Ionic compensation for defect reduction and enhanced performance of tin-based perovskite solar cells

The development of tin-based perovskite solar cells (Sn–PSCs) is hindered by the issue of high defect density in Sn-perovskite film, which seriously deteriorates the power conversion efficiency (PCE) and stability. Herein, an ionic compensation strategy is proposed by adding guanidine iodide (GAI) into the FA0.75MA0.25SnI3 precursor solution to fabricate high-quality Sn-perovskite films by healing multi-vacancy defects. GA+ cations are rationally incorporated into perovskite crystal to compensate for the organic cation vacancies during thermal annealing, while the I-rich condition can simultaneously heal the iodine vacancies. This method significantly improves the crystalline quality and surface morphology of Sn-perovskite films during annealing. At the same time, the optimized film obtains a reduction in the density of defect states and an extension of the carrier lifetime. Consequently, the best performing Sn-PSC modified by ionic compensation with GAI achieves an increase in PCE from 7.56% (control device) to 10.41%, while also improving stability, retaining ∼83% of the initial PCE after aging for 30 days in an N2 environment without encapsulation. This work represents that the ionic compensation strategy is an effective and practical approach toward reducing defects and realizing enhanced performance of Sn–PSCs.