Block Copolymer as a Nanostructuring Agent for High‐Efficiency and Annealing‐Free Bulk Heterojunction Organic Solar Cells

The active layer nanostructure in bulk heterojunction organic solar cells plays a key role on the properties of charge transfer, transport, and consequently on the PCE. Ideally a cocontinuous network of donor–acceptor domains with a length scale comparable to the exciton diffusion length is required. [ 4 ] To obtain an optimized nanostructured active layer, an annealing process (thermal and/or solvent) is commonly performed, leading to an increase in photovoltaic performance. As an example, for the classical poly(3-hexylthiophene) (P3HT):phenyl-C 61 -butyric acid methyl ester (PCBM) blend, the PCE rises from around 1% to 5% after annealing (the average value being 3%). [ 5–7 ]