title: How to regulate energy levels and hole mobility of spiro-type hole transport materials in perovskite solar cells.
abstract: Methoxyaniline-based organic small molecules with three-dimensional structure have been proven as the most promising hole conductor for state-of-the-art perovskite devices. A fundamental understanding of the electronic properties and hole transport behavior of spiro-CPDT analogues, which is dependent on the number and position of the -OCH3groups, is significant for their potential applications as hole transport materials of perovskite solar cells. Our results from density functional theory calculations indicate that meta-substitution is more beneficial to reduce the highest occupied molecular orbital (HOMO) levels of molecules compared with ortho- and para-substitution. Furthermore, the hole mobility can be improved by ortho-substitution or mixed ortho- and para-substitution. Most interestingly, it is found that the improvement in hole mobility is at the expense of raising the HOMO level of spiro-CPDT analogues. These results can be useful in the process of designing and synthesizing excellent hole transport materials with suitable HOMO levels and high hole mobility.
authors.affiliation: Key Laboratory of Cluster Science of Ministry of Education, Beijing Key Laboratory of Photoelectronic/Electrophotonic Conversion Materials, School of Chemistry, Beijing Institute of Technology, Beijing 100081, China. zeshengli@bit.edu.cn.
authors.forename: Wei-Jie
authors.initials: WJ
authors.lastname: Chi
authors.forename: Ping-Ping
authors.initials: PP
authors.lastname: Sun
authors.forename: Ze-Sheng
authors.initials: ZS
authors.lastname: Li