Dopant-Free Pyrrolopyrrole-based (PPr) Polymeric Hole-Transporting Materials for Efficient Tin-based Perovskite Solar Cells with Stability over 6000 h.

A new set of pyrrolopyrrole-based (PPr) polymers incorporated with thioalkylated/alkylated bithiophene (SBT/BT) were 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 were utilized to examine the effect of the alkyl chain lengths. Among them, the TPSCs were 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 hours, which has not been reported elsewhere for a non-PEDOT:PSS-based TPSC. The PPr-SBT-14 device was stable under light irradiation for 5 hours 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 made the PPr-SBT-14 device outperform the standard P3HT and other devices. The longer thio-tetradecyl chain in SBT-14 restricts the 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. This article is protected by copyright. All rights reserved.