As a clean energy, solar energy has two advantages of no pollution to the environment and a wide range of sources. A solar cell is a device that directly converts light energy into electrical energy through the photoelectric effect or photochemical effect. The conversion active layers used in organic solar cells (OPV) are organic compounds with a wide range of sources and highly tunable properties. According to the molecular weight of organic matter, OPV can be divided into polymer solar cells and small molecule solar cells. In OPV, the energy conversion efficiency of solar cells with a bulk heterojunction structure for the active layer is extremely high. This active layer is mainly prepared from acceptor material and donor material. The acceptor material refers to a material that can accept electrons. Acceptor materials with excellent performance generally have the following conditions: (1) strong and wide absorption in the visible light region; (2) longer exciton diffusion length, so that excitons can efficiently migrate to the donor-acceptor interface; (3) higher LUMO energy level; (4) higher electron mobility; (5) good charge transfer ability. The structurally rich acceptor materials endow OPV devices with excellent properties and expand the application fields of OPV devices.
Figure 1. Chemical structures of some acceptor materials
- Organic solar cells(OPV): OPV using small organic molecules or polymers as active materials have the advantages of being able to be fabricated into flexible and portable devices, low in production cost, and have broad application prospects. In OPV, organic semiconductor materials with photosensitive properties generate electric current due to photovoltaic effect, thereby realizing solar power generation effect. Among OPV devices, bulk heterojunction organic solar cells are the most widely used and have strong designability. The active layer of the bulk heterojunction organic solar cell is a bicontinuous and interpenetrating network structure formed by blending the donor material and the acceptor material. This structure greatly increases the contact area between the donor material and the acceptor material, reduces the diffusion distance of excitons, and greatly improves the energy conversion efficiency of OPV. For bulk heterojunction organic solar cells, the choice of acceptor and donor materials is very important and affects the performance of the cell. Common acceptor materials include fullerene derivative acceptor materials, perylene diimide derivative acceptor materials, fluorene acceptor materials, pyrrole acceptor materials and polymer acceptor materials. These acceptor materials generally have excellent optical, thermal and chemical stability, large conjugated planar structures, and excellent electron affinity and mobility. Acceptor materials with excellent performance can greatly improve the stability, energy conversion efficiency and lightness of OPV devices, making OPV devices develop towards the field of light, thin and high efficiency.
- Andrew J. Ferguson, Jeffrey L. Blackburn, Nikos Kopidakis. Fullerenes and carbon nanotubes as acceptor materials in organic photovoltaics [J]. Mater. Lett., 2013, 90, 115-125.