End-Group Modulation in a High Electron Mobility Y-Series Nonfullerene Acceptor Achieved Based on the DFT Method

The joining of Y6 has effectively promoted the power conversion efficiency (PCE) of organic solar cells, and the impact of its end-group modification on the PCE is significant. Here, eight different groups are introduced to modify the end-group of Y6, forming eight acceptors named V1, V2, V3, V4, V5, V6, V7, and R. The excited states, light absorption properties, and intermolecular electron transfer are discussed by the density functional theory. The density of state, average local ionization energy, Hirshfeld population, ionization potential, electron affinity, and electron mobility are also calculated. Results show that V7 obtains the largest red-shift in the UV-visible absorption spectra (787.55 nm). V7 and V5 have better electronic coupling while exhibiting the leading electron mobility (0.9577 and 0.4383 cm² V^-1 s^-1). Acceptors with rigid skeletons, good planarity, minimal steric hindrance, and locally uniform ALIE distributions have the potential to achieve higher electron mobility. These results indicate that precise end-group engineering can effectively regulate the electron mobility of acceptors, thereby increasing the PCE.