Designing small molecule hole transport materials for high hole mobility by core structure substitution: a DFT investigation

Hole transport materials (HTMs) are indispensable for achieving high-performance perovskite optoelectronic devices. We have designed hole transport layer materials, and the geometries, electronic properties, excited state properties, and carrier mobilities of the promising experimental HTM molecule PCA-2 and designed molecules based on PCA-2 by substituting the core structures (named DMS, DMC, DMN and DMO) have been theoretically investigated by employing quantum chemistry methods. Our results show that all the HTMs exhibit excellent planarity and light absorption properties, which are beneficial for facilitating intramolecular charge transfer and enhancing device short-circuit current. The stability of all the studied HTMs was better than that of Spiro-OMeTAD. Additionally, the designed molecules exhibit good capability of hole injection, with DMC, DMN and DMO also displaying effective electron-blocking ability. The solubility of DMN surpasses that of all other molecules. Among the designed HTMs, the hole mobilities of all HTMs except for DMC, are improved compared with the experimental molecule PCA-2. Notably, DMN not only exhibits energy levels matching with perovskite but also has the largest hole mobility, which gives it the potential to be an ideal HTM. This comprehensive study will provide insights into charge transport materials for perovskite optoelectronic devices.