Aqueous solution-processed GeO2: an anode interfacial layer for high performance and air-stable organic solar cells.

A simple and cheap method for depositing solution-processed GeO2 (sGeO2) film is proposed utilizing the weak solubility of GeO2 in water. X-ray photoelectron spectroscopy analysis reveals that a pure GeO2 thin film can be formed by casting its aqueous solution. This method can avoid the difficulty of vacuum evaporation by its high melting point. The sGeO2 film has been used successfully as an anode interfacial layer in poly(3-hexylthiophene) (P3HT) and indene-C60 bisadduct (IC60BA)-based bulk heterojunction organic solar cells with improved power conversion efficiency and device stability compared with that using conventional poly (3,4-ethylenedioxythiophene):poly (styrenesulfonate) (PEDOT:PSS); the improvement of the power conversion efficiency and the device stability are estimated to be 9% and 50%, respectively. The calculations of optical intensity in a whole cell demonstrate that a thin layer of sGeO2 could function as an optical spacer in the based bulk heterojunction (BHJ) organic solar cells (OSCs) for enhancing the light harvesting in the active layer. Interfacial evaluation by impedance spectroscopy shows that the sGeO2-based cell exists less charge carrier recombination and lower contact resistance. More importantly, the sGeO2 film processing is very simple and environmentally friendly, which has potential applications in green and low-cost organic electronics in the future.