20.730% highly efficient lead-free CsSnI₃-based perovskite solar cells with various charge transport materials: a SCAPS-1D study

Perovskite solar cells (PSCs) are gaining increasing importance in the field of photovoltaics due to their long diffusion length, extended coefficient of absorption, improved mobility of carriers, low exciton binding energy, adjustable band gap, and good tolerance. However, the presence of toxic lead has caused a concern due to its negative impact on humans and the environment. This has led to an interest in lead-free alternatives. Despite researchers' interest, commercial feasibility has been difficult due to lack of numerical studies to optimize parameters before experimentation. This research presents a study on lead-free CsSnI₃ PSCs using one-dimensional solar capacitance simulation (SCAPS-1D) tool. The initial device consists of TiO₂ as the electron transport layer (ETL) and Spiro-OMeTAD as the hole transport layer (HTL). When the device was calibrated, the results were 13.631% for PCE, 82.459% for FF, 18.637 mA/cm² for J_sc, and 0.887 V for V_oc. Various HTLs and ETLs were used to determine FTO/WS₂/CsSnI₃/PEDOT:PSS/Au as the most effective optimized solar cell structure. After optimizing the PSC parameters including; the thickness of the ETL, the doping concentration of the ETL, defect density of absorber, ETL/absorber defect density, absorber/HTL defect density, and the metal back contact, the device yielded an optimized PCE of 20.730%, which is 1.52 times higher than the PCE for the unoptimized device. Other parameters for the optimized device are; FF = 80.340%, J_sc = 25.315 mA/cm² and V_oc = 1.019 V. The influence of temperature, shunt, and series resistances on the metric performance of the optimized cell were systematically analyzed. The quantum efficiency, recombination, and generation rate were used to further validate our results.