Solvent vapor annealing effect on organic solar cells based on a nonfullerene acceptor

A nonfullerene acceptor, FBTT‐BORH, was synthesized based on a central core consisting of a monofluorinated benzothiadiazole unit flanked by thiophene groups with rhodanine (RH) end groups functionalized with octyl chains for use as an electron acceptor in organic solar cells (OSCs). The UV–vis absorption spectra showed that solvent vapor annealing (SVA) effectively enhanced the molecular aggregation of FBTT‐BORH compared with that of the as‐cast film. This improvement led to higher short‐circuit current densities and fill factors in OSCs fabricated using PTB7‐Th as the polymer donor and FBTT‐BORH as the acceptor. The SVA‐treated FBTT‐BORH‐based device achieved a power conversion efficiency of 6.73% and an open‐circuit voltage close to 1.0 V. To further understand the efficiency enhancement induced by SVA, the charge recombination behavior, hole and electron mobilities, and film morphologies were examined. AFM, TEM, GIWAXS, and UV–vis analyses revealed suppressed recombination, higher charge mobility, improved molecular ordering, and enhanced crystallinity relative to the as‐cast condition, providing direct evidence that SVA treatment effectively regulates molecular arrangement and promotes superior device performance.