Revealing the structural effects of non-fullerene acceptors on the performances of ternary organic photovoltaics under indoor light conditions

Strong absorption and tunable energy levels of non-fullerene small molecules offer enormous potential for organic photovoltaics (OPVs) to harvest energy from various light sources. However, the selection of suitable materials with an effective optical, electrical, and compatible morphological properties remains a big challenge. In this work, we demonstrated the effect of employing different non-fullerene acceptors (NFAs) as a crystalline modulator in efficient ternary-blend OPVs for indoor applications. Two different types of NFAs with different chemical structures and crystallinity, i.e. amorphous (PDI2 and PDI4) and semi-crystalline (IDT and IDDT), were introduced as the third component into a host OD:PC₇₁BM binary-blend system. The optimized ternary-blends exhibited the power conversion efficiencies of 20.54% (OD:PC₇₁BM:PDI2), 18.27% (OD:PC₇₁BM:PDI4), 21.13% (OD:PC₇₁BM:IDT), and 19.05% (OD:PC₇₁BM:IDDT), respectively, under indoor light source (1000 lux, LED lamp) thereby completely outperforming the host binary-blend (14.15%). The variation of the OPV performance was investigated and correlated with the photophysical and morphological properties of the corresponding NFAs. Particularly, the addition of semi-crystalline IDT among other NFAs enabled the formation of compact nanoscale morphology with well-dispersion and smaller π-π stacking distance, thereby resulting in the efficient charge separation, the faster charge carrier transport, the reduced energetic disorder, and the suppression of non-geminate recombination. Overall, this study indicated that the addition of the third component with appropriate morphological properties can effectively improve the OPV performance under indoor light conditions.