Recent Advances in Poly(3‐hexylthiophene) and Its Applications in Perovskite Solar Cells

2,2',7,7'‐Tetrakis( N , N ‐di‐p‐methoxyphenylamine)‐9,9'‐spirobifluorene (Spiro‐OMeTAD) is considered the backbone of high performance in perovskite solar cells (PSCs) with the highest recorded power conversion efficiency near 26%. Devices with Spiro‐OMeTAD as a hole‐transport material (HTM) inherit very low stability due to the use of ionic‐based and unstable hygroscopic dopants to boost their hole mobility, hindering their stability. Poly(3‐hexylthiophene) (P3HT) is considered one of the promising HTM candidates, due to its formidable physical and electronic properties including higher hole mobility and thermal and moisture‐resisting nature. Despite these advantages, pristine P3HT‐based PSCs suffer low photovoltaic performances owing to unmatched perovskite/hole‐transport layer (HTL) interface and low mobility compared to doped HTMs. Today, studies are focusing on how to manage the interface between perovskite and P3HT and improve its hole mobility to achieve significant performance records in n– i –p PSCs. Herein, the advances of P3HT HTL are reviewed and light is shed on its different related approaches. Doping strategies and structural and molecular modifications to boost the hole mobility are reviewed. Interface engineering approaches to enhance the contact between perovskite and P3HT are discussed in detail. Moreover, incorporation in future PSC applications is investigated. Finally, a summary and a short outlook are provided.