Efficient and Stable Inverted MA/Br-Free 2D/3D Perovskite Solar Cells Enabled by α-to-δ Phase Transition Inhibition and Crystallization Modulation

Abstract

The α-to-δ phase transition and lattice defects pose significant challenges to the long-term stability of methylammonium (MA)/bromide (Br)-free formamidinium (FA)-based perovskite solar cells (PSCs). Here we propose an approach for bulk incorporating benzyl carbamimidothioate hydrochloride (BLSCl) to create 2D/3D perovskites without using MACl additive. This method effectively inhibits the α-to-δ phase transition and allows for improved modulation of crystallization within MA/Br-free FA-based PSCs. BLS-induced multi-quantum-well structure significantly prevents water and oxygen corrosion. Moreover, BLS forms multiple hydrogen bonds and S-Pb coordination bonds with perovskite inorganic layers for modulating crystallization and passivating defects to create high-quality 2D/3D perovskite films. Consequently, the improved 2D/3D FA-based perovskite film possesses outstanding stability under harsh conditions (T = 200 ℃, RH = 80%) without α-to-δ phase transition. The resultant PSCs achieved a remarkable efficiency of 25.96% (0.1 cm2). More importantly, an outstanding PCE of 24.54% (certified 23.94%) was attained for 1.01 cm2 device, which is the highest value for inverted MA/Br-free FA-based PSCs without MACl additive. Additionally, the optimized device demonstrates exceptional operational stability, with a T96 value exceeding 1200 hours (T = 60 ℃). These findings offer valuable insights into inhibiting phase transitions and optimizing crystallization processes in MA/Br-free FA-based PSCs.