Augmentation in photocurrent through organic ionic plastic crystals as an efficient redox mediator for solid-state mesoscopic photovoltaic devices

Abstract

Mesoscopic photovoltaic devices (MPDs) are significantly promising for sustainable light-harvesting through solid-state compact designs. Materials with multifunctional properties play a vital role in improving the processability, stability, and cost of such devices. Here, a single-route synthesized sensitizer and multifunctional organic ionic plastic crystals (OIPCs) are introduced, and OIPCs are employed as a redox couple and light-harvesting contributor as a binary sensitizer-electrolyte system enabled via energy transfer in a photovoltaic device. Materials OIPC-I, OIPC-Br, and SK4 sensitizer possess a typical N-alkyl-phenoxazine (POZ)–N-alkyl-benzimidazole (BM)-type architecture, and OIPCs hold additional iodide and bromide anions at the quaternary nitrogen of BM. OIPCs show redox potential generated from anions corresponding to I⁻/I₃⁻ and Br⁻/Br₃⁻ as well as suitable molecular energy levels due to the POZ–BM donor–acceptor pathway, which results in a self-regenerative photovoltaic response in FTO/p-TiO₂/OIPC/Pt configuration without any sensitizer. The SK4 sensitizer has suitable energy levels below the redox potential level of OIPCs, which are well regenerated by OIPCs during the photo-electricity generation in the photovoltaic device. Here, an OIPC–Br-based device with high photovoltage (0.98 (±0.02) V) and pronounced photocurrent from extra electrons gained through the POZ donor present in OIPC by the energy transfer mechanism shows 45% energy transfer towards the dye or TiO₂. The OIPC-I based device demonstrated 43% (±3) higher efficiency compared to the conventional benzimidazolium-based electrolyte due to improved photocurrent and photovoltage. Single component OIPC-I based solid-state MPD devices show excellent ∼95% stability up to 5000 h, which is more than the OIPC–Br based device.