Utilizing a Carbazole-Incorporated Regioisomeric Synthesis Strategy to Design Hole Transporting Materials for Perovskite Solar Cells

Two new p-type molecules, namely TAT-TY3 and TAT-TY4, featuring triazatruxene endcaps and carbazole π-bridges, were synthesized. The photophysical and electrochemical properties of synthesized materials were comparatively investigated based on their 2,7- and 3,6-carbazole conjugation pathways. Optical characterizations revealed the impact of non-bonding electron delocalization of triazatruxene through carbazole moieties, resulting in a significant increase in absorption intensity corresponding to n-π* energy transitions and a red shift of triazatruxene moieties. Consequently, the optical band gaps of TAT-TY3 and TAT-TY4 were measured at 3.0 and 3.2 eV, respectively. Moreover, the molecules′ first oxidation potentials exhibited a drastic difference due to the electrochemical behavior of 2,7- and 3,6-carbazole moieties. The highest occupied molecular orbital (HOMO) level for TAT-TY3 was measured to be −5.02 eV, while for TAT-TY4, it was measured as −4.67 eV. Hole-extraction properties were explored using steady-state and time-resolved photoluminescence spectroscopy, revealing enhanced charge transfer between the TAT-TY3/Perovskite interface due to the better alignment of HOMO energy levels. The photovoltaic performances of the hole-transporting materials (HTMs) were successfully characterized in triple-cation perovskite solar cells and efficiencies of up to 17.9 %, 16.2 %, and 9.8 % were achieved for Spiro-OMeTAD, TAT-TY3, and TAT-TY4, respectively.