ZnO:Bio-inspired polydopamine functionalized Ti3C2Tx composite electron transport layers for highly efficient polymer solar cells

• Bio-inspired ZnO:PDA-Ti 3 C 2 T x electron transport layer (ETL) is fabricated. • PDA-Ti 3 C 2 T x passivates the defects of ZnO by forming chelate interactions. • PDA-Ti 3 C 2 T x lowers the vacuum level of ETL by forming interface dipoles. • The device with new ETL presents high efficiency and excellent stability. The optimized electron transport layer (ETL) plays a crucial role in the practical application of polymer solar cells (PSCs). Herein, bio-inspired polydopamine (PDA) modified Ti 3 C 2 T x (PDA-Ti 3 C 2 T x ) as a multifunctional additive is dispersed into ZnO to fabricate ZnO:PDA-Ti 3 C 2 T x composite ETL. PDA-Ti 3 C 2 T x passivates the trap states of ZnO via forming strong and stable chelate interactions through Zn 2+ ions and PDA molecules. PDA-Ti 3 C 2 T x also lowers the vacuum level of transport layer by forming interface dipoles between catechol of PDA and Zn 2+ ions of zinc oxide. Moreover, PDA-Ti 3 C 2 T x constructs additional electron transport pathways by connecting the discontinuities among ZnO nanocrystals. As such, ZnO:PDA-Ti 3 C 2 T x composite ETL, with higher conductivity and proper work function, can effectively collect electrons in the PSCs. Compared with ZnO control devices, the performance of PSCs with ZnO:PDA-Ti 3 C 2 T x ETL is obviously enhanced with power conversion efficiencies (PCEs) from 10.34% to 12.07% based on PBDB-T:ITIC, 14.84–16.69% based on PM6:Y6, and 8.14–9.41% for PTB7:PC 71 BM, respectively. The ambient stability of the PSCs with ZnO:PDA-Ti 3 C 2 T x ETLs is significantly improved due to the increased hydrophobicity of ETL and the enhanced crystallinity of active layer. The novel ETLs provide a facile, eco-friendly, low-cost approach to realize the highly performance and stable PSCs.