Time-dependent properties and major electronic transitions in diphenylbacteriochlorin as a dye in DSSC: A quantum chemistry study

A metal-free type organic molecule, LS-00, based on bacteriochlorin macrocyclic structure (figure 1) has been investigated. In order to estimate the light harvesting efficiency (LHE) of the corresponding molecule [1], the excited states were obtained through the time-dependence density functional theory (TD-DFT) at M06-2X/6-311++G(d,p) level of theory [2]. According to the calculated spectroscopic properties, the studied molecule covers a wide range of sunlight. It is favorable to extend different designs of sensitizers derived from its structure to apply in the dye-sensitized solar cells (DSSCs) [3]. LS-00 can absorb the wavelengths from 287 to 648 nm. LS-00 has two maximum peaks, which one of them appears in the UV area (ɛ=9*104) and another peak in the visible area (ɛ=1*104). Also, it has the highest ability to harvest the wavelengths of 334.6 and 647.1 nm. Moreover, to find which electronic transfer is determinative for the spectroscopic properties, major electronic transitions in the excited states of the LS-00 structure were investigated. Results show the HOMO, HOMO -1, LUMO and LUMO -1 play key roles in the simulation of the UV-Vis spectrum. For example, in the visible area, the electronic transitions such as HOMO -1→ LUMO +1 and HOMO → LUMO are important, while in the UV area, the electronic transitions of HOMO -1→ LUMO and HOMO → LUMO +1 are outstanding.