A mechanically and thermally stable and electron-selective ZnO/CH3NH3PbI3 interface is created via hybridization of a polar insulating polymer, poly(ethylene glycol) (PEG), into ZnO nanoparticles (NPs). PEG successfully passivates the oxygen defects on ZnO and prevents direct contact between CH3NH3PbI3 and defects on ZnO. A uniform CH3NH3PbI3 film is formed on a soft ZnO:PEG layer after dispersion of the residual stress from the volume expansion during CH3NH3PbI3 conversion. PEG also increases the work of adhesion of the CH3NH3PbI3 film on the ZnO:PEG layer and holds the CH3NH3PbI3 film with hydrogen bonding. Furthermore, PEG tailors the interfacial electronic structure of ZnO, reducing the electron affinity of ZnO. As a result, a selective electron-collection cathode is formed with a reduced electron affinity and a deep-lying valence band of ZnO, which significantly enhances the carrier lifetime (473 μs) and photovoltaic performance (15.5%). The mechanically and electrically durable ZnO:PEG/CH3NH3PbI3 interface maintains the sustainable performance of the solar cells over 1 year. A soft and durable cathodic interface via PEG hybridization in a ZnO layer is an effective strategy toward flexible electronics and commercialization of the perovskite solar cells.
Keywords: ZnO:PEG blend; adhesive interface; durable interface; electron-selective interface; perovskite solar cells.