Computational approach to explore suitable charge transport layers for all inorganic CsGeI3 perovskite solar cells

Organic-inorganic lead halides perovskite solar cells have undergone tremendous growth over the last decade and have achieved power conversion efficiency of 25.2%. However, lead toxicity has remained a key concern which is a major obstacle in their commercialisation. Cesium Germanium halide perovskites have proven to be an excellent alternative to lead perovskites as they exhibit higher optical absorbance and optical conductivity. In the present work, we have explored various charge transport layers (ETL and HTL) and their influence on the performance of CsGeI3 based PSCs using SCAPS-1D simulation software. It is found that when ZnOS and CuI are employed as ETL and HTL respectively in CsGeI3 based PSCs, the performance of the resultant PSC gets enhanced. Further, optimizations in terms of Perovskite layer thickness, defect density, thickness and electron affinity of ZnOS ETL has also been carried out. The effect of different metal electrodes, series and shunt resistances on the performance of the CsGeI3 based PSCs have also been studied. Finally, we have implemented all the optimum parameters in the proposed device structure (FTO/ZnOS/CsGeI3/CuI/Au) and observed a remarkable improvement in the performance parameters with VOC = 1.1432 V, JSC = 23.13 mAcm(-2), FF = 87.33% and PCE = 23.10%. This optimization of CsGeI3 based PSC would aid researchers in the experimental implementation of efficient lead-free all inorganic CsGeI3 based perovskite solar cells.