Engineering High-Performance Carbazole-Based Co-Sensitizers: Synthesis, Photophysical Characterization, and Synergistic Enhancement in Dye-Sensitized Solar Cells

The current research implies the synthesis of two novel organic co-sensitizers based on carbazole, which are referred to as MA-1 and MA-2. The performances of these sensitizers in dye-sensitized solar cells (DSSCs) were also studied. The molecular structures were designed using donor-π-acceptor (D-π-A) configurations, where 9-heptyl carbazole and 9-ethyl carbazole served as donors and malononitrile (MA-1) and cyanoacetic acid (MA-2) acted as acceptor/anchoring groups. The photophysical features of the sensitizers were evaluated via UV-Vis spectroscopy, revealing broad absorption in the visible range with λ_max at 468 nm (MA-1) and 478 nm (MA-2) and corresponding molar extinction coefficients of 3.76 × 10⁴ M⁻¹cm⁻¹ and 5.34 × 10⁴ M⁻¹cm⁻¹, respectively. Electrochemical analysis showed favorable ground state oxidation potentials (GSOP) and excited state oxidation potentials (ESOP) for both dyes, with optical band gaps of 2.44 eV (MA-1) and 2.28 eV (MA-2). These values indicate efficient electron injection into the TiO₂ conduction band and thermodynamic feasibility for dye regeneration. Co-sensitization using the benchmark N3 dye significantly enhanced the photovoltaic performance. The (MA-2 + N3) achieved the highest power conversion efficiency (PCE) of 9.82%, with a short-circuit current density (J_SC) of 23.91 mA/cm², an open-circuit voltage (V_OC) of 685 mV, and a fill factor (FF) of 0.60. This superior performance can be attributed to the synergistic interactions between the dyes, broader spectral coverage, and improved charge separation dynamics. By utilizing synergistic co-sensitization strategies, these findings shed light on the capacity of carbazole-based co-sensitizers, particularly MA-2, as potential candidates for high-efficiency DSSCs.