The influence of noncovalent interactions in metal-free organic dye molecules to augment the efficiency of dye sensitized solar cells: A computational study

The efficiency of dye sensitized solar cells (DSSCs) can be enhanced with achieving better planarity of metal-free organic dye molecules and thinning of their aggregation on the semiconductor surface. We report that the subtle noncovalent (NS)-S-... interaction between the substituted phosphazene group and thiophene spacer unit in dye molecule which induces the desired planarity and avoid aggregation of such molecules on the TiO2 surface using DFT calculations. DFT results show that phosphazene group increases the maximum absorption wavelength ((max)), driving force for electrons injection (G(injection)), singlet excited state lifetime (), dipole moments ((normal)), and number of electrons transferred from dye to TiO2 surface (q), which are known to augment the efficiency of DSSCs. Further, the lower G(regeneration) value of phosphazene containing dyes (e.g., -.37 eV, dye 2) than the reported dyes (e.g., -.81 eV, dye 1) indicate the faster electron injection rate from the former dye to the semiconductor TiO2. The role of phosphazene group to prevent the aggregation of dye molecules on the TiO2 anatase surface was also examined with GGA-PBE/DNP level of theory. The calculated results suggest that the dye molecules on 1-(TiO2)(38) and 2-(TiO2)(38) anatase clusters avoids the aggregation due to the steric congestion induced by phosphazene group. This work reports to accomplish dual properties with subtle noncovalent interactions in dye molecules to augment the efficiency in DSSCs.