Ion migration inhibition and defect passivation via sulfonate salt coordination for high-performance perovskite solar cells with enhanced phase stability

Abstract

Perovskite solar cells (PSCs) have achieved remarkable advancements in power conversion efficiency (PCE). However, they still face challenges such as hysteresis and degradation, primarily caused by ion migration, which results in reduced carrier mobility and degradation of perovskite devices. To address these issues, a solution is proposed by introducing sulfonate salt 6-bromo-2-naphthyl triflate (BNT) into the perovskite. BNT can act as an inhibitor of ion migration and enhances the perovskite phase stability. Experimental results indicate that the Br⁻ ions in BNT effectively passivate vacancy defects by occupying the iodine vacancy sites, thus inhibiting ion migration caused by them. This leads to an increase in the activation energy of ion migration from 0.52 eV to 0.87 eV calculated by the Arrhenius relation. Additionally, the SO groups in BNT can bond with uncoordinated Pb²⁺ defects, thereby passivating cationic defects. The synergistic passivation effect of Br⁻ and SO groups also significantly reduces the trap-state density and improves the crystal quality of the perovskite film. As a result, a champion PCE of 21.95% is achieved, while the hysteresis is reduced from 7.3% to 2.8%. Moreover, the perovskite film subjected to 648 hours of aging under ambient conditions with 45% relative humidity demonstrates minimal decomposition and phase transition. The device retains 83% of its initial PCE, whereas the control one can only maintain 29%.