Pyrrole – Best additional spacers for azo based dye sensitized solar cells: A computational study

• Additional heterocyclic spacers are important for a good dye sensitizer for the improvement of the efficiency for solar cells. • Quantum chemical calculations proposed the proper position of the additional spacers for azo based dyes and also the proper additional spacers. • Charge transfer analysis, light-harvesting efficiencies and driving forces like electron injections and dye regeneration for the free dye and dye-TiO 2 complex have been calculated using DFT and TDDFT. • Our methods suggested nitrogen based additional heterocyclic spacers to be the best additional spacer with high driving force leading to an increased efficiency for the dye sensitizer. Quantum chemical calculations have been performed in this article to study the effect of heterocyclic spacers on the azo based metal free Donor-π-Acceptor dyes. Six heterocyclic moieties were used as additional spacers in two different positions on a azo based dye to generate twelve different dye sensitizers and the progress on the optoelectronic properties and the efficiency of such dyes have been studied using density functional approach. According to our calculated properties like charge transfer analysis, light-harvesting efficiencies and driving forces like electron injections and dye regeneration for the free dye and dye-TiO 2 complex, nitrogen based additional heterocyclic spacers (Pyrrole) showed to be the best additional spacer with high driving force leading to an increased efficiency for the dye sensitizer.