Theoretical design of Zn-dithiaporphyrins as sensitizer for dye-sensitized solar cells

Abstract

We have designed zinc dithiaporphyrin structures based on donor–π-acceptor (D-π-A) strategy and studied their optoelectronic properties as sensitizer for dye sensitized solar cells (DSSC) applications. The geometries, HOMO-LUMO energy gap, electronic absorption spectra and light harvesting efficiency (LHE) of these sensitizers were investigated by density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations. Our results showed that LUMO energies of all dyes are above the conduction band (CB) of TiO2 and the HOMO energies of them are below the redox couple of I−/I3−, thus new sensitizers have convenient HOMO and LUMO energy levels for electron transfer from the excited dye to TiO2 semiconductor and dye regeneration. They also have broadened and red-shifted absorption bands. Open-circuit voltage (Voc) and the short-circuit current density (Jsc) parameters including LHE, electron injection driving force (ΔGinject) and the free energy change for dye regeneration (ΔGregen) were calculated and discussed. The excited and ground state dipole moments were also calculated and their differences (ΔμEX−GS) were discussed. Finally, results showed that thiophene and benzothiadiazole rings in comparison with phenyl ring as π-bridge and cyanoacrylic acid relative to the carboxylic acid as acceptor and anchoring groups showed better efficiency. A general comparison of our new sensitizers with reference dyes (YD2-o-C8 and SM315) showed that new sensitizers can be used for DSSC applications.