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

Graphical Ideal candidates for high-performance photovoltaics , organic single-crystalline heterojunctions are difficult to prepare. Now, extended single-crystalline heterojunctions with consistent donor-top and acceptor-bottom structure throughout the substrate can be obtained from a mixed solution of donor and acceptor through sequential crystallization. These heterojunctions exhibit a significant photovoltaic effect. 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.