Optoelectronic of Properties of N1-[4-(Diethylamino)phenyl]-N4,N4-diethyl-N1-(thiophen-2-yl)benzene-1,4-diamine-Based (D-A2-π-A) Dyes with Enzothiadiazole/Dihydrothieno[3,4-b][1,4]dioxine as Auxiliary Acceptor for DSSCs Applications: DFT/TD-DFT Approach

A series of N¹-[4-(diethylamino)phenyl]-N⁴,N⁴-diethyl-N¹-(thiophen-2-yl)benzene-1,4-diamine based (D-A2-π-A) organic dye-sensitizers with enzothiadiazole (DSN dyes)/dihydrothieno[3,4-b][1,4]dioxine (DSO dyes) as auxiliary acceptor were studied, emphasizing the influence of the π bridges on the DSSC’s efficiency. DFT and TD-DFT methods at B3LYP/6-31G** were used to calculate the molecular, optoelectronic and photovoltaic properties of the dyes such as Frontier orbital energies, chemical reactivity indices, absorption wavelengths, light harvesting efficiency (LHE), electron injection driving force (ΔG^inject), regeneration drive force (ΔG^regen), open circuit voltage (V_oc) and excited state lifetime (τ_esl). The results of open circuit voltage (V_oc), light harvesting efficiency (LHE) and light electron injection driving force (ΔG^inject) show that all the dyes have good photoelectric conversion efficiency but with low dye regeneration (ΔG^regen) ability. The energy gap (E_g) has a major effect on the activity of molecules; thus, a sensitizer with a small E_g is more advantageous for electron excitation and has increased absorption properties. It was found that DSN dyes have lower E_g than corresponding DSO dyes. Therefore, DSN dyes are expected to have longer absorption wavelength (red shift) than respective DSO dyes. The DSN dyes show ease of electrons transfer through the dyes, which is linked to low values of chemical potential for DSO dyes. However, high excited state lifetime (τ_esl) values of some dyes could lead to more stability of the dyes in the cationic state for a longer time, which may result in higher charge transfer efficiency; thus enhancing electron injection efficiency of the dye sensitizers for dye-sensitized solar cell (DSSC).