New Carbazole-Based Sensitizers for p-Type DSSCs: Impact of the Position of Acceptor Units on Device Performance
Résumé
We report the design, synthesis, and characterization of two new carbazole-based organic dyes PC1-2 as potential sensitizers for NiO-based p-type dye-sensitized solar cells (p-DSSCs). The D-A-π-A configured PC1 dye comprises a thienyl unit as a π-spacer and a malononitrile as an end-capping acceptor unit, whereas in PC2 the cyanovinylene group serves as an acceptor unit and a thienyl group acts as a donor unit in a D-AD configuration. These molecules achieved excellent solubility due to their long-branched alkyl chains. The current work encompasses their structural, photophysical, thermal, electrochemical, theoretical, and photoelectrochemical studies allowing establishing of structure-property relationships. PC1-2 exhibit λabs and λemi in the range of 389-404 nm and 448-515 nm, respectively, with a bandgap in the order, 2.88-2.92 eV. Electrochemical studies confirm the feasibility of electron injection, regeneration, and recombination. The introduction of an additional electron withdrawing group (cyanovinylene group) on the dye PC1 skeleton endows with a higher dye loading capacity, high hole injection, and a strengthened ICT effect, resulting in a red-shifted ICT absorption with a higher molar extinction coefficient. Among the two new dyes, the device based on PC1 achieved the highest power conversion efficiency (PCE) of 0.027% with short-circuit current density (JSC) of 1.29 mA⸳cm-2 , opencircuit voltage (VOC) of 67 mV, and fill factor (FF) of 31%, whereas the device with dye PC2 performed less efficiently (PCE: 0.018 %, JSC: 0.92 mA⸳cm-2 , VOC: 68 mV, and FF: 30 %). Conclusively, the study provides insights into the intricacies involved in the structural modification of carbazole-based p-type dyads for the development of highly efficient DSSCs.
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