Near-IR phenothiazine–squaraine photosensitizers: unveiling an acid–base co-sensitization strategy toward 12.11% efficient DSSCs

Herein, the rational design, synthesis and characterization of two phenothiazine-squaraine hybrid sensitizers (PS-1 and PS-2) were reported. The sensitizers contain phenothiazine, dithiophene and squaraine-indoline as the donor, π-bridges and electron-withdrawing segments, respectively. PS-1 contains a Lewis-basic nitrile (-CN), while PS-2 contains a Brønsted-acidic carboxylic acid (-COOH) as anchoring groups. UV-vis absorption spectroscopy, cyclic voltammetry (CV), dye-sensitized solar cell (DSSC) device evaluation, and computational calculations were systematically performed. Both PS-1 and PS-2 display narrow bandgap energies of 1.87 and 1.90 eV, enabling broad visible-to-near-infrared (NIR) absorption and strong intramolecular charge-transfer characteristics with absorption maxima approximately 657 nm and 650 nm respectively. Despite the superior photophysical and electrochemical properties of PS-1, PS-2-based device displayed slightly higher power conversion efficiency (η) of 6.24% (JSC = 16.85 mA/cm2, FF = 0.612, VOC = 0.606 V) compared to PS-1 (η = 5.73%) due to stronger anchoring interactions with TiO2. Furthermore, a rational acid-base co-sensitization strategy employing PS-1 and PS-2 resulted in an enhanced efficiency of 7.80% arising from synergistic complementary absorption and improved molecular packing on the TiO2 surface. Notably, the acid–base co-sensitized system combining PS-1 with N719 achieved the highest η of 12.11% which is attributed to improved light harvesting, suppressed recombination, and a higher Jsc of 23.70 mA cm−2. Collectively, these results confirm that complementary acid–base adsorption provides an effective strategy for simultaneously optimizing surface coverage and enhancing DSSC efficiency and operational stability.

Text 125898.pdf - Published Version Restricted to Repository staff only Download (7MB) Official URL or Download Paper: https://linkinghub.elsevier.com/retrieve/pii/S0143...

Actions (login required)

View Item