Influence of internal acceptor and thiophene based π-spacer in D-A-π-A system on photophysical and charge transport properties for efficient DSSCs: A DFT insight

A series of D-A-pi-A organic dyes are taken into consideration to study the influence of different internal acceptor groups and thiophene based pi-spacers on their efficiency in dye-sensitized solar cells (DSSCs). Density functional theory (DFT) and time-dependent density functional theory (TDDFT) methods are used for investigating the electronic excitations along with their geometrical and charge transport properties. HOMO, LUMO energy levels and HOMO LUMO energy gap helped in the understanding of energy levels appropriate for electron injection, electron transfer and dye regeneration. Thereafter, the calculations for short circuit current density (J(SC)) were performed by considering injection driving force (Delta G(inj)), dye regeneration energy (Delta G(reg)) and light-harvesting efficiency (LHE). In addition to this, charge transport properties like electron reorganization energy (lambda(h)), hole reorganization energy (lambda(e)), electron affinity (EA) and ionization potential (IP) are also reported. The results show that the insertion of internal acceptor in D-pi-A system and variation in the length of pi-spacer results in red-shifted absorption along with improved photovoltaic properties. Hence, the main purpose of this present study is to provide a theoretical background for proper designing and structural modifications in the development of efficient dyes in dye-sensitized solar cells (DSSCs).