Surface modification of ZnO electron transport layers with glycine for efficient inverted non-fullerene polymer solar cells

Interfacial engineering is crucial to improve the photovoltaic performance of polymer solar cells (PSCs). In this study, we demonstrate efficient inverted non-fullerene PSCs with ZnO modified by nontoxic glycine (Gly) as the electron transport layer (ETL). With the modification of Gly, work function of the ETL interlayer was decreased from 4.11 eV for ZnO to 4.02 eV for ZnO/Gly, which effectively increased the built-in electric field and hence improved the electron extraction. Furthermore, the surface energy of interlayer was also reduced from 69.1 mJ/m(2) for ZnO to 52.5 mJ/m(2), which is beneficial for the enrichment of the acceptor at the interface and hence facilities the electron transport and collection at cathode electrode. Therefore, the device based on PM6:IT-4F with ZnO/Gly as ETL exhibited a remarkably enhanced power conversion efficiency (PCE) of 14.0% relative to 12.9% for the control device with ZnO ETL, indicating a similar to 9% increase of the PCE with the simple molecular modification of the ETL. Meanwhile, this strategy can also be successfully applied to other non-fullerene and fullerene based inverted PSCs. Our work provides an effective approach to modify ZnO for high performance PSCs.