Tuning the Crystallinity and Phase Separation by Two‐Step Annealing Enables Block Copolymer‐Based Organic Solar Cells with 15% Efficiency.

Block copolymer‐based organic solar cells (OSCs) possess better stability than their binary all‐polymer counterparts; thus, promoting the power conversion efficiency (PCE) of them to a higher level would be meaningful to achieving a higher level of efficiency–stability balance. Herein, two‐step annealing combining solvent vapor and thermal annealing (TA) upon cast films is deployed and 15% efficiency for block copolymer PM6‐b‐PY‐IT‐based OSCs is realized, which appeals to the level of traditional binary all‐polymer solar cells. The morphology optimization of the properly enhanced crystallite size, global crystallinity, and reduced pure phase length scale and maintained phase purity are supposed to be the driving force of increase device performance. This work offers a high PCE for the typical type of solar cell, brightening the prospect of realizing OSCs' application. [ABSTRACT FROM AUTHOR]