Thin-film photovoltaic (PV) solar cells based on CdTe and Cu(In,Ga)Se2 (CIGS) have reached power conversion efficiencies above 21% at the laboratory scale, while module performance can rival those of Si technology. However, the overall market share of these technologies can potentially be compromised by material availability and costs considering the current exponential expansion of PV installed capacity worldwide. Cu2ZnSn(S,Se)4 (CZTSSe) is one of the most promising candidates for replacing CIGS, with recent reports showing champion cells above 13%. Significant efforts have been devoted to developing high quality (CZTSSe) thin-films by physical vapour deposition and solution based methods. The latter approach is rather attractive for large-scale module production with low capital costs. In this contribution, we will describe a methodology for generating high quality CZTSSe film initiated by depositing a precursor solution containing metal chlorides and thiourea in dimethyl formamide onto Mo coated glass, followed by thermal annealing under Se atmosphere. Devices with the architecture Mo/CZTSSe/CdS/i-ZnO/Al:ZnO are fabricated with total area of 0.25 cm2. The performances of 20 devices are assessed under AM1.5G illumination with the best device featuring a short-circuit current of 27.8 mA/cm2, open-circuit voltage of 396 mV, fill factor of 52 % and power conversion efficiency of 5.7 %. From analysis of variable temperature photoluminescence of the CTZSSe films and electrical impedance of the devices, we can identify the chemical nature of bulk acceptor states that may contribute to bulk recombination losses. In addition, detailed analysis of photoemission microscopy uncovered a complex work-function landscape of the CZTSSe films, which allows identifying the chemical nature of the surface recombination sites responsible for the low open-circuit potential of the devices.

In-free thin-film solar cells: Cu2ZnSn(S,Se)4 films generated from a single molecular precursor solution

255th National Meeting (2018)

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