An Amorphous Mesophase Generated by Thermal Annealing for High-Performance Organic Photovoltaic Devices

Thermal annealing of a p‐i‐n organic photovoltaic device containing a crystalline benzoporphyrin donor and solvated crystals of a silylmethylfullerene acceptor increases the device performance at a temperature where partial desolvation of the acceptor produces an amorphous mesophase. This suggests that the mesophase improves the hierarchical ordering of the materials, that is, the morphology of the n‐layer and the interfacial contact and, hence, the carrier generation efficiency at the donor–acceptor interface.