Back contacts materials used in thin film CdTe solar cells—A review

Hall, R. S.; Lamb, David; Irvine, S.J.C.

doi:10.1002/ese3.843

Cited by 45 publications

(43 citation statements)

References 227 publications

(202 reference statements)

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“…On the other hand, stable n-type doping up to n = 10 18 cm −3 has been demonstrated using indium [28], this being close to the degenerate doping density and comfortably exceeding the levels required in PV devices. Secondly, contacting is a well-known issue for p-CdTe [29], and may create a back-contact barrier (from band line ups [30] or Fermi level pinning [31]) which limits the forward bias current of the devices [32]. Strategies, such as using ZnTe:Cu [33], are required to mitigate this barrier by supplying high local p-doping near the contact.…”

Section: Introductionmentioning

confidence: 99%

“…Strategies, such as using ZnTe:Cu [33], are required to mitigate this barrier by supplying high local p-doping near the contact. Nevertheless, contacting to p-CdTe solar cells is found to be universally problematic, and a recent review identified more than 70 different strategies for making the contacts [29]. Whatever the origin of the difficulties for contacting p-CdTe, they are not an issue with n-type material, for which indium is known to give a low-resistance Ohmic contact [34,35].…”

Section: Introductionmentioning

confidence: 99%

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Insights into post-growth doping and proposals for CdTe:In photovoltaic devices

Thomas¹,

Hobson²,

Phillips³

et al. 2022

J. Phys. Energy

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This paper is motivated by the potential advantages of higher doping and lower contact barriers in CdTe photovoltaic devices that may be realized by using n- type rather than the conventional p-type solar absorber layers. We present post-growth doping trials for indium in thin polycrystalline CdTe films using diffusion of indium metal and with indium chloride. Chemical concentrations of indium up to 1019 cm-3 were achieved and the films were verified as n-type by hard x-ray photoemission. Post growth chlorine treatment (or InCl3) was found to compensate the n-doping. Trial structures comprising CdS/CdTe:In verified that the doped absorber structures performed as expected both before and after chloride treatment, but it is recognized that this is not an optimum combination. Hence in order to identify how the advantages of n-type absorbers might be fully realized in future work, we also report simulations of a range of p-n junction combinations with n-CdTe, a number of which have the potential for high Voc.

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Insights into post-growth doping and proposals for CdTe:In photovoltaic devices

Thomas¹,

Hobson²,

Phillips³

et al. 2022

J. Phys. Energy

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“…Therefore, back contacts with high metal work functions are economically viable materials for solar cell designs. 43 Accordingly, lower efficiencies are recorded when the metal work functions of the back contact are low since there exist high-energy Schottky barriers. Back contacts with metal work functions above 5.1 eV are considered robust for better cell performance.…”

Section: Effect Of Metal Work Function On Cell Performancementioning

confidence: 99%

“…Notably, carbon/nickel (5.0 eV) and palladium (5.3 eV) are feasible candidates for back contacts since their metal work functions are sufficiently high energy to minimize Schottky barriers, hence high PV performance. 43 Therefore, this study proposes the use of carbon/nickel (5.0 eV) and palladium (5.3 eV) as dye regenerating candidates in ssDSSCs because of their decent work functions in addition to economic viability.…”

Section: Effect Of Metal Work Function On Cell Performancementioning

confidence: 99%

Computational Simulation of a Highly Efficient Hole Transport-Free Dye-Sensitized Solar Cell Based on Titanium Oxide (TiO2) and Zinc Oxysulfide (ZnOS) Electron Transport Layers

Korir

Kibet

Ngari

2021

J. Electron. Mater.

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In order to mitigate the current global energy and environmental challenges associated with the use of fossil fuels, there is a need for better energy alternatives such as the inexhaustible solar energy. Of great interest is the design and fabrication of low-cost photovoltaic devices which are the epitome of efficient solar energy harvesting. Herein, we report inexpensive hole transport layer (HTL)-free dye-sensitized solar cell architecture with robust photovoltaic (PV) performance. In the proposed solar cell model, expensive hole transport layers, CuI, CuSCN, Spiro-OMeTAD, and PEDOT:PSS, are not required, but instead, a metallic layer is used for dye regeneration. A thorough analysis of the effect of series and shunt resistances, conduction band offset, Schottky barriers, working temperature, the metal work function of the back contact, and the electron affinities of the electron transport layers (ETLs) on the performance of the proposed solar cell is presented. The Solar Capacitance Simulator (SCAPS-1D) is used to perform the numerical simulations of the proposed solar cell design. The study focused on modeling HTL-free dye-sensitized solar cells with the configuration: FTO/ETL/N719 dye/Au. The performance of two ETLs-ZnOS and TiO 2 are critically examined. The optimized model cell performance for the FTO/ZnOS/N719 dye/Au architecture gave an optimal power conversion efficiency (PCE) of 11.54%, 62.71% as the fill factor (FF), short circuit current (Jsc) of 18.50 mAcm −2 , and an open-circuit voltage (Voc) of 0.99 V. On the other hand, the cell architecture FTO/TiO 2 / N719 dye/Au gave an optimized performance of 10.22% as the PCE, 63.58% as the FF, a Voc of 0.97 V, and 16.50 mAcm −2 as the Jsc. Based on these results, ZnOS is a suitable ETL material that has better PV performance of the solar cell device under consideration. ZnOS is earth-abundant, has a tunable band gap, is less toxic, and is, therefore, a promising candidate to replace TiO 2 ETL in future designs and manufacture of HTL-free DSSCs for commercial production.

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“…[3,12] Other Cu-containing materials that have been considered as back contacts include Cu x Te, [13] Cu x S, [14] HgTe:Cu, CuI, CuSCN, and Cu x Zn 1−x S. [13,14,15] Copper is commonly used to dope CdTe p-type in the 10 14 -10 15 cm −3 range. [8] The Cu ions in the back contacts, including ZnTe:Cu, are known to diffuse into CdTe, and substitute Cd to form shallow acceptor states (p-type doping). However, "excess" Cu in CdTe is also associated with metastability and long-term performance degradation, including changes in the series resistance and fill factor.…”

Section: Introductionmentioning

confidence: 99%

A Search for New Back Contacts for CdTe Solar Cells

Gorai

Krasikov

Grover

et al. 2022

Preprint

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There is widespread interest in reaching the practical efficiency of cadmium telluride (CdTe) thin-film solar cells, which suffer from significant open-circuit voltage loss due to high surface recombination velocity and Schottky barrier at the back contact. Here, we focus on back contacts in the superstrate configuration with the goal of finding new materials, that can provide improved passivation, electron reflection and hole transport properties compared to the commonly used material, ZnTe. We performed a computational search among 229 binary and ternary tetrahedrally-bonded structures using first-principles methods and transport models to evaluate critical materials design criteria, including phase stability, electronic structure, hole transport, band alignments, and p-type dopability. Through this search, we have identified several candidate materials and their alloys (AlAs, AgAlTe2, ZnGeP2, ZnSiAs2, CuAlTe2) that exhibit promising properties for back contacts. We hope these new material recommendations and associated guidelines will inspire new directions in hole transport layer design for CdTe solar cells.

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Back contacts materials used in thin film CdTe solar cells—A review

Abstract: This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

Cited by 45 publications

References 227 publications

Insights into post-growth doping and proposals for CdTe:In photovoltaic devices

Insights into post-growth doping and proposals for CdTe:In photovoltaic devices

Computational Simulation of a Highly Efficient Hole Transport-Free Dye-Sensitized Solar Cell Based on Titanium Oxide (TiO2) and Zinc Oxysulfide (ZnOS) Electron Transport Layers

A Search for New Back Contacts for CdTe Solar Cells

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