Carbazole based organic dyes as effective photosensitizers: A comprehensive analysis of their structure-property relationships

Abstract

The present work describes the effect of structural modification of carbazole-based photosensitizers carrying carboxylic acid as a common anchoring functionality, on the photovoltaic parameters of newly fabricated DSSCs. In this study, we have selected our previously reported three carbazole-based derivatives, viz. S<inf>1-3</inf> having different structural designs, that is, D-π-A (S<inf>1</inf>), D-D-π-A (S<inf>2</inf>), and A-π-D-π-A (S<inf>3</inf>) with different donor units and π-spacers, but an identical cyanoacetic acid anchoring unit. We have evaluated their optical, electrochemical, and photovoltaic behaviors in order to explore their structure-property relationships. Also, the theoretical investigations were performed to obtain a deeper understanding of their HOMO-LUMO levels, charge distribution in FMOs, directional flow of electrons within the push-pull type sensitizers, and optical behavior. Finally, the DSSCs were constructed by employing these dyes as sensitizers without any co-absorbents and the performance of the devices was evaluated by using illuminated current-voltage characteristics. Among the tested dyes, di-anchoring S<inf>3</inf> exhibited improved PCE of 3.77 % due to its strong adsorption on the TiO<inf>2</inf> surface that resulted in superior V<inf>OC</inf> of the cell. While the S<inf>2</inf> containing electron-releasing anisole as an auxiliary donor exhibited better J<inf>SC</inf> value leading to the optimum PCE of 3.73 % which is comparable to that of S<inf>3</inf>. Obviously, these results validate the role of the π-spacer and additional donor of the sensitizers on the overall performance of the DSSCs. © 2021 The Authors. Electrochemical Science Advances published by Wiley-VCH GmbH.