Mussel-inspired surface engineering for highly efficient and stable flexible non-fullerene organic solar cells

The inverted organic solar cells (OSCs) are generally considered to have better stability. However, the commonly used ZnO electron transport layer (ETL) requires high-temperature annealing, contains surface defects , exhibits photocatalytic activity , and is inherently brittle, limiting its suitability for efficient and stable flexible devices. Herein, a mussel-inspired surface engineering is utilized to develop a novel ZnO:PDA ETL. Dopamine (DA) is introduced into the ZnO precursor and undergoes spontaneous oxidation and polymerization to form a PDA network embedded within the ZnO lattice. The catechol and amino groups in PDA passivate defects and lower the work function (W f ) of the film. The obtained ZnO:PDA film is smoother and more hydrophobic, thereby improving active layer deposition and interfacial contact. As a result, inverted OSCs with ZnO:PDA achieve superior power conversion efficiencies (PCEs) of 16.59 % and 17.85 % in PM6:Y6 and PM6:L8-BO-based devices, respectively, outperforming pure ZnO-based devices (PCE = 15.61 %/17.13 %). More importantly, the integration of the PDA network also enhances both mechanical flexibility and robustness, leading to the flexible OSCs with a higher PCE of 16.47 % and improved flexural endurance. This work offers a simple yet effective strategy for modifying ZnO to achieve efficient and stable flexible OSCs. A mussel-inspired strategy is used to develop a novel ZnO:PDA electron transport layer (ETL). In situ oxidation and polymerization of dopamine (DA) within the ZnO lattice form a polydopamine (PDA) network, enhancing the optoelectronic properties of the ETL for highly efficient and stable flexible non-fullerene OSCs.