Organic Semiconductors for Vacuum-Deposited Planar Heterojunction Solar Cells

Relative to widely used solution-processed bulk heterojunction organic solar cells (OSCs), planar heterojunction (PHJ) OSCs by vacuum-depositing active layers sequentially avoid tedious control of the blend film morphology, and it is easy to understand the physical process at the donor/acceptor interface. Here we summarize the developments of electron donor and acceptor materials for vacuum-deposited PHJ OSCs in the past decades and discuss the relationship between molecular structure and device performance. Finally, the challenges and prospects for the development of vacuum-deposited PHJ OSCs are also proposed. In addition to some basic requirements for high performance organic photovoltaic materials, such as broad and strong absorption, matched energy levels between donors and acceptors, and high charge carrier mobility, we suggest that extending the exciton diffusion length of organic photovoltaic materials should boost PHJ OSCs gradually become another option for organic photovoltaic application.