Stability improvement of inverted organic solar cells with thin organic protective layer

Encapsulation is one of the methods to prevent organic devices from degradation. We design a facile, effective bilayer structure of ∼250 nm thick as protective layer for organic solar cells (OSCs). This bilayer structure is composed of a free-radical scavenging 3-Hydroxyflavone (3-HF) film underneath a hydrophobic polyvinylidene difluoride (PVDF) layer. Devices packaged with this 3-HF/PVDF bilayer show better storage stability and light-soaking stability than those with individual layer. As obtained, the power conversion efficiencies of packaged devices remain 96.1%, 86.5%, and 69.7% of their original values after two months storage in relative humidity environment of 20%, 50%, and 77% at room temperature, respectively. The result can be understood as the cooperative effect of water molecule repelling property of PVDF and oxygen elimination ability of 3-HF. The purposed idea can be generalized to other organic devices to extend their shelf life and serve as a design guideline for developing thin encapsulation materials for wearable technology with simple processing and good performance.