Rational Design of Lewis Base Electron Transport Materials for Improved Interface Property in Inverted Perovskite Solar Cells: A Theoretical Investigation.

Electron transport materials (ETMs) play a vital role in electron extraction and transport at the perovskite/ETM interface of inverted perovskite solar cells (PSCs) and are useful in power conversion efficiency (PCE), which is limited by interface carrier recombination. However, strategies for passivating undercoordinated Pb2+ at the perovskite/ETM interface employing ETMs remain a challenge. In this work, a variety of heteroatoms were used to strengthen the Lewis base property of new ETMs (asymmetrical perylene-diimide), aimed at deactivating non-bonded Pb2+ at the perovskite surface through Lewis acid-base coordination. Quantum chemical analysis revealed that novel ETMs have matched the energy level of perovskite, which enables electron extraction at the perovskite/ETM interface. The results also suggest that the large electron mobility (0.57~5.94 cm2 V-1 s-1) of designed ETMs shows excellent electron transporting ability. More importantly, reinforced interaction between new ETMs and Pb2+ was found, which is facilitating to passivation of the defects induced by unsaturated Pb2+ at the perovskite/ETM interface. Furthermore, it is found that MA (CH3NH3+), Pb, and IPb (iodine substituted on the Pb site) defects at the perovskite/ETM interface could be effectively deactivated by the new ETMs. This study provides a useful strategy to design ETMs for improving the interface property in PSCs.