Rational Design of Cyclopenta[2,1-b;3,4-b′]dithiophene-bridged Hole Transporting Materials for Highly Efficient and Stable Perovskite Solar Cells

A series of small-molecule-based hole-transporting materials (HTMs) featuring a 4H-cyclopenta[2,1-b : 3,4-b′]dithiophene as the central core with triphenylamine- and carbazole-based side groups was synthesized and evaluated for perovskite solar cells. The correlations of the chemical structure of the HTMs on the photovoltaic performance were explored through different combinations of the central π-bridge moieties. The optical and electrochemical properties, energy levels, and hole mobility were systematically investigated, revealing the significant influence of the central core planarity and packing structure on their photovoltaic performance. The optimized device based on CT1 exhibited a PCE (power conversion efficiency) of 17.71 % with a device architecture of FTO/TiO ₂ compact layer/TiO ₂ mesoporous/CH ₃ NH ₃ PbI ₃ /HTM/MoO ₃ /Ag, which was found to be on par with that of a cell fabricated based on state-of-the-art spiro-OMeTAD (16.97 %) as HTM. Moreover, stability assessment showed an improved stability for CPDT-based HTMs in comparison with spiro-OMeTAD over 1300 h.