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

The defects and strain of the buried SnO 2 /perovskite interface seriously affects the performances of n -i-p type perovskite solar cells. Herein, caesium closo-dodecaborate (B 12 H 12 Cs 2 ) is introduced into buried interface to improve the device performances. B 12 H 12 Cs 2 can passivate the bilateral defects of the buried interface, including the oxygen vacancy and uncoordinated Sn 2+ defects on SnO 2 side and the uncoordinated Pb 2+ defects on perovskite side. Three-dimensional aromatic B 12 H 12 Cs 2 can promote the interface charge transfer and extraction. [B 12 H 12 ] 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 B 12 H 12 Cs 2 due to the matched lattice between B 12 H 12 Cs 2 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 B 12 H 12 Cs 2 , the corresponding devices yield a champion power conversion efficiency of 22.10% with enhanced stability. The stability of devices by B 12 H 12 Cs 2 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.