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. The 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 °C, 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 the 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 °C). These findings offer valuable insights into inhibiting phase transitions and optimizing crystallization processes in MA/Br-free FA-based PSCs.