Pyridyl-functionalized spiro[fluorene–xanthene] as a dopant-free hole-transport material for stable perovskite solar cells

Abstract

Hole-transport materials (HTMs) play a critical role in perovskite solar cells (PSCs) for achieving high efficiency and stability. Herein, we have designed and synthesized an HTM named SPS-SPX-2TPA and studied its photovoltaic performance for PSC applications. The molecule SPS-SPX-2TPA consists of pyridyl substitution at para-position attached with a spiro[fluorene-9,9′-xanthene] (SFX) moiety as a central core unit and finally end capped with an N,N-dimethoxytriphenylamine (TPA) moiety. The synthesized SPS-SPX-2TPA HTM is three times cheaper than the most commonly used Spiro-OMeTAD HTM. Mesoporous PSCs fabricated using SPS-SPX-2TPA as the HTM showed the best power conversion efficiency (PCE) of 17.39% and 16.22% (device area 0.10 cm²) in forward and reverse bias, respectively. Moreover, the SPS-SPX-2TPA-based PSCs showed a stable photovoltaic performance of up to 270 h when measured under light soaking and maintained 95% of their initial PCE even after 600 h when measured under maximum power point tracking conditions with high reproducibility.