Lawrence Berkeley National Laboratory

Herein, three small molecule (SM)‐acceptors (POIT‐IC, POIT‐IC2F, and POIT‐IC4F) are developed by combining the side‐chain engineering located on the sp 3 ‐hybridized carbon atoms of the fused‐ring core and the fluorination of end groups. From ITIC to POIT‐IC, POIT‐IC2F, and then to POIT‐IC4F, the SM‐acceptors show gradually broadened absorption spectra, increased maximum extinction coefficient, crystallinity, and electron mobilities due to the synergistic effects of side‐chain engineering and fluorination. Compared with nonfluorinated ITIC and POIT‐IC, as fluorination broadens the molecular spectra, POIT‐IC2F and POIT‐IC4F with alkoxyphenyl side chains show less decreased LUMO levels than IT‐IC2F and IT‐IC4F with alkylphenyl side chains, which are conducive to both higher V oc and J sc for organic solar cells (OSCs). Combined with polymer donor PM6, the POIT‐IC4F‐based OSCs achieve a device efficiency of up to 13.8% with a high V oc of 0.91 V and J sc of 20.9 mA cm −2 , which are significantly higher than that of the control OSCs based on ITIC (8.9%), POIT‐IC (10.1%), or IT‐IC4F (12.2%). An efficiency of 13.8% is one of the highest PCEs reported for the annealing‐free OSCs. Our results show that the synergistic effects of side‐chain engineering and fluorination on SM‐acceptor can simultaneously broaden spectral response and minimize voltage loss of OSCs and ultimately achieve high device efficiency.