Hole transport materials (HTMs) play essential roles in achieving high photovoltaic performance and long‐term stability in the n–i–p structure of perovskite solar cell (PSC) devices. Recently, dopant‐free polymeric materials as HTMs in PSCs have attracted considerable attention owing to high carrier mobility and excellent hydrophobicity. However, achieving similar efficiencies to those of doped small molecule HTMs such as Spiro‐OMeTAD is a big challenge. Herein, a thienothiophene π‐bridge is selected as a stabilizer and energy level regulator incorporated into a donor–acceptor‐type HTM to synthesize a new polymer, Nap‐SiBTA. The incorporation of the thienothiophene group improves the thermal stability and favors the high planarity and face‐on orientation, promoting high charge carrier mobility and tunable optical band gap. Finally, the dopant‐free polymer Nap‐SiBTA‐based PSC achieves an excellent power conversion efficiency (PCE) of 23.07% with a high fill factor of 80.85%. To the best of the authors’ knowledge, this is one of the best efficiencies in dopant‐free HTM PSCs. Moreover, the unencapsulated device retains 93% of its initial PCE after 1000 h owing to the excellent hydrophobicity of Nap‐SiBTA. This work provides a general and practical method to design dopant‐free HTMs for the high efficiency and long‐term stability of PSCs.

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FA1 − XCsXPbI3 (formamidinium [FA]; cesium [Cs]; lead [Pb]; and iodine [I]) perovskites are promising candidates in perovskite solar cells (PSCs) for the superior optoelectronic properties, tunable bandgap, and high thermal stability. It is well known that the preparation of phase‐pure perovskite and hybrid cations and/or halides strategy are effective ways to achieve high efficiency and strengthen the stability of PSCs. In this work, dual cation perovskite precursor Cs0.05FA0.95PbI3 was synthesized by a simple and effective one‐step solution process under ambient conditions and successfully used in the PSCs as an active layer. By this strategy, the high‐purity Cs‐FA hybrid cations perovskites not only enhanced power conversion efficiency (PCE) to 22.10% but also achieved long‐term stability. This work explains in detail the effects of Cs+ in FAPbI3 perovskites on precursor chemistry, film nucleation, grain growth, and defect properties. Furthermore, with the incorporation of MACl in the precursor and passivation process, the photovoltaic properties are further enhanced. Encouragingly, the mixed cations PSCs feature the champion PCE of 24.5%, which is one of the highest values reported to date for Cs‐doped PSCs.

Synchronously achieving high power conversion efficiency (PCE) at low cost is a great challenge for the star hole transport material (HTM) Spiro-OMeTAD-based perovskite solar cells (PSCs) because of their expense....