Exploring the effect of different coumarin donors on the optical and photovoltaic properties of azo‐bridged push‐pull systems: A theoretical approach

Abstract

We report the theoretical modeling of various azo-bridged coumarin-purpurin systems. The effect of varying the donor (coumarin) part of this D-π-D-π-A system was analyzed in terms of opto-electronic and photovoltaic parameters such as HOMO, LUMO, HOMO-LUMO energy gap, λ max , light harvesting efficiency, charge injection efficiency, open voltage, reorganization energy by employing density functional theory as incorporated in Gaussian 03 set of codes. The dye-TiO 2 adsorbed systems were also studied using the same level of theory. It was found that just by varying the donor, although of same nature, there is a marked effect on the efficiency parameters of the dye sensitized solar cells based on such dyes. Also, the dye molecules were found to be good sensitizers for TiO 2 semiconductors. K E Y W O R D S DFT, DSSC, light harvesting efficiency, optoelectronic, photovoltaic parameters | INTRODUCTIONDue to the over exploitation of the natural resources coupled with the increasing levels of pollutions, there is immediate need to develop some alternative, clean resources of energy. In this regard, solar energy is the easily available and clean form of energy that can be well harnessed to meet our present as well as future energy demands. To convert this solar energy into usable forms we have some devices called photovoltaic solar devices and amongst them dye sensitized solar cells (DSSC) are better options, owing to their easy manufacture, cost effectiveness, and flexibility.With the advent of the DSSC technology the conversion of the solar energy to electricity became cheap than the traditional silicon-based photovoltaics. [1,2] Amongst DSSCs, those based on organic dye sensitizers have been found to be advantageous owing to their easy synthesis and low cost. The study of these organic metal free dye sensitizers for DSSCs are important as they have paved the way for designing DSSCs with better efficiencies in a cost effective manner. Organic dyes have exhibited higher conversion efficiencies up to 12.5% for carbazoles and indenoperylene electron-donor based dye sensitizers while as 12.8% efficiency has been achieved for triphenylamine-based dye using cobalt-based electrolyte system. [3,4] Amongst the organic sensitizers, those based on push-pull framework or donor-π-acceptor (D-π-A) form are worth mentioning These push-pull dye molecules are very promising due to their high molar extinction coefficient, cost effectiveness, and diversity. [5][6][7][8][9] Along with experimental studies, a number of theoretical researches have been carried out on various organic dyes. The theoretical studies have served as a tool for verifying the results found experimentally. As such, number of such studies has been carried out, such as those based on coumarins [10][11][12][13][14][15][16] and triphenylamine. [17][18][19][20] Theoretical studies by several researchers [15,[21][22][23][24][25] on NKX coumarin derivatives have been carried for understanding the relationship between the molecular properties of these dye sensitizers and the...

Photovoltaic properties of the flavonoid‐based photosensitizers: Molecular‐scale perspective on the natural dye solar cells

“…The light‐harvesting ability, LHE , of the dyes is evaluated by Equation : where f is the oscillator strength. Electron driving force, eV OC , of the studied pigments, is also evaluated according to Equation : …”

“…The first dye‐sensitized solar cell (DSSC) was improved by O'Regan and Grätzel . DSSCs are engaging due to their low‐cost synthesis, working capability under the light conditions, and tunable transparency …”

Insight into incident photon to current conversion efficiency in chlorophylls

“…[16] Some efficient push-pull systems, such as azo-bridged coumarin-purpurin based systems (CM1-CM7) were studied. [17] On the basis of the results, the substitution of the donor moiety (coumarin) and solvent affect the optoelectronic and photovoltaic properties of the D-π-D-π-A systems. Among these dyes, CM6 was preferred because of a proper band gap, polarizability, spectroscopic behavior and light-harvesting efficiency.…”

“…Moreover, the interaction of the dyes with (TiO 2 ) 6 showed that these dyes are efficient photosensitizers for DSSCs. [17] The influences of the chemical structure of the sensitizers on the photovoltaic properties were investigated. [17][18][19][20] For example, polypyridyl dyes based on Cr 2+ and V 3+ show better performance in comparison with ruthenium-and other scarce metal-based polypyridyl dyes due to the moderate LHE , high efficiencies of electron and hole injection, which make them promising alternatives to scarce Ru 2+ metal ion.…”

“…[17] The influences of the chemical structure of the sensitizers on the photovoltaic properties were investigated. [17][18][19][20] For example, polypyridyl dyes based on Cr 2+ and V 3+ show better performance in comparison with ruthenium-and other scarce metal-based polypyridyl dyes due to the moderate LHE , high efficiencies of electron and hole injection, which make them promising alternatives to scarce Ru 2+ metal ion. [18] Also, theoretical insights into the effect of polycyclic aromatic hydrocarbons (PAHs) on monascus pigments (MPs) and as a photosensitizer for solar cells showed that the presentence of the PAHs reduces the electronic band gap and the electron injection efficiency of MPS.…”