Flexible side-chain optimization in polymer donor enables improved photovoltaic performance

In this work, we apply a flexible side-chains engineering strategy to manipulate the physicochemical properties of the naphtho [2,3-c] thiophene-4,9-dione (NTDO)-based polymer donors. By replacing 2-ethylhexyl chain on the NTDO unit of PBN-S with 2-butyloctyl chains, the resulting polymer PBN-SBO possesses better solubility in commonly used organic solvents, weaker crystallinity, and better miscibility with acceptor material Y6. It is observed that the PBN-SBO:Y6 blend formed better morphology than the PBN-S:Y6 blend film, enabling improved charge carrier transport and less charge recombination. As a result, the PBN-SBO:Y6-based polymer solar cell (PSC) achieved a significantly improved power-conversion efficiency (PCE) of 16.22% as compared to the PBN-S:Y6-based device with a PCE of 12.86%. This work demonstrates the critical effect of side-chain engineering in manipulating the physicochemical properties towards improved photovoltaic performance and the great potential of NTDO unit in designing high-performance polymer donor materials for PSCs.