Science News: 2022 Adv. Funct. Mater., How to Improve the Underwater Stability of Organic Photovoltaic Cells? Using Water-Insensitive Electron Transport and Photoactive Layers

　　Organic Photovoltaic (OPV) is the third generation of photovoltaic technology. Due to its advantages of easy manufacture, low cost, and good processing performance, it has received a lot of attention in recent years and has been applied in many fields. Adv. Funct. Mater. published a study in 2022, and the degradation of device performance in OPV due to water ingress is one of the obstacles to its commercialization. Here, the research team used a combination of a nanoparticle titanium dioxide (np-TiO₂) electron transport layer (ETL) and an all-polymer bulk heterojunction (BHJ) photoactive layer to endow OPV with better water resistance and better performance than the commonly employed zinc oxide (ZnO) ETL or polymer:small molecule BHJ blends. Therefore, polymeric donors/acceptors are first shown to have better water-immersion than their small-molecule counterparts.

　　Among the studied BHJ systems, the all-polymer blend shows the lowest loss of absorbance losses after water immersion. In addition, it is found that:

1. Adjusting the structure of TiO₂ ETL from planar to nanoparticles can effectively enhance the adhesion at the ETL/BHJ interface to prevent physical delamination.
2. The np-TiO₂/all-polymer blend (half-cell) is demonstrated to exhibit excellent stability under water immersion, i.e., the morphology and charge carrier transfer are unchanged, and the efficiency of the complete cells are unchanged.

　　This study demonstrates the great potential of all-polymer blends and np-TiO₂ ETL to improve the durability of unencapsulated OPVs under high humidity environments and even water immersion.