New Carbazole-Based Sensitizers for p-Type DSSCs: Impact of the Position of Acceptor Units on Device Performance

Abstract

We report the design, synthesis, and characterization of two new carbazole-based organic dyes PC<inf>1-2</inf>as potential sensitizers for NiO-based p-type dye-sensitized solar cells (p-DSSCs). The D-A-π-A' configured PC<inf>1</inf>dye comprises a thienyl unit as a π-spacer and a malononitrile as an end-capping acceptor unit, whereas in PC<inf>2</inf>the cyanovinylene group serves as an acceptor unit and a thienyl group acts as a donor unit in a D-A-D 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, establishing structure-property relationships. PC<inf>1-2</inf>exhibit λ<inf>abs</inf>and λ<inf>emi</inf>in the range of 389-404 and 448-515 nm, respectively, with a band gap in the range of 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 PC<inf>1</inf>skeleton endows it with a higher dye loading capacity, high hole injection, and a strengthened intramolecular charge transfer (ICT) effect, resulting in a redshifted ICT absorption with a higher molar extinction coefficient. Among the two new dyes, the device based on PC<inf>1</inf>achieved the highest power conversion efficiency (PCE) of 0.027% with a short-circuit current density (J<inf>SC</inf>) of 1.29 mA·cm-2, open-circuit voltage (V<inf>OC</inf>) of 67 mV, and fill factor (FF) of 31%, whereas the device with dye PC<inf>2</inf>performed less efficiently (PCE: 0.018%, J<inf>SC</inf>: 0.92 mA·cm-2, V<inf>OC</inf>: 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. © 2022 American Chemical Society. All rights reserved.