Tripodal Triazatruxene Derivative as a Face-On Oriented Hole-Collecting Monolayer for Efficient and Stable Inverted Perovskite Solar Cells
Minh Anh Truong, Tsukasa Funasaki, Lucas Ueberricke, Wataru Nojo, Richard Murdey, Takumi Yamada, Shuaifeng Hu, Aruto Akatsuka, Naomu Sekiguchi, Shota Hira, Lingling Xie, Tomoya Nakamura, Nobutaka Shioya, Daisuke Kan, Yuta Tsuji, Satoshi Iikubo, Hiroyuki Yoshida, Yuichi Shimakawa, Takeshi Hasegawa, Yoshihiko Kanemitsu, Takanori Suzuki, Atsushi Wakamiya
Abstract
Hole-collecting monolayers have drawn attention in perovskite solar cell research due to their ease of processing, high performance, and good durability. Since molecules in the hole-collecting monolayer are typically composed of functionalized π-conjugated structures, hole extraction is expected to be more efficient when the π-cores are oriented face-on with respect to the adjacent surfaces. However, strategies for reliably controlling the molecular orientation in monolayers remain elusive. In this work, multiple phosphonic acid anchoring groups were used to control the molecular orientation of a series of triazatruxene derivatives chemisorbed on a transparent conducting oxide electrode surface. Using infrared reflection absorption spectroscopy and metastable atom electron spectroscopy, we found that multipodal derivatives align face-on to the electrode surface, while the monopodal counterpart adopts a more tilted configuration. The face-on orientation was found to facilitate hole extraction, leading to inverted perovskite solar cells with enhanced stability and high-power conversion efficiencies up to 23.0%.