Improved Domain Size and Purity Enables Efficient All‐Small‐Molecule Ternary Solar Cells

An all-small-molecule ternary solar cell is achieved with a power conversion efficiency of 10.48% by incorporating phenyl-C71 -butyric-acid-methyl ester (PC71 BM) into a nonfullerene binary system. The addition of PC71 BM is found to modulate the film morphology by improving the domain purity and decreasing the domain size. This modulation facilitates charge generation and suppresses charge recombination, as manifested by the significantly enhanced short-circuit current density and fill factor. The results correlate the domain characteristics with the device performance and offer new insight from the perspective of morphology modulation for constructing efficient ternary devices.