Harnessing the potential of lead-free Sn–Ge based perovskite solar cells by unlocking the recombination channels

Abstract

Perovskite solar cells (PSCs) have celebrated a decade of investigation as a promising photovoltaic technology. However, they contain lead, so inorganic lead-free PSCs can be designed as green and clean energy sources. To overcome the current obstacles in lead-free PSCs, the stability and performance gap should be minimized. The drift-diffusion simulation model is a conducive way to understand the working mechanism in a thin-film solar cell. Here we adopted a computational approach to design and investigate the performance of CsSn_0.5Ge_0.5I₃ as a light harvester. We optimize the thickness of the perovskite, for its use in an inverted planar structure (FTO/PCBM/CsSn_0.5Ge_0.5I₃/Spiro-OMeTAD/Au). Furthermore, cerium oxide (CeO_x) and PTAA are used as alternative electron and hole transport layers, respectively. We studied the effect of trap density in the bulk CsSn_0.5Ge_0.5I₃ and its impact on performance, recombination rate, and diffusion length. The open-circuit voltage (V_oc) showed a significant improvement and the correlation with the trap density at the interface layers is established. We noted that the defect density at the perovskite/hole selective layer interface has a profound impact on the performance of lead-free PSCs as compared to the electron selective layer/perovskite interface. After optimizing defect parameters, the lead-free PSC can deliver a PCE of 24.20%, with V_oc = 1170 mV, J_sc = 25.80 mA cm⁻², and FF = 80.33%. Our findings provide access guidelines and pave the way for lead-free PSCs based on the Sn–Ge combination to approach their limit.