Sb2S3 solar cells with a cost-effective and dopant-free fluorene-based enamine as a hole transport material

Antimony sulphide (Sb2S3) is a promising candidate for semi-transparent and tandem solar cells owing to its suitable optoelectronic properties. However, the applications of Sb2S3 solar cells are rather limited by their low power conversion efficiencies (PCEs) and use of expensive hole transport materials (HTMs). Furthermore, HTMs like P3HT exhibit parasitic absorption and hinder overall transparency of the devices. To circumvent these problems, V1236, a fluorene-based enamine is explored for the first time for Sb2S3 solar cells, which is significantly cheaper, transparent, and does not require high temperature activation like P3HT. Solar cells are fabricated in the glass/FTO/TiO2/Sb2S3/HTM/Au configuration wherein TiO2 and Sb2S3 are deposited using ultrasonic spray pyrolysis and HTMs are spin coated. The concentration of V1236 is systematically varied and its impact on the Sb2S3 device performance is investigated. The J(SC) of the solar cells with V1236 is about 17% higher which is attributed to the better valence band edge alignment compared to P3HT. The EQE measurements show no parasitic absorption with V1236 while the optical studies show a larger bandgap for V1236 (2.6 eV) over P3HT (1.8 eV), indicating negligible loss of transparency. Furthermore, the overall transparency is increased by 20% for V1236 devices in comparison to P3HT devices while yielding better PCEs, demonstrating the efficacy of novel V1236 as an HTM for semi-transparent Sb2S3 solar cells.