Effect of bridged spacers and auxiliary acceptors on Dye Sensitized Solar Cell sensitizers: A density functional theory‐based investigation

Abstract

AbstractFour donor‐pi‐acceptor (D‐π‐A) type sensitizers containing coumarin as the donor unit and cyanoacrylic acid as the acceptor unit are investigated using density functional theory (DFT) and time‐dependent‐DFT methods. The effect of introducing auxiliary acceptor like benzothiadiazole and spacer bridge like 3,4‐ethylenedioxythiophene (EDOT) is analyzed. The EDOT bridge leads to increase in band gap whereas the introduction of benzothiadiazole lessens the band gap. The frontier molecular orbital diagram also shows an efficient intramolecular charge transfer for non‐EDOT based sensitizers. For benzothiadiazole‐based sensitizers, the electrophilicity index was higher and hyperhardness was lower in the estimated reactivity descriptors. The experimentally determined light harvesting efficiency (LHE) of the sensitizers is correlated with the calculated global descriptors. A direct relation of LHE is obtained with electrophilicity index and an inverse relation for hyperhardness. A reverse trend is seen on comparing these descriptors with the band gap of the sensitizers. The computed non‐linear optical (NLO) characteristics show that the benzothiadiazole acceptor increases NLO response, while EDOT‐based sensitizers show a reduced NLO response. The NLO properties also give a direct relation with the LHE and electrophilicity index. The hyperpolarizability exhibits an inverse relation with the transition energy which is in accordance with the Ouder's model.