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

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-n-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 n-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 n-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.