title: A strategy to improve the efficiency of hole transporting materials: introduction of a highly symmetrical core.
abstract: The electronic, optical and hole transport properties of three new hole transporting materials (HTMs) with a planar core have been investigated by using density functional theory and Marcus theory. A reliable semi-rational formula was adopted to calculate the highest occupied molecular orbital (HOMO) levels of new HTMs. The results showed that the HOMO levels of new HTMs were 0.07-0.30 eV lower than those of Spiro-OMeTAD, and their absorption peaks appeared outside or close to the visible region and overlapped slightly with the absorption band of perovskites. Moreover, the Stokes shifts of the designing molecules were calculated to lie in a range from 72 to 124 nm, meaning that they could undergo large geometrical changes on excitation. More importantly, the hole mobility of new HTMs (0.099-0.27 cm2v-1s-1) was approximately two orders of magnitude higher than that of Spiro-OMeTAD (0.0056 cm2v-1s-1) due to strong hole coupling from a face-to-face packing pattern. Our results indicated that planar core-based HTMs could become potential candidates to replace the widely established Spiro-OMeTAD.
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.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: Ping-Ping
authors.initials: PP
authors.lastname: Sun
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: Ze-Sheng
authors.initials: ZS
authors.lastname: Li