High-efficiency, lead-free FA0.8MA0.2SnI3 perovskite solar cell with passivated interfaces and tuned energy alignment: A wxAMPS simulation study

• This work presents a simulated lead-free n-i-p FA₀.₈MA₀.₂SnI₃ perovskite solar cell. • Device simulations yield a PCE of 21.53 % with a J SC of 27.12 mA/cm² and V OC of 1.06 V. • PCE is highly sensitive to bulk defect density in FA 0.8 MA 0.2 SnI 3 . • Efficiency drops from 21.53 % to 8.22 % with rising defect density due to V OC loss. • Acceptor-like defects limit efficiency; requires defect densities below 10 15 cm -3 . Lead toxicity hinders the commercialization of perovskite solar cells (PSCs). Tin-based perovskites offer an eco-friendly alternative, however Sn²⁺ oxidation causes high p-type doping and deep-level defects, leading to severe non-radiative recombination. This work presents a simulation study of a lead-free n-i-p PSC based on FA₀.₈MA₀.₂SnI₃, designed for high efficiency and stability. The optimized device uses SnO₂:PCBM as the electron transport layer, a PCBM interlayer doped with hypophosphorous acid (HPA) to suppress Sn²⁺ oxidation, and a V₂O₅:PEDOT:PSS hybrid hole transport layer for enhanced conductivity. A 2PACz self-assembled monolayer improves hole extraction. Material parameters and optical properties are calibrated to reflect realistic device physics. Simulation results show that the efficiency drops from 21.53 % to 8.22 % as the defect density increases from 1 × 10 14 to 5 × 10 17 cm⁻³, due to sharp reductions in V OC and FF; J SC remain stable, indicating robust charge generation. Mobility sweeps reveal that efficiency saturates when μ n ≥ 1 cm 2 /V·s (at fixed μ p = 10 ) and μ p ≥ 10 − 2 cm 2 /V·s (at fixed μ n = 10 ), highlighting the importance of balanced transport over extreme mobility. Spatial analysis of recombination reveals that the bulk perovskite layer dominates non-radiative losses, primarily due to acceptor-like defects from Sn²⁺ oxidation, while interface recombination at the ETL/perovskite and perovskite/HTL junctions plays a secondary role. This study provides a validated framework for high-efficiency, lead-free PSCs, emphasizing bulk defect passivation and transport balance as a viable pathway toward >21 % efficient scalable Sn-based solar cells for future tandem integration.