A low-cost dopant-free thiophene-based hole transport material for n–i–p perovskite solar cells†

Perovskite solar cells (PSCs) with dopant-free hole transporting layers (HTLs) have attracted wide attention owing to their excellent photoelectric conversion efficiency and environmental stability. However, the hole transporting materials (HTMs) used to prepare dopant-free HTLs seriously hinder the commercial development of PSCs because of their high production cost and complicated preparation process. Herein, we chose thiophene as the central core to synthesize two low-cost HTMs, namely S1 and S2. Owing to the introduction of the ethylene bridge, the conjugated structure of S2 was expanded, and the steric hindrance of triphenylamine was reduced, which endowed S2 with a higher carrier mobility of 1.83 × 10⁻⁴ cm² V⁻¹ s⁻¹ than that of S1 with 6.3 × 10⁻⁵ cm² V⁻¹ s⁻¹. Furthermore, the S2-based PSCs provided an excellent power conversion efficiency of 20.13%, which was higher than those of PSCs based on S1 (18.01%). Besides, PSC devices with S1 and S2 as dopant-free HTL maintained more than 85% of their initial efficiency in air for 60 days. This work not only enriches the material system of dopant-free HTMs but also provides a simple and effective strategy for the preparation of low-cost and high-performance HTMs, paving the way for the commercialization of PSCs with dopant-free HTLs.