Mechanism of charge separation and transfer in doped third-component enhanced organic solar cells

The preparation of ternary organic solar cells (T-OSCs) is an effective strategy to improve the device's performance. As a green and abundant organic semiconductor in nature, chlorophyll and its derivatives have excellent charge transfer capabilities. Here, we introduced the bacteriochlorin BChl-2 as the third component into the study system, and all the monomeric molecules, D/A interfaces and dimers were comprehensively investigated. It is shown that BChl-2 has a better structure and minimal ionization energy, indicating that it facilitates π-π stacking of molecules and hole injection. All the molecules exhibit complementary absorption spectra, which are beneficial to improve the short-circuit current (J_SC) of organic solar cells (OSCs). In addition, the doping of BChl-2 increases the charge transfer paths while forming D/A interfaces with a greater separation rate, further improving the charge transfer efficiency. The excellent charge mobility of BChl-2 greatly facilitates charge transfer, which is conducive to the improvement of the J_SC and fill factor (FF) of the devices. All these results indicate that doping BChl-2 can enhance the charge separation and transfer of OSCs. This study not only revealed the mechanism of the third component effect but also provided a referential scheme for designing efficient T-OSCs.