Optoelectronic Properties of Triphenylamine Based Dyes for Solar Cell Applications. A DFT Study

Abstract

Dye-sensitized solar cells (DSSCs) based on triphenylamine (TPA) as a donor group linked with the acceptor cyanoacrylic acid electron acceptor by 2,2'-bithiophene as π-bridged (D-π-A) has been investigated by Density Functional Theory (DFT) at the B3LYP/6-311G(d,p) level of theory, to establish the conformational orientation of cyanoacrylic acid group as well as evaluate the effect of planarizing the 2,2'-bithiophene unit in position 3 and 3' by electron withdrawing or donor groups on the electronic structure properties of ground and doping(n,p) states. Also, the Time Dependent Density Functional Theory (TD-DFT) at the CPCM-TD-CAM-B3LYP//CAM-B3LYP/6-311G(d,p) level of theory were selected to modulate the electronic absorption spectra and charge-transfer capabilities of the molecules analyzed in the present work. The results indicate that adding an auxiliary donor or withdrawing group to the 2,2'-bithiophene in the (D-π-A) arrangement allow to modify the LUMO's energy of the dyes, while the HOMO´s energy is slightly affected.

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

“…[ 59 ] Likewise, the changes in the energy of the LUMO level are noted, but very negligible changes for Hybrid‐B3LYP are observed for both HOMO and LUMO. [ 59–61 ]…”

“…The decrease in the value of the band gap of D2 upon addition of the electron‐withdrawing oxadiazole group is due to lowering of its LUMO level. [ 60 ] A slight increase in band gap occurs when the π ‐bridge length was increased for D2A.…”

“…The HOMO of D3 is found to be −5.0, −5.6 eV, [ 60 ] and −5.1 eV and LUMO to be −4.2, −3.5 eV, [ 60 ] and −3.9 eV, with a band gap of −0.8, −2.1, and −1.2 eV when calculated using the respective functionals. On the other hand, in the case of D3A, the HOMO level is found to be −5.0, −5.6, and −5.1 eV and LUMO level to be −4.1, −3.5, and −3.9 eV, with band gaps of −0.9, −2.1, and −1.3 eV when calculated using GGA‐PBE, Hybrid‐B3LYP, and SCC‐DFTB, respectively.…”

“…A decrease in the value of band gap is observed on addition of the electron‐withdrawing oxadiazole in D3, whereas a slight increase in band gap occurs when the π ‐bridge length increases for D3A. [ 60 ] The extension in the length of the bridge enhances the light‐harvesting features of organic dyes but causes a reduction in the dye‐grafting ability to load on titanium, changes in molecular energy levels, charge displacement, and distribution, as well as photochemical properties. Gao et al have reported a reduction in open‐circuit voltage and efficiency for the longest π ‐bridge dye among a series of organic photosensitizers.…”

“…[59] Likewise, the changes in the energy of the LUMO level are noted, but very negligible changes for Hybrid-B3LYP are observed for both HOMO and LUMO. [59][60][61] 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.…”