High-performance organic solar cells based on polymer donor/small molecule donor/nonfullerene acceptor ternary blends

We used mid-bandgap small molecule donor TR as a third component to fabricate ternary nonfullerene organic solar cells (OSCs) based on narrow-bandgap polymer donor PTB7-Th and narrow-bandgap nonfullerene acceptor FOIC. TR exhibits full miscibility with PTB7-Th and efficient energy transfer to PTB7-Th, enhances stacking of PTB7-Th, hole mobility and charge generation of the blends, and ultimately improves device performance. Compared with the binary PTB7-Th/FOIC blend, the ternary device with 25% TR (w/w) yields simultaneously improved open-circuit voltage, short-circuit current density and fill factor. Finally, single-junction OSCs based on the ternary PTB7-Th/TR/FOIC blend yield power conversion efficiency as high as 13.1%, higher than the binary OSCs (12.1%). The ternary device efficiency exhibits high tolerance to thickness variation (>12% in the range of 80-200 nm). Transient absorption spectroscopy confirms the importance of long-range resonant energy transfer from donor to acceptor phases.