Low-Cost Dopant Additive-Free Hole-Transporting Material for a Robust Perovskite Solar Cell with Efficiency Exceeding 21%

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.