High Electron Affinity Enables Fast Hole Extraction for Efficient Flexible Inverted Perovskite Solar Cells

Inverted perovskite solar cells (PSCs) with low-temperature processed hole transporting materials (HTMs) suffer from poor performance due to the inferior hole-extraction capability at the HTM/perovskite interfaces. Here, molecules with controlled electron affinity enable a HTM with conductivity improved by more than ten times and a decreased energy gap between the Fermi level and the valence band from 0.60 to 0.24 eV, leading to the enhancement of hole-extraction capacity by five times. As a result, the 3,6-difluoro-2,5,7,7,8,8-hexacyanoquinodimethane molecules are used for the first time enhancing open-circuit voltage (V-oc) and fill factor (FF) of the PSCs, which enable rigid-and flexible-based inverted perovskite devices achieving highest power conversion efficiencies of 22.13% and 20.01%, respectively. This new method significantly enhances the V-oc and FF of the PSCs, which can be widely combined with HTMs based on not only NiOx but also PTAA, PEDOTT:PSS, and CuSCN, providing a new way of realizing efficient inverted PSCs.