Near-infrared harvesting metal-free organic dyes for transparent DSSCs: A theoretical design approach

Abstract

In this study, we employed density functional theory (DFT) and time-dependent DFT (TD-DFT) calculations to optimize near-infrared (NIR) harvesting dyes, gaining deeper insights into their structure–property relationship, particularly for dye-sensitized solar cells (DSSCs). Our focus was on fine-tuning electron-donating and withdrawing groups within D-π-A metal-free organic dyes to enhance NIR absorption and achieve visually transparent DSSCs. Our research revealed a significant redshift in dyes based on isoindigo derivatives, with thiophene (TII) as the π-spacer. Dyes incorporating fluorene as the donor group effectively mitigated charge recombination rates, a key challenge in low-bandgap molecules. Notably, the TII1 dye, combining a fluorene donor with a TII π-spacer, exhibited maximum absorption at 654 nm and transmitted substantial visible light (500–600 nm), making it suitable for use in visually transparent DSSCs. These findings underscore the potential of the TII1 dye in significantly advancing the development of visibly transparent DSSCs.