Elucidating the Polymorph Morphology for Optimizing Aqueous Nanoparticle‐Based Organic Solar Cells

Despite the rapid progress of organic solar cells (OSCs) with an efficiency over 20% based on morphology optimization, the efficiency of aqueous/alcohol nanoparticle (np)‐based OSCs is still stuck at about 10% without synchronized growth using the same optimization approach. The efficiency gap is mainly due to the fact that conventional morphology optimization strategies for solution‐cast devices cannot be directly adopted for nanoparticle‐based devices. To illustrate, we first adopt one means of morphology optimizationdifferent molecular weight (Mn) of polymer to investigate mechanism of morphology modulation in nanoparticle films. The organic solution‐cast devices show similar performance based on different Mn of polymer, while aqueous np‐based devices occur large difference. The interaction of good/non solvent in nanosuspension synthesis process and long crystal growth period during np‐film formation process can magnify the aggregation behavior. The magnification behavior is also verified by additive optimization strategy. Strategies used for solution‐cast devices that pursue high regularity, tend to easily cause excessive phase separation in np‐based devices. Rational phase separation with small‐sized domain is more important than high ordering for np‐devices. The results help to understand the morphology modulation on np‐film and provide a sensible guide for future optimization in np‐OSCs.