Low-Cost Dopant Additive-Free Hole-Transporting Material for a Robust Perovskite Solar Cell with Efficiency Exceeding 21%
Hongwei Zhu, Zhongjin Shen, Linfeng Pan, Jianlei Han, Felix T. Eickemeyer, Yameng Ren, Xianggao Li, Shirong Wang, Hongli Liu, Xiaofei Dong, Shaik M. Zakeeruddin, Anders Hagfeldt, Yuhang Liu, Michaël Grätzel
Abstract
Developing hole-transporting materials (HTMs) with appropriate molecular configuration and charge mobility is important to improve perovskite solar cell (PSC) photovoltaic performance and their feasibility for commercialization. In this work, a novel pyramidal-shaped low-cost HTM coded MeOTTVT is prepared through extension of π-conjugation based on a triphenylamine core. Carbon–carbon double bonds are introduced between the core and p-methoxyl triphenylamine to improve the planarity of the HTM, favoring intermolecular stacking of MeOTTVT and thus improving the hole mobility of the corresponding hole-transporting layer (HTL). The p-methoxyl triphenylamine-endowed HTM benefits from a highest occupied molecular orbital level well-aligned with the perovskite active layer, facilitating effective hole extraction. The champion PSC using an MeOTTVT-based dopant additive-free HTL yielded a power conversion efficiency (PCE) up to 21.30%, which is considered one of the best-performing PSCs employing a dopant additive-free small molecule HTM. In addition, the MeOTTVT-based dopant additive-free HTL exhibits outstanding thermal stability and high glass-transition temperature (Tg = 137.1 °C), combined with a more hydrophobic surface; PSCs based on an MeOTTVT dopant additive-free HTL exhibit outstanding stability against moisture, 1 sun illumination, and thermal stress.