Polyimide/ZnO composite cooperatively crosslinked by Zn²⁺ Salt-Bondings and hydrogen bondings for ultraflexible organic solar cells

High power conversion efficiency (PCE), operational stability and low cost are essential for the commercial application of ultraflexible organic solar cells (OSCs), but it is still challenging to realize these purposes simul-taneously. Here, a high-performance polyimide (PI)/ZnO composite (PI-ZnO) was prepared via introducing ZnO nanocrystals to an elaborately designed PI with both hydrogen bondings and abundant carboxyl groups (PI-COOH), where the fabrication cost of the PI-COOH was reduced by using common solvent under air atmosphere. With the UV absorption of ZnO nanocrystals, Zn2+ salt-bondings (formed via carboxyl ligand exchanges) and strong hydrogen bondings integrated in the single material, the PI-ZnO showed outstanding solvent-resistant, mechanical, thermal, and UV filtering properties. An untraflexible OSC with an optimal PCE of 13.55 % (average of 13.42 %) was constructed based on the AgNWs semi-embedded ultrathin flexible transparent com-posite electrode (FTCE, -6 mu m). The ultraflexible OSC showed outstanding mechanical stability (PCE decreased by less than 5 % after 4000 bending cycles at a small bending radius of 1 mm) and superior UV light stability (PCE decreased by only-3 % after UV light irradiation for 6 h). This work would provide a new approach for fabricating high-performance, stable and low-cost ultraflexible OSCs.