Abstract
Dye-sensitized solar cells (DSSCs) have been widely investigated; however, the development of promising dye sensitizers is still appealing. In this work, we perform a detailed theoretical search for high-efficiency D-π-A organic dyes using density functional theory and time-dependent density functional theory calculations. Specifically, we perform geometric optimization, and electronic structure and absorption spectra calculations for isolated dyes for two thieno[3,2-b]benzothiophene π-spacer-based D-π-A organic dyes SGT129 and SGT130, which show significant efficiency difference, before and after binding to a TiO2 semiconductor. The calculation results reveal that the coplanar configuration between the electron donor and the π-spacer can enhance electronic communication efficiently, thus facilitating intra-molecular charge transfer from the electron donor to the acceptor groups in SGT130. The absorption spectrum of SGT130 broadens and is red-shifted owing to the decreased bandgap. The higher light-harvesting efficiency, favorable intra-molecular charge transfer, larger shift of the conduction band edge in the TiO2 semiconductor, and slower charge recombination between the injected electrons in the TiO2 conduction band and the electrolyte explain the superior efficiency of SGT130 over that of SGT129. Using SGT130 as the reference dye, we further design four novel dyes 1–4 by modifying the π-spacer with electron-rich and electron-withdrawing moieties. Judging from the theoretical parameters influencing the short-circuit current and open-circuit voltage, we found that all dyes would perform better than SGT130 in terms of the favorable interfacial charge transfer (ICT) and light-harvesting efficiency, as well as the larger shift of the TiO2 conduction band edge. Our theoretical research is expected to provide valuable insights into the molecular modification of TBT-based D-π-A organic dyes for DSSC applications.
Highlights
Depletion of fossil fuels and the resulting environmental issues have led to increased interest in the search for alternative energy sources
It has been widely accepted that the planar conformation of the π-bridge group ensures the good electronic communication between the electron donor and acceptor, as shown by the work of Li P. et al (2017a): We can expect that the torsion angles between the electron donor and π-bridge in SGT129 is larger than those in SGT130. this is due to the steric hindrance of the adjacent phenyl units from the TPA donor and TBT π-spacer
Both dyes exhibit highest occupied molecular orbital (HOMO) that are lower than the redox potential of I−/I−3, and lowest unoccupied molecular orbital (LUMO) that are higher than the conduction band edge of TiO2, guaranteeing the energetically favorable dye regeneration and electron injection
Summary
Depletion of fossil fuels and the resulting environmental issues have led to increased interest in the search for alternative energy sources. The solar cell, a device that converts solar energy into electricity, offers a valuable solution to this problem. Dye-sensitized solar cells (DSSCs) are prominent owing to their obvious advantages of low cost, high power conversion efficiency, and easy fabrication relative to Si-based solar cells (O’Regan and Grätzel, 1991; Grätzel, 2001). DSSCs have the following four primary parts: dye sensitizer, TiO2 semiconductor, electrolyte, and counter electrode. The dye sensitizer is crucial in the operation of DSSCs as it is responsible for the capture of photons and generation of photoexcited electrons. The excited electrons are subsequently injected to the semiconductor conduction band, leaving the oxidized dye for subsequent reduction by an electrolyte
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