures, according to particular embodiments of the invention; the simplified tandem structures differ from the conventional structures by the absence of a layer with a N polarity in one of the sub-cells.

[0054] The different portions represented in the figures are not necessarily plotted according to a uniform scale, to make the figures more readable.

[0055] In the description hereinafter, terms that depend on the orientation, such as top/upper, bottom/lower, etc. of a structure apply while considering that the tandem device and the test structure are oriented as illustrated in the figures.

DETAILED DISCLOSURE OF PARTICULAR EMBODIMENTS

[0056] First of all, reference is made to FIGS. 2A and 2B which represent simplified tandem structures 100.

[0057] The tandem structures 100 comprise from the rear face to the front face (i.e. the face intended to receive the light radiation represented by the arrows) a multilayer stack forming: [0058] a first cell 110 (or lower cell for bottom cell) with a silicon heterojunction (HET-Si or SHJ standing for Silicon HeteroJunction solar cell) based on amorphous silicon and crystalline silicon, positioned at the rear face, [0059] a junction layer 120 made of a transparent conductive oxide (also called junction and recombination layer), intended to electrically contact the two sub-cells of the tandem structure 100 and enabling the charges to recombine, [0060] a second perovskite-type cell 130 (or upper cell for top cell) positioned at the front face.

[0061] The tandem structure 100 may be a NIP-type (FIG. 2A) or PIN-type (FIG. 2B) structure.

[0062] More particularly, the NIP-type (or with a standard emitter) structure comprises from the rear face to the front face (FIG. 2A): [0063] a first solar cell 110 with a silicon heterojunction; based on amorphous silicon and crystalline silicon; and comprising from the rear face to the front face: a layer of N-doped amorphous silicon (also called layer of n-doped hydrogenated amorphous silicon and also denoted (n) a-Si:H) 111, a substrate of doped crystalline silicon 112 (typically a substrate of n-doped crystalline silicon also denoted c-Si (n)) disposed between two layers of intrinsic amorphous silicon 113, 114 (also called layers of (i) a-Si:H or intrinsic hydrogenated amorphous silicon), and a layer of P-doped amorphous silicon (also denoted (p) a-Si:H for p-doped hydrogenated amorphous silicon) 115, [0064] a junction layer 120 made of N-type transparent conductive oxide (also known by the acronym TCO), [0065] a second perovskite-type solar cell 130 comprising, from the junction layer 120 to the front face, an active layer 131 made of a perovskite material and a P-type layer 132,

[0066] For this NIP-type structure, the active layer 131 of the second cell 130 is directly in contact with the junction layer 120, it therefore has no layer interposed between the two.

[0067] More particularly, the PIN-type (or with an inverted emitter) structure comprises from the rear face to the front face (FIG. 2B) a multilayer stack forming: [0068] a first solar cell 110 with a silicon heterojunction based on amorphous silicon and crystalline silicon comprising from the rear face to the front face: a layer 115 of P-doped amorphous silicon ((p) a-Si:H), a first layer 113 of intrinsic amorphous silicon ((i) a-Si:H), a substrate 112 of N-type doped crystalline silicon (substrate c-Si (n)) and a second layer 114 of intrinsic amorphous silicon ((i) a-Si:H), [0069] a junction layer 120 made of TCO [0070] a second perovskite-type solar cell 130 comprising from the junction layer to the front face: a P-type layer 132, an active layer 131 made of a perovskite material, an N-type layer 133.

[0071] For this PIN-type structure, the second layer 114 of intrinsic amorphous silicon of the first cell 110 is directly in contact with the junction layer 120; it therefore has no layer interposed between the two.

[0072] In these different variants, the junction layer 120 made of TCO may have a thickness of 2 to 30 nm and preferably between 2 nm and 15 nm.

[0073] For example, the conductivity of the junction layer 120 made of TCO is higher than 10 S.Math.cm.sup.?1.

[0074] The junction layer 120 may be made of indium-tin oxide (ITO), zinc oxide (ZnO), aluminium-doped zinc oxide (AZO), indium-tungsten oxide (IWO), indium-zinc oxide (IZO), zirconium-doped indium oxide (IZrO) or tin dioxide (SnO.sub.2-x with 0<x<2).

[0075] The band gap of the junction layer 120 made of TCO ranges from 2.8 to 4 eV.

[0076] The junction layer 120 made of ITO has a conduction band from ?4.2 to ?5.2 eV. For the other aforementioned doped oxides, the conduction band ranges from ?4 to ?5.2 eV.

[0077] Preferably, the junction layer 120 is made of ITO.

[0078] The silicon substrate 12 of the lower cell may be polished or textured (for example, it may consist of texturing in the form of 2 ?m pyramids). The amorphous layers of the lower cell having a thickness of a few nanometres, they will take on the shape of the texturing of the substrate.

[0079] For example, the p/n type doping levels of the layers 111 and 115 are between 10.sup.18 and 10.sup.19/cm.sup.3.

[0080] The N-type layer 133 of the second perovskite cell is called electron transport layer (or EIL standing for Electron Injection Layer or ETL standing for Electron Transport Layer).

[0081] For example, the N-type layer 133 is a metal oxide such as zinc oxide (ZnO), aluminium-doped zinc oxide also called AZO (ZnO:Al), titanium oxide (TiO.sub.2) or tin oxide (SnO.sub.2). It may also consist of a stack of methyl [6,6]-phenyl-C.sub.61-butanoate and of SnO.sub.2 (PCBM/SnO.sub.2) or of methyl [6,6]-phenyl-C.sub.61-butanoate and of bathocuproine (PCBM/BCP).

[0082] The perovskite material of the active layer 131 of the second solar cell 130 has the general formula ABX.sub.3 with A representing one or more monovalent organic cation(s), such as an ammonium, like methylammonium or formamidinium, or a monovalent metal cation, like cesium or rubidium; B representing a divalent metal cation like Pb, Sn, Ag or a mixture thereof; and X representing one or more halide anion(s).

[0083] More particularly, the perovskite material may have the particular formula H.sub.2NCHNH.sub.2PbX.sub.3 or CH.sub.3NH.sub.3PbX.sub.3 with X a halogen. For example, it may consist of methylammonium lead iodide CH.sub.3NH.sub.3PbI.sub.3. Preferably, the perovskite material has the formula Cs.sub.xFA.sub.1-xPb(I.sub.1-yBr.sub.y).sub.3.

[0084] The P-type layer 132 of the second cell 130 is also called hole transport layer (or HTL standing for Hole Transport Layer).

[0085] For example, the P-type layer 132 is an organic compound like Poly(3,4-ethylenedioxythiophene) Polystyrene sulfonate (PEDOT:PSS), [poly(bis 4-phenyl}{2,4,6-trimethylphenyl}amine)] (PTAA), [Poly(N,N-bis(4-butylphenyl)-N,N-bis(phenyl)-benzidine] (Poly-TPD), 2,2,7,7-Tetrakis[N,N-di(4-methoxyphenyl)amino]-9,9-spirobifluorene (spiro-OMeTAD), N4,N4-bis(4-(6-((3-ethyloxetan-3-yl)methoxy)hexyl)phenyl)-N4,N4-diphenyl-[1,1-biphenyl]-4,4-diamine (OTPD), poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(4,4-(N-(4-sec-butylphenyl)diphenylamine)] (TFB) or pyrene, or else a metal oxide such as a molybdenum oxide, a vanadium oxide or a tungsten oxide.

[0086] It could also be obtained from phosphate(s), silanes or carboxylic acids.

[0087] The tandem structure 100 may also comprise: [0088] a first electrode 140 (lower electrode) disposed at the rear face; the lower electrode 140 may, advantageously, be opaque or of limited transparency, for example a transparent conductive oxide such as in particular ITO, IOH (hydrogenated indium oxide), or AZO, [0089] a second electrode 150 (upper electrode) disposed over the front face of the device; the second electrode is electrically-conductive and optically-transparent, so as to let the photons pass up to the active layer 131 of the upper cell 130. This electrode 150 may be made of a transparent conductive oxide, typically indium-tin oxide (ITO) or aluminium-doped zinc oxide (ZnO:Al), or it may be formed of a transparent conductive polymer comprising silver nanowires for example, [0090] contact pads 160 at the rear face and contact pads 170 at the front face; the contact pads may for example be made of gold, aluminium or silver (deposited for example by evaporation, or printed by screen-printing, inkjet printing, etc.).

Illustrative and Non-Limiting Examples of One Embodiment

[0091] Optical simulations of different structures have been carried out using the CROWM software, while taking into account the optical indices of the layers, their thickness and the surface condition (completely flat, textured, etc.). These simulations are performed between 310 and 1,200 nm with the AM1.5 solar spectrum. The optical indices have been extracted by ellipsometry from the experimental layers.

[0092] Table 1 lists the thicknesses (nm) of the simulated layers for the NIP-type architectures.

TABLE-US-00001 NIP reference NIP simplified structure structure ITO front face 180 180 PTAA 30 30 Perovskite 250 and 415 250 and 415 SnO.sub.2 30 Junction layer made of rec. ITO 12 12 a-Si:H (p) 19 19 a-Si:H (i) 5 5 c-Si 280000 280000 a-Si:H (i) 5 5 a-Si:H (n) 8 8 ITO rear face 70 70 Ag 200 200

[0093] Table 2 lists the thicknesses (nm) of the simulated layers for the PIN-type architectures.

TABLE-US-00002 NIP reference NIP simplified structure structure ITO front face 180 180 SnO.sub.2 30 30 Active layer made of perovskite 250 and 415 250 and 415 PTAA 30 30 Junction layer made of rec. ITO 12 12 a-Si:H (n) 8 a-Si:H (i) 5 5 c-Si 280000 280000 a-Si:H (i) 5 5 a-Si:H (p) 19 19 ITO rear face 70 70 Ag 200 200

[0094] The perovskite used in the simulations is of the Cs.sub.xFA.sub.1-xPb(I.sub.1-yBr.sub.y).sub.3 type (with x<0.20; 0<y<1), two different thicknesses have been used to obtain less current discrepancy between the two sub-cells when the surface condition is modified.

[0095] FIGS. 3A, 3B and 3C represent the EQE and 1-Rtot values obtained by optical simulations for the different tandem structures of Tables 1 and 2.

[0096] The disclosed results correspond to tandem structures wherein the active layer of the upper cell is a perovskite material that is 250 nm thick when the front face is polished and 415 nm thick when it is textured.

[0097] This optical simulation study demonstrates that simplified NIP and PIN tandem structures with a junction made of ITO are viable regardless of texturing. Indeed, these simplified structures have only very few differences from an optical perspective with conventional complete structures and have the same optical potential.

[0098] In addition, the following Table 3 lists the values of J.sub.sc and R.sub.tot obtained by optical simulations, the estimated PCEs for FF=75% and V.sub.oc=1.8 V. This table shows that the resulting short-circuit currents are quite similar.

TABLE-US-00003 J.sub.sc PK J.sub.sc Si PCE R.sub.tot Front face Rear face NIP/PIN FIG. (mA/cm.sup.2) (mA/cm.sup.2) (%) (mA/cm.sup.2) Reference tandem structure polished textured NIP 1A 16.95 16.58 22.38 9.2 polished textured PIN 1B 16.93 16.79 22.67 9.69 polished polished NIP 1A 16.95 15.79 21.32 11.41 polished polished PIN 1B 16.93 16.09 21.72 11.83 textured textured NIP 1A 19.67 20 26.55 2.9 textured textured PIN 1B 19.99 20.1 26.99 3.06 Simplified tandem structure polished textured NIP 2A 16.58 17.16 22.38 8.73 polished textured PIN 2B 16.91 16.88 22.79 9.67 polished polished NIP 2A 16.58 16.36 22.09 11.18 polished polished PIN 2B 16.91 16.13 21.78 11.85 textured textured NIP 2A 19.42 20.32 26.22 2.69 textured textured PIN 2B 19.99 20.12 26.99 3.05