Dipolar Cation Chemically Bonded Tin Oxide and Bridged Buried Interface for Air-Processed Operationally Stable n-i-p Perovskite Solar Cells.

Abstract

The unstable electron transport layer (ETL) and buried interface, resulting from defects and weak adhesive strength, hampers the advancement of regular (n-i-p) perovskite solar cells (PSCs). Here, multisite dipolar molecules, namely 3,5-bis(trifluoromethyl)benzamidine hydrochloride (BTBACl), are employed to manipulate and stabilize SnO₂ ETL and buried interface for high-performance n-i-p PSCs. Due to its multiple active sites, BTBA⁺ can effectively chemically bonded SnO₂ nanoparticles and passivate various defects mainly including undercoordinated Pb²⁺/Sn⁴⁺ and I/O vacancies, thereby suppressing agglomeration of SnO₂ nanoparticles, homogenizing buried interface and reducing interface non-radiative recombination losses. Benefiting from the incorporation of two strong electron-withdrawing trifluoromethyl groups, the BTBA⁺ with large dipole moment enables efficient electron transfer and extraction at the buried interface. Ultimately, the BTBACl-modified n-i-p PSCs achieve a champion power conversion efficiency (PCE) of 26.20%, which is among the highest PCEs for air-processed PSCs. The significantly improved ETL and buried interface stabilities are translated into exceptional operational stability, maintaining 90.2% of its initial PCE after maximum power point tracking for 1000 h. This study offers a novel route to simultaneously stabilize ETL and buried interface from the perspective of functional group and dipole engineering, which promotes the development of n-i-p PSCs.