Tuning the electronic and optical properties of Pt(diimine)(dithiolate) complexes through different anchoring groups; A DFT/TD-DFT study

Abstract

The development of novel anchoring groups is important for the effective utilization in dye-sensitized solar cells (DSSC). Among metal complex sensitizer, Pt(II) diimine dithiolate (PtN2S2) complexes have been proposed as alternative sensitizers owing to their ultimate photophysical and photochemical properties. Herein, a series of [Pt(bpy)(bdt)] sensitizers with different anchoring groups on the bpy (diimine) ligand have been designed and their geometrical, electronic, and photophysical properties for DSSC applications have been systematically examined both in the presence and absence of a solvent using density functional theory (DFT) and time dependent density functional theory (TD-DFT) methods. A precise electronic structure is also presented on the basis of NBO analysis. The seven anchoring groups are considered including aldehyde (1), hydroxamate (2), cyanoacrylic acid (3), carboxylic acids (4a−4c), boronic acid (5), phosphonic acids (6a−6c), and sulfonic acid (7) substituents. The results indicate that the gap energy (HLG) and electrophilicity (ω) values obtained for these structures alter by anchor addition. Notably, the anchors 1 and 7 have remarkable effect on the electronic features of [Pt(bpy)(bdt)] sensitizer. From the TD-DFT calculations, it is found that the substitution of the considered anchoring groups enhances the intensity of the absorption and the overall absorption spectrum can be red shifted significantly by lowering the LUMO energy. Besides, the values of light-harvesting efficiency (LHE) have calculated and compared with each other. These findings highlight the importance of using anchors 1 and 7 to boost the LHE of DSSCs. Thus, our results may give a useful guidance for the molecular design of the metal complex sensitizers used in DSSCs.