Auxiliary Acceptor Engineering in Dithieno[3,2‐b:2′,3′‐d]Pyrrole‐Based Dyes for High‐Efficiency DSSCs: A DFT and TD‐DFT Perspective on Charge Transfer and Photovoltaic Performance

ABSTRACT

The present investigation describes the design and theoretical evaluation of a new series of dithieno[3,2‐b:2′,3′‐d]pyrrole‐based dye molecules produced within a D‐A′‐π‐A framework for application in dye‐sensitized solar cells (DSSCs). Twelve dye molecules (G1–I4) have been designed by systematically combining three auxiliary acceptor units: benzo[c][1,2,5]thiadiazole (BTZ), 5,6‐difluorobenzo[c][1,2,5]thiadiazole (FFBTZ), and [1,2,5]thiadiazolo[3,4‐c]pyridine (TZP), with a diphenylamine donor, a π‐conjugated spacer, and four distinct terminal acceptors. The structural, electronic, optical, and charge‐transfer properties have been investigated using Density Functional Theory (DFT) and Time‐Dependent DFT (TD‐DFT). Auxiliary acceptors successfully modify the electronic structure and improve light absorption efficiency. All dyes have narrow band gaps (2.39 to 2.74 eV) and strong intermolecular charge‐transfer (ICT) transitions with absorption maxima ranging from 514.8 to 609.4 nm. CAA, CPA, and functionalization with DCI and DCBI units significantly improve ICT strength, red‐shift absorption spectra, and electron injection efficiency. The computed open‐circuit voltages ( V _oc ) range from 0.80 to 1.40 eV, with light‐harvesting efficiencies (LHE) reaching up to 96.52%. Photovoltaic analysis showed excellent performance, with short‐circuit current densities ( J _SC ) reaching 38.8 mA cm ^{− 2} and PCE up to 39.5%. These results confirm the strong potential of the proposed dyes as high‐efficiency sensitizers for next‐generation DSSCs.