33.8% Efficient FAPbI ₃ /Si Monolithic Tandem Solar Cell with 2D CPAH Perovskite Passivation Layer

Abstract The power conversion efficiency (PCE) of standalone FAPbI 3 ‐based solar cells has shown a continuous increase since its inception, reaching a record PCE of ≈26%. Recombination losses, including radiative, Shockley‐Read‐Hall, and thermodynamic limits the open‐circuit voltage of standalone solar cells, thereby hindering performance. Proper surface passivation utilizing 2D perovskite materials, in conjunction with appropriate electron and hole transport layers, metal‐semiconductor contacts, and reduced defect density in absorber layer, may address these challenges. This study presents the proposal and simulation of a control device lacking a passivation layer, specifically FTO/TiO 2 /FAPbI 3 /PEDOT:PSS, alongside a target device featuring a 2D passivation layer of cyclopropylcarbamidine hydrochloride (CPAH), denoted as FTO/TiO 2 /FAPbI 3 /2D‐CPAH/PEDOT:PSS, and a two‐terminal (2T) monolithic tandem solar cell (TSC) configured as FTO/TiO 2 /FAPbI 3 /2D‐CPAH/PEDOT:PSS/IZO/n‐nc‐SiO x /i‐a‐Si:H/n‐c‐Si/i‐a‐Si:H/p‐nc‐Si:H. The illuminated current‐voltage characteristics, external quantum efficiency, integrated current density, and Suns‐V OC are analyzed to evaluate the performance of both proposed solar cells. An optimized control device yields a V OC of 1147.0 mV, whereas the device with a passivation layer achieves a V OC of 1240.3 mV, ≈98.5% of its SQ limits. The optimally designed target cell achieves a substantial PCE of 29.06%. Additionally, a notable PCE of 33.78% for the 2T TSC using the target device as the top subcell has been achieved.