Non‐Halogen Solvent Processed Binary Organic Solar Cells with Efficiency of 19% and Module Efficiency Over 15% Enabled by Asymmetric Alkyl Chain Engineering

Abstract The effective molecular design of non‐fullerene acceptors is important to high‐efficiency organic solar cells. Herein, asymmetric alkyl chain engineering is applied to design a new acceptor named DTC11. Compared with the model accpetor DTY6 with two long‐branched alkyl chains (2‐decyltetradecyl) on dithie‐nothiophen[3.2‐b]‐pyrrolobenzothiadiazole central unit, DTC11 owns a 2‐decyltetradecyl chain and an undecyl chain in the inner bay side of the central unit. It is found that with such modification of asymmetric long alkyl side chains, the crystallinity, absorption coefficient, and exciton lifetime of DTC11 are all improved. Moreover, in comparison with D18:DTY6 device, non‐halogen solvent processed D18:DTC11 device shows enhanced exciton generation and dissociation, improved charge transport as well as weak recombination, promoting higher short‐circuit current density and fill factor. Consequently, D18:DTC11 device delivers an outstanding efficiency of 19.0%. More significantly, non‐halogen solvent processed D18:DTC11 large‐area module (active area 21 cm 2 ) is fabricated by blade coating, and an impressive efficiency of 15.4% with fill factor of 74.6% is realized. This study demonstrates that the asymmetric alkyl chain engineering is a feasible strategy to design non‐fullerene acceptor with high‐performance and non‐halogen solvent processability, which are very essential for the commercialization of large‐area module.