First Principles Study of Dendritic Carbazole Photosensitizer Dyes Modified with Different Conjugation Structures

Abstract

In the pursuit of efficient organic dyes first principles calculations were carried out by using density functional theory (DFT). The electronic and optical properties of D−D‐π‐A carbazole dendritic donor and cyanoacrylic acid acceptor conjugated through thiophene and oxadiazole structures are being reported. The findings of this work point to the dependence of the structural modifications especially changes in length of conjugation molecule appeared to notably affect the properties of the dyes. The positions of highest occupied molecular orbital (HOMO) and lowest molecular orbitals (LUMO) energy levels are found suitable for electron reduction and electron injection processes respectively. The addition of another oxadiazole ring as well as replacement of a thiophene ring with existing oxadiazole in the conjugating bridge appeared to reduce the HOMO‐LUMO energy gap. TD‐DFT excitation spectra calculated at PBE, B3LYP and CAM−B3LYP levels of theory are discussed in detail to shed light on charge transfer process in the dye molecules and the calculated results are found consistent with reported experimental work. The changes in length and structure of π‐spacer chain are discussed to analyze the photon to current conversion efficiency.

Time‐dependent density functional theory investigations on structural modification in carbazole‐based organic photosensitizers to improve electron injection in dye‐sensitized solar cell

“…The results of excitation spectra and optical transitions in D1, D2, and D3 have been reported elsewhere. [ 22 ] However, the description involving these dyes is given here for the sake of completeness with the addition of photoinjection and solvation effects involving these three dyes. The magnitudes of molecular dipole moment, calculated with analytic integration using PBE, were 1.680 for D1, 2.195 for D2, 2.246 for D3, 2.001 for D1A, 2.027 for D2A, and 1.769 for D3A.…”

“…The energies of LUMO and HOMO of D1 and D1A were obtained by utilizing ADF/TD‐DFT with the XC functional set as GGA‐PBE, Hybrid‐B3LYP and SCC‐DFTB. The respective values of HOMO of D1 are −5.0, −5.6 eV, [ 22 ] and −5.2 eV and LUMO are −3.9, −3.2 eV, [ 22 ] and −3.9 eV with band gaps of −1.1, −2.4, and −1.3 eV, calculated using GGA‐PBE, Hybrid‐B3LYP, and SCC‐DFTB. In case of D1A, the respective values of HOMO and LUMO are −4.9, −5.6, and −5.1 eV and −3.8, −3.2, and −3.8 eV, respectively, with same band gap as that of D1 calculated for all three functionals.…”

“…The HOMO of D2 is found to be −5.0, −5.6 eV, [ 22 ] and −5.2 eV and LUMO to be −4.1, −3.5 eV, [ 22 ] and −3.9 eV, with band gaps of −0.9, −2.1, and −1.3 eV calculated using‐PBE, Hybrid‐B3LYP, and SCC‐DFTB, respectively. On the other hand, the HOMO of D2A is found to be −5.0, −5.6, and −5.2 eV and LUMO level to be−4.0, −3.4, and −3.9 eV, with band gaps of −1.0, −2.2, and −1.3 eV calculated for three respective functionals.…”

“…To investigate the effects of the structural modification of carbazole donor‐based organic dye on photoinjection, three dyes, named here as D1, D2, and D3, shown in Figure 2, were used as the Reference [22]. The length of the π ‐spacer of the carbazole donor‐based organic dye with an oligothiophene π ‐spacer with carboxylic acid as acceptor was increased by adding thiophene units.…”

Theoretical Study of the Effect of Different π Bridges Including an Azomethine Group in Triphenylamine-Based Dye for Dye-Sensitized Solar Cells

“…Regarding D-π-A structure, several studies about dyes have been reported using different proposals. For example, modifying the donor part using coumarin [7,8], carbazole [9,10], phenothiazine [11,12], and triphenylamine [13,14]; modifying the acceptor part using cyanoacrylic acid [15] and alkoxysilane [16,17]; and mainly modifying the π-bridge using thiophene [18,19,20], benzene [21,22], dioxythiophene [23], and benzothiadiazole [24,25], among many others. Hence, the study and the understanding of the performance of D-π-A metal-free organic dyes is very important.…”