Synergy Effect of a π‐Conjugated Ionic Compound: Dual Interfacial Energy Level Regulation and Passivation to Promote Voc and Stability of Planar Perovskite Solar Cells

Defects and energy offsets at the bulk and heterojunction interfaces of perovskite are detrimental to the efficiency and stability of perovskite solar cells (PSCs). Herein, we designed an amphiphilic π‐conjugated ionic compound (QAPyBF4), implementing simultaneous defects passivation and interface energy level alignments. The p‐type conjugated cations passivated the surface trap states and optimized energy alignment at the perovskite/hole transport layer. The highly electronegative [BF4]− enriched at the SnO2 interface featured desired band alignment due to the dipole moment of this interlayer. The planar n‐i‐p PSC had an efficiency of 23.1 % with Voc of 1.2 V. Notably, the synergy effect elevated the intrinsic endothermic decomposition temperature of the perovskite. The modified devices showed excellent long‐term thermal (85 °C) and operational stability at the maximum power point for 1000 h at 45 °C under continuous one‐sun illumination with no appreciable efficiency loss. A π‐conjugated ionic multifunctional additive (QAPyBF4) was developed and introduced into perovskite solar cells (PSCs). QAPyBF4 passivated defect states in the perovskite layer, adjusted energy level alignment at the perovskite/ETL and perovskite/HTL interfaces, and prevented the decomposition of perovskite crystals. Therefore, a planar PSC with QAPyBF4 delivered an efficiency of 23.1 % with a remarkable Voc of 1.2 V and operational stability.