Synergistic effects of caesium closo-dodecaborate on buried interface for efficient and stable perovskite solar cells

Abstract

The defects and strain of the buried SnO2/perovskite interface seriously affects the performances of n-i-p type perovskite solar cells. Herein, caesium closo-dodecaborate (B12H12Cs2) is introduced into buried interface to improve the device performances. B12H12Cs2 can passivate the bilateral defects of the buried interface, including the oxygen vacancy and uncoordinated Sn2+ defects on SnO2 side and the uncoordinated Pb2+ defects on perovskite side. Three-dimensional aromatic B12H12Cs2 can promote the interface charge transfer and extraction. [B12H12]2− can enhance the interface connection of buried interface by forming B-H---H-N dihydrogen bond and coordination bonds with metal ions. Meanwhile, the crystal properties of perovskite films can be improved and the buried tensile strain can be released by B12H12Cs2 due to the matched lattice between B12H12Cs2 and perovskite. In addition, Cs+ can diffuse into perovskite to reduce the hysteresis behavior by inhibiting the I− migration. Arising from the enhanced connection performances, passivated defects, improved perovskite crystallization, enhanced charge extraction, inhibited ions migration, released tensile strain at buried interface by B12H12Cs2, the corresponding devices yield a champion power conversion efficiency of 22.10% with enhanced stability. The stability of devices by B12H12Cs2 modification have been improved, and it can still maintain 72.5% of the original efficiency after 1440 h, while the control devices can only maintain 20% of the original efficiency after aging in air condition of 20–30% RH.