A bilateral cyano molecule serving as an effective additive enables high-efficiency and stable perovskite solar cells

The existence of defects in perovskite films is a major obstacle that prevents perovskite solar cells (PSCs) from high efficiency and long-term stability. A variety of additives have been introduced into perovskite films for reducing the number of defects. Lewis base-based additive engineering has been considered as an effective way to eliminate defects, especially the defects caused by the uncoordinated Pb²⁺. In this work, for the first time, a bilateral cyano molecule (succinonitrile, SN) which is a commonly used plasticizer in solid electrolyte of solid-state lithium batteries was selected as an additive to modify organic–inorganic hybrid perovskite films in PSCs. SN is featured with two cyano groups (–C≡N) distributing at both terminals of the carbon chain, providing two cross-linking points to interact with perovskites crystals via coordinating with uncoordinated Pb²⁺ and forming hydrogen bonds with –NH₂ groups in perovskite. It was found that the addition of SN into perovskite precursor solution could effectively reduce defects, particularly inhabit the appearance of Pb⁰ and thus suppress trap-assisted nonradiative charge carrier recombination. As a result, the efficiency of CH₃NH₃PbI₃(Cl) (MAPbI₃(Cl))-based PSCs was improved from 18.4% to 20.3% with enhanced long-term stability at N₂ and humid air atmosphere. This work provides a facile and effective strategy to enhance the PCE and stability of PSCs simultaneously, facilitating the commercialization of PSCs.