Application of a NADH-modified ZnO electron transport layer in high performance organic solar cells†

As an electron transport layer (ETL) widely used in organic solar cells (OSCs), ZnO has issues with energy level mismatch with the active layer and excessive surface defects, which ultimately reduce the efficiency of OSCs. Here, a ZnO:NADH ETL is prepared by modifying ZnO with green biomaterial nicotinamide adenine dinucleotide (NADH). XPS and UPS show that ZnO obtains electrons from NADH and decreases the work function of ZnO, thus lowering the interface barrier between ZnO and the active layer, which is conducive to electron collection in OSCs. At the same time, the oxygen vacancy density on the ZnO surface reduces after modification with biomaterial NADH, thus improving the electrical conductivity of ZnO. Finally, we use PM6:Y6 and PM6:L8-BO as active layers, and use ZnO:NADH as a novel ETL in OSCs, achieving efficiencies of 16.77% and 18.21%, respectively. The stability of the device with the ZnO:NADH ETL has also been improved to a certain extent. This study provides an effective method for ZnO modification, and also contributes to the environmental protection in the device preparation process.