Metallo-dithiaporphyrin pigments for bulk-heterojunction solar cell applications: ab initio investigation of structural and optoelectronic properties

Abstract

Metallo-dithiaporphyrin small molecules have been designed by substituting Ru(II) with various transition metals at the same oxidation state (M = Mn, Fe, Ni, Cu) as donor materials for Bulk Heterojunction Organic Solar Cells (BHJ-OSCs). Density functional theory (DFT) and time-dependent DFT (TD-DFT) have been used to study the optoelectronic properties of metallo-dithiaporphyrin at various functionals and basis sets. We discovered that the open-circuit voltage (V_OC) value increases when Ru(II) in Ru(S₂TTP)Cl₂ (S₂TTP = tetra-p-tolyldithiaporphyrin) is substituted. In addition, the light harvesting efficiency (LHE) of nickel, manganese, and iron complexes was found to be similar to that of ruthenium, and the iron complex furthermore presented a comparable charge transfer in the excited state corresponding to the Q-band, compared to Ru(S₂TTP)Cl₂. Hence M(S₂TTP)Cl₂ (M = Mn, Fe, Ni) appear to be potential low cost candidate donor molecules within a bulk heterojunction solar cell. We further propose suitable engineered acceptor pigments, fitted to provide a good overall solar cell efficiency.