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

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.