Hydroxyl substituted Spiro-OMeTAD as multi-site defect healing and carrier extraction enhanced surface passivator toward efficient perovskite solar cells

Ionic defects at surfaces and interfaces account for the trap-mediated nonradiative loss of perovskite solar cells (PSCs). Because these defects are composed of positively and negatively charged species, developing surface passivation materials with multi-site defect healing capacity is desirable. Herein, by replacing the side methoxy group (-OCH3) with a hydroxyl group (-OH), we report 2,20,7,70-Tetrakis [N,Ndi (4-hydroxyphenyl)amino]-9,90-spirobifluorene (Spiro-OHTAD) for PSCs applications. The -OH group of Spiro-OHTAD can bond with uncoordinated Pb2 thorn through a strong electrostatic interaction. Mobile Iand FA thorn defects can be stabilized by coordinative hydrogen bonding. In addition, the metallic Pb0 species, which correlate with the degradation of the PSCs, were largely eliminated after Spiro-OHTAD passivation. In addition to multi-defect healing, the introduced Spiro-OHTAD also improves the energy level mismatch at the perovskite/hole selective interface, facilitating the corresponding hole extraction process. Finally, our Spiro-OHTAD-passivated PSCs reached a device efficiency exceeding 20% and improved stability under ambient conditions. This study provides insights for improving the photocarrier crossinterface transportation of PSCs.