Fabrication of ZnO interface layer from a novel aqueous sol-gel precursor solution for organic solar cells

To improve the morphology and charge transport property of zinc oxide (ZnO) interface layer in the field of organic solar cells (OSCs), a novel ZnO sol-gel precursor was developed by redox reaction among zinc powder (Zn), hydrogen peroxide (H2O2), and ammonia (NH3·H2O) in aqueous solvent. This aqueous ZnO sol-gel precursor has advantages in cost and stability. Furthermore, photoelectric conversion performance of OSCs with ZnO layer (aqueous) is better than that of device with ZnO layer (nonaqueous). To further elaborate the relevance between the ZnO interface layer and the device performance, optical and morphology characteristics of precursor solutions, ZnO layers, and active layers were studied. Meanwhile, electrical characteristics of the OSCs were also analyzed. The results show less anion and larger colloidal particle size in aqueous sol-gel solution, which making the ZnO interface layer have fewer defects and larger surface roughness than nonaqueous-phase prepared ZnO layer. Thus, free electron could transfer from the active layer to ZnO layer more easily, and charge recombination is reduced at the interface. Moreover, the electron mobility of OSCs is also enhanced by the aqueous-phase prepared ZnO layer. Therefore, short-circuit current and photoelectric conversion performance of device are promoted.