Solution-Processable Fluorinated Hydrophobic Cathode Interlayers for High-Stability Conventional Organic Solar Cells

Hydrophobic cathode interlayers (CIL) can prevent water molecules into active layer, resulting in an enhanced long-term stability for organic solar cells (OSCs). However, the intrinsic liposolubility limits the application of hydrophobic CIL in conventional OSC devices. Herein, we report a series of novel hydrophobic water/alcohol-soluble conjugated polymers (H-WSCPs) (PFN-F50, PFN-F25, and PFN-F12.5) through simple side chain engineering. H-WSCPs combining alcohol solubility and hydrophobicity have potential application for improvement in the stability of conventional OSC devices. The solubility in alcohol solvents avoids erosion of the active layer during the processing. These fluorinated H-WSCPs present almost unchanged photoelectric characteristics compared with PFN-Br, achieving a comparable power conversion efficiency with that of PFN-Br-based OSCs in conventional devices. More importantly, through the introduction of the fluorinated alkyl chain, these polymers obtain excellent hydrophobicity, resulting in an increased water-resistance capability. CIL adopting fluorinated H-WSCPs can effectively prevent moisture from destroying the active layer, leading to an extended lifetime for OSC devices. After illumination for 600 h, the PFN-F25 conventional device maintained 75% of the initial value. This work provides a simple method to design hydrophobic CIL for conventional OSCs with high stability.