Effect of low-cost hole transport layers (HTLs) on the performance parameters of lead-free homojunction CsGeI2Br-based perovskite solar cells

This work describes an extensive computational investigation of the effect of four low-cost materials, used as alternative HTLs, on the performance parameters of lead-free CsGeI 2 Br-based PSCs. The four HTL materials; CuO, Cu 2 O, P3HT and CuSbS 2 , were selected for their widespread availability, low cost and potentially better environmental stability. The effect of the various HTLs on the PSC energy band alignment and built-in potential was considered, followed by a detailed look at the effect of the CsGeI 2 Br absorber layer thickness, doping density, defect density in the absorber layer, back contact electrode, temperature, shunt and series resistance on the performance parameters of the PSCs for each of the HTLs. The investigation also looked at how the HTLs affect the electric field, generation-recombination rate, quantum efficiency, and I-V characteristic curves of the PSCs. The investigations were carried out with the aid of the Solar Cell Capacitance Simulator (SCAPS-1D). According to the results obtained, P3HT and Cu 2 O emerged as the better performing HTLs. In particular Cu 2 O, having the highest conduction band offset (CBO) and lowest valence band offset (VBO) for this CsGeI 2 Br-based PSC, worked out as the best HTL amongst the four. With this Cu 2 O HTL, the PSC exhibited the highest efficiency of 29.48 % when platinium (Pt) is used as a back contact electrode. Furthermore, a 3.85 % improvement in efficiency was obtained when comparing performance to existing CsGeI 2 Br-based PSC wherein Spiro-OMeTAD was used as HTL and gold as the back contact electrode.