Dopant‐Free Pyrrolopyrrole‐Based (PPr) Polymeric Hole‐Transporting Materials for Efficient Tin‐Based Perovskite Solar Cells with Stability Over 6000 h

Abstract A new set of pyrrolopyrrole‐based (PPr) polymers incorporated with thioalkylated/alkylated bithiophene (SBT/BT) is synthesized and explored as hole‐transporting materials (HTMs) for Sn‐based perovskite solar cells (TPSCs). Three bithiophenyl spacers bearing the thioalkylated hexyl (SBT‐6), thioalkylated tetradecyl (SBT‐14), and tetradecyl (BT‐14) chains are utilized to examine the effect of the alkyl chain lengths. Among them, the TPSCs are fabricated using PPr‐SBT‐14 as HTMs through a two‐step approach by attaining a power conversion efficiency (PCE) of 7.6% with a remarkable long‐term stability beyond 6000 h, which has not been reported elsewhere for a non‐PEDOT:PSS‐based TPSC. The PPr‐SBT‐14 device is stable under light irradiation for 5 h in air (50% relative humidity) at the maximum power point (MPP). The highly planar structure, strong intramolecular S(alkyl)···S(thiophene) interactions, and extended π‐conjugation of SBT enable the PPr‐SBT‐14 device to outperform the standard poly(3‐hexylthiophene,‐2,5‐diyl (P3HT) and other devices. The longer thio‐tetradecyl chain in SBT‐14 restricts molecular rotation and strongly affects the molecular conformation, solubility, and film wettability over other polymers. Thus, the present study makes a promising dopant‐free polymeric HTM model for the future design of highly efficient and stable TPSCs.