Performance analysis and optimization of inverted inorganic CsGeI3 perovskite cells with carbon/copper charge transport materials using SCAPS-1D

Organic-inorganic perovskite solar cells (PSCs) have achieved the power conversion efficiencies (PCEs) of more than 25%. However, the organic compound in the material is causing structural degradation of the PSC owing to heat (thermal instability), humidity and moisture. This has led to the exploration of only inorganic perovskite materials. Inorganic PSCs such as caesium have seen a breakthrough by achieving highly stable PSC with PCE exceeding 15%. In this work, the inorganic non-toxic PSC of caesium germanium tri-iodide (CsGeI3) is numerically modelled in SCAPS-1D with two carbon-based electron transport layers (ETLs) and two copper-based hole transport layers (HTLs). This study introduces in-depth numerical modelling and analysis of CsGeI3 through continuity and Poisson equations. Cu HTLs are selected to increase the electric conductivity of the cell, while carbon-based ETL is used to increase the thermal conductivity of the PSC. A total of four unique PSC structures are designed and presented. A systematic approach is adopted to obtain the optimized PSC design parameters for maximum performance. From the optimized results, it is observed that the C-60/CsGeI3/CuSCN structure is the highest performance PSC, with open-circuit voltage (V-oc) of 1.0169 V, short-circuit current density (J(sc)) of 19.653 mA cm(-2), fill factor of 88.13% and the PCE of 17.61%. Moreover, the effect of quantum efficiency, electric field, interface recombination, interface defects, layer thickness, defect density, doping concentration, working temperature and reflection coating on the cell performance are studied in detail.