Quasi-ohmic electron extraction in perovskite solar cells through controlled burstein–moss shifts in rare-earth doped SnO2 ETLs

Perovskite solar cells (PSCs) have rapidly evolved into next-generation photovoltaic devices because of their fascinating power conversion efficiencies and low manufacturing costs. However, achieving peak performance requires precise engineering of the electron transport layer (ETL) to optimise charge extraction and suppress recombination. Doping rare-earth (RE) into SnO2 is one potential way to enhance ETL properties and has been extensively studied1. In this study, we utilize SCAPS-1D simulations to investigate the impact of rare-earth (RE) doping (La, Ce, and Eu) in SnO2 ETLs within a FAPbI3-based PSC architecture. While variations in thickness and donor density of the perovskite layer were examined, our results reveal that device performance is primarily governed by bandgap engineering induced by the Burstein–Moss effect. This doping-induced bandgap widening shifts the conduction band edge, facilitating a quasi-ohmic contact and superior band alignment with the FAPbI3 absorber. At high defect densities and thicker absorber layer, however, a performance crossover was observed, highlighting the sensitivity of optimized interfaces to severe Fermi-level pinning. Motivated by this findings, we systematically optimized the perovskite absorber thickness and defect density (Nt), identifying a critical sweet spot at 0.6 μm and 1014 cm-3, respectively, where photon harvesting and bulk recombination are balanced. Notably, La-doped SnO2 exhibited the highest tolerance to bulk defects, maintaining superior Voc and FF through enhanced extraction kinetics that outrun trap-assisted recombination. Under optimized conditions, the La-doped device emerged as the champion configuration, significantly outperforming pristine device and marginally better than Ce-, and Eu-doped variants. These findings provide a fundamental framework for leveraging RE-doping to engineer interfacial energy levels, offering a clear pathway for the development of high-efficiency, defect-tolerant perovskite photovoltaics.