Oriented molecular bridge at the buried interface enables cesium-lead perovskite solar cells with 22.04% efficiency

Abstract

Meticulous engineering of the buried interface between the TiO₂ electron-transport layer and the CsPbI_3-xBr_x perovskite is crucial for interfacial charge transport and perovskite crystallization, thereby minimizing energy losses and achieving highly efficient and stable inorganic perovskite solar cells (PSCs). Herein, a functional molecular bridge is deliberately designed by integrating 3,4-thiophene dicarboxylic acid (TDDA) between the CsPbI_3-xBr_x perovskite and TiO₂ layer. It is demonstrated that the TDDA molecule exhibits a higher affinity towards the TiO₂ surface, forming tetradentate chelation through two C=O···Ti bonds and two C-O-H···O bonds. Subsequently, it establishes a connection with perovskite via thiophene S-Pb interaction, thus creating an oriented molecular bridge at the buried interface. This effectively enhances charge extraction, passivates bilateral interfacial defects, alleviates lattice strain, and improves perovskite crystallization. Consequently, the combination of these advantageous characteristics results in a power conversion efficiency (PCE) of 22.04% for a target CsPbI_3-xBr_x device with an active area of 0.09 cm². Importantly, when scaled up to larger-area devices with an active area of 1.0 cm², an remarkable PCE of 18.29% was achieved. Furthermore, the stabilities of both perovskite films and corresponding PSCs were significantly enhanced through this molecular bridge strategy.