Impact of Dopant‐Free Hole Transport Materials on the Performance of Layered Cs ₃ Sb ₂ I ₉ Perovskite Solar Cells

Perovskite solar cells (PSCs) have rapidly advanced in photovoltaic research, achieving power conversion efficiencies up to 27%. However, the toxicity of lead (Pb) and the inherent instability of these materials hinder their commercial adoption. To address these issues, Pb‐free perovskites such as layered (2‐dimensional) cesium antimony iodide (Cs 3 Sb 2 I 9 ) have been investigated for their environmental compatibility and promising optoelectronic properties. However, their efficiencies remain lower than those of Pb‐based analogs, and stability is still a challenge. A significant contributor to device instability is the use of doped hole‐transport materials, where hygroscopic dopant salts promote moisture ingress and accelerate degradation. Herein, we examine the influence of dopant‐free hole transport materials, P3HT, PTB7, and CuSCN, on the performance and stability of layered Cs 3 Sb 2 I 9 PSCs. Planar devices incorporating PTB7 and CuSCN achieved power conversion efficiencies (PCEs) of 2.05% and 2.26%, respectively, while P3HT yielded the highest PCE of 2.44%, ranking among the best efficiencies reported for this type of solar cell. These findings highlight the potential of dopant‐free HTMs to enhance both efficiency and stability in lead‐free PSCs.