Azatruxene-Based, Dumbbell-Shaped, Donor-pi-Bridge-Donor Hole-Transporting Materials for Perovskite Solar Cells

Three novel donor-pi-bridge-donor (D-pi-D) hole-transporting materials (HTMs) featuring triazatruxene electron-donating units bridged by different 3,4-ethylenedioxythiophene (EDOT) pi-conjugated linkers have been synthesized, characterized, and implemented in mesoporous perovskite solar cells (PSCs). The optoelectronic properties of the new dumbbell-shaped derivatives (DTTXs) are highly influenced by the chemical structure of the EDOT-based linker. Red-shifted absorption and emission and a stronger donor ability were observed in passing fromDTTX-1toDTTX-2due to the extended pi-conjugation.DTTX-3featured an intramolecular charge transfer between the external triazatruxene units and the azomethine-EDOT central scaffold, resulting in a more pronounced redshift. The three new derivatives have been tested in combination with the state-of-the-art triple-cation perovskite (FAPbI(3))(0.87)(MAPbBr(3))(0.13)CsPbI3in standard mesoporous PSCs. Remarkable power conversion efficiencies of 17.48 % and 18.30 % were measured forDTTX-1andDTTX-2, respectively, close to that measured for the benchmarking HTM spiro-OMeTAD (18.92 %), under 100 mA cm(-2)AM 1.5G solar illumination. PSCs withDTTX-3reached a PCE value of 12.68 %, which is attributed to the poorer film formation in comparison toDTTX-1andDTTX-2. These PCE values are in perfect agreement with the conductivity and hole mobility values determined for the new compounds and spiro-OMeTAD. Steady-state photoluminescence further confirmed the potential ofDTTX-1andDTTX-2for hole-transport applications as an alternative to spiro-OMeTAD.