In organic solar cell (OPV) devices, the most important part is the organic active layer. The active layer is mainly composed of two parts: one part is the conjugated polymer or small molecule of electron donor, and the other part is fullerene or non-fullerene derivative of electron acceptor. Different donors and acceptors are selected for the active layer, so that the open-circuit voltage, short-circuit current and energy conversion efficiency of the OPV device can be regulated. In the active layer, the donor units mainly include thiophenes, benzothiophenes, polyphenylenes, and cyclopentadithiophenes. The performance modification of donor materials can be regulated by optimizing the main chain structure, optimizing side chain groups, introducing π groups, and introducing heteroatoms. The optimization and selection of donor materials can significantly improve the photoelectric conversion efficiency of OPV devices, reduce costs, and enhance the potential of flexible devices, thereby expanding the application field of OPV.
Figure 1. OPV device active layer structure
- Polymer OPV device: The polymer OPV donor material with high photoelectric conversion efficiency should have the following properties: (1) Broad and strong absorption in the solar range; (2) The energy level should match the acceptor material; ( 3) The hole mobility should be high; (4) It has better solubility, film formation and stability. Common polymers are polystyrene, polythiophene, and benzodithiophene. These polymers all have good planar structures, which greatly enhance the delocalization ability of electrons and the intermolecular π-π interactions. In addition, the conjugated polymer has a higher effective conjugation length, and its absorption spectrum has a significant red shift, and its mobility is also significantly improved. The good properties of polymer donor materials make OPV devices more widely used.
- Small-molecule OPV devices: Small-molecule donor materials have various modifiable types and a good degree of donor-acceptor blending, which makes small-molecule OPV devices have broad application prospects. Small molecule donor materials have many modifiable sites on the structure, and various types of structural optimizations can be performed on them. Moreover, the small molecule donor materials are easy to synthesize, purify and separate. Therefore, small-molecule OPV devices are simple to prepare and have strong performance controllability, which can reduce the cost of batteries, simplify the process flow, and enhance the development potential of batteries.
- Huiting Fu, Zhaohui Wang, Yanming Sun. Polymer Donors for High-Performance Non-Fullerene Organic Solar Cells [J]. Angew. Chem. Int. Ed., 2018, 58, 4442-4453.