Solution‐Grown Organic Single‐Crystalline Donor–Acceptor Heterojunctions for Photovoltaics

Organic single crystals are ideal candidates for high‐performance photovoltaics due to their high charge mobility and long exciton diffusion length; however, they have not been largely considered for photovoltaics due to the practical difficulty in making a heterojunction between donor and acceptor single crystals. Here, we demonstrate that extended single‐crystalline heterojunctions with a consistent donor‐top and acceptor‐bottom structure throughout the substrate can be simply obtained from a mixed solution of C 60 (acceptor) and 3,6‐bis(5‐(4‐ n ‐butylphenyl)thiophene‐2‐yl)‐2,5‐bis(2‐ethylhexyl)pyrrolo[3,4‐ c ]pyrrole‐1,4‐dione (donor). 46 photovoltaic devices were studied with the power conversion efficiency of (0.255±0.095) % under 1 sun, which is significantly higher than the previously reported value for a vapor‐grown organic single‐crystalline donor–acceptor heterojunction (0.007 %). As such, this work opens a practical avenue for the study of organic photovoltaics based on single crystals.