Abstract
Since, the organic dyes that harness sunlight are generally considered as the heart of the dye sensitized solar cells (DSSC), the present study was carried out with the aim to design heterocyclic azo dyes that can be potentially used in DSSC application. Hereby, the analysis based on density functional theory (DFT) and time-dependent DFT calculations of the geometries, electronic structures and absorption spectra of the dyes before and after binding to titanium oxide (TiO2) were carried out and investigated in detail. The data obtained from these analyses were then used to determine the open-circuit photovoltage (V-OC), and to measure the important parameters such as the light harvesting efficiency (LHE) and the electron injection efficiency associated with the short-circuit photocurrent density (J(SC)). Our investigation reveals that all dyes showed absorbance in the visible region (469-521 nm) with high oscillator strength (f) (1.076-1.564) and LHE (0.9176-0.973). Moreover, we found that the dyes after binding to titanium oxide displayed slightly red-shifted absorption (475-527 nm) with improved oscillator strength (f) (1.121-1.664) and LHE (0.921-0.979). In addition, all dyes showed high V-OC (1.068-2.232 eV) and high driving force for the electron injection, thus leading to the larger J(SC). Our findings indicate that the heterocyclic azo dyes investigated in the current study can display better light to power conversion efficiency if used in the DSSC system, where the origin or their better performance can be attributed to the high J(SC) and V-OC values found for these potential dyes. Based on the detailed study and investigation, we believe that the theoretical criteria used in the present study can be employed as an initial screening tool not merely to assess the properties of other organic dyes, but also to potentially design the organic azo dyes for their potential application in the DSSC systems.