Conduction Band Edge Of TiO2 Research Articles

Improved efficiency and stability for acridine orange sensitizers by adding electron donating/accepting π-linker moieties

Shortcomings associated with metal-free dye-sensitized solar cells can be overcome with dye modification. Using Density Functional Theory (DFT) and Time Dependent (TD-DFT), acridine orange dyes (main Donors) are modified with molecular moieties (2-Hydroxy-4-propoxyphen)(phenyl)methanone (UV absorber), 4,4′-Dimethoxydiphenylamine (Donor 1), 2-(Thiophen-2-yl)-1,3,4-oxadiazole (π-bridge), anisole (Donor 2), cyanoacetic-acid and carboxylic-acid functional groups (Acceptors 1 and 2), to form new UV Absorber-D-(A)2 and D’- π -D-(A)2 dyes with least computational costs, where acridine derivatives act as main donors. Absorption spectra, highest-occupied molecular orbitals, and lowest-unoccupied molecular orbitals are predicted by DFT and TD-DFT calculations. Ionization potential, electron affinity, electronegativity and light-harvesting efficiency are predicted with frontier-molecular orbital energies by Koopmans' theorem, using TiO2 conduction-band edge (ECB −4.0 eV) and [I-/I3-] redox-potential (-4.80 eV). Absorption redshifts with expanded range of 700 nm, and improved energy-alignment with TiO2, charge-transfer processes, redox-couple compatibility, cell stability and higher performance are all achieved by molecular level tuning of dyes.

Theoretical Investigations of Dye-Sensitized Solar Cells

This presentation considers theoretical investigations of dye-sensitized solar cells (DSSC). Theoretical methods were applied to investigate the interactions between titanium dioxide nanoparticles and sensitizers. The ONIOM model was used to obtain the geometries of different conformers of dye molecules with TiO2 and their binding energies. TD-DFT calculations were carried out to obtain the absorption spectra and the relative orbital energy levels of sensitizers and TiO2. The electronic couplings between different sensitizers and TiO2 were calculated using the fragment charge difference method. The redox potentials of the sensitizers are calculated to complete the full working cycle of a DSSC. We observed that the -COOH group is not the only possible binding site, and the sensitizers are more likely to be adsorbed horizontally on the TiO2 surface instead of being perpendicular to the surface having the -COOH group as a linker. The TiO2 nanoparticle was found to have minor influence on the absorptions of the sensitizers with the spectra shift smaller than 0.2 eV. TiO2 has more influence on the absorptions of softer and larger molecules because the interactions between sensitizers and TiO2 twist the conjugated chromophore structures. Compared to the neutral form, the deprotonated anion conformers of the sensitizers have larger binding energy and lower LUMO level against conduction band of TiO2. The gap between the LUMO of sensitizers and conduction band edge of TiO2 might indicate the coupling strength between the sensitizers and TiO2. Several binding groups have shown promising properties for interacting with the TiO2 nanoparticle and generally deprotonated anion forms of the dyes were strongly bonded to the TiO2 nanoparticle. The model and associated calculated results provide close agreement with experimental data and give crucial atomistic information of the relevant processes in dye-sensitized solar cells.

Designing of PC31BM‐based acceptors for dye‐sensitized solar cell

AbstractThree push‐pull dyes with triphenylamine as donor, thiophene as spacer and fullerene‐based acceptors have been designed using density functional theory (DFT) for dye‐sensitized solar cells (DSSCs). Here, we have done a systematic case study by varying the acceptor of dye. PCBM type of acceptors are chosen. However, the main focus lies on the fact that fullerene C60, which is used as conventional fullerene in PCBM, is replaced by C30. Further, two more structures are derived, where C30 is changed by two of its doped counterparts, C10B10N10 and C10B10P10. Structural integrity of these dyes is checked and found to be stable. Their electronic properties also provide a good insight into their characteristics. Highest occupied molecular orbital (HOMO) energy level of the dyes is positioned under the redox potential of redox couple, , which means that the dyes can be regenerated. LUMO energy value of dyes with C30 and C10B10N10 lies above the conduction band of semiconductor, TiO2, and hence electrons from the excited state of the dyes can be injected into the conduction band edge of TiO2. For C10B10P10, lowest unoccupied molecular orbital (LUMO) lies slightly below the conduction band of TiO2 (for B3LYP functional). Therefore, few more configurations of C10B10P10 have been checked by replacing B and P atoms with C atoms. Notably, incorporation of solvent rules out this exception and all the dyes become eligible for electron regeneration also. Time‐dependent DFT (TDDFT) studies throw light on their photochemical properties, which is one of the interim criteria for any system getting selected as a dye in the DSSCs.

Carminic acid extracted from cochineal insect as photosensitizer for dye‐sensitized solar cells

In an attempt to investigate influence of the utilization of organic dyes on photovoltaic performance of low-cost dye-sensitized solar cells (DSSCs), carminic acid (CA) obtained from cochineal insect was employed as photosensitizer to fabricate DSSCs. To recognize light absorption behavior of the CA, UV-Vis spectroscopy was taken. The CA comprises noticeable spectrum of solar radiation, 430 to 540 nm that makes it appropriate for use as a photosensitizer in DSSCs. Fourier transform infrared (FTIR) spectra of the CA revealed the presence of carboxylic functionality, enabling good anchorage to the surface of TiO2. The electrochemical impedance spectroscopy (EIS) analysis manifests that the suppression of the electron recombination at the TiO2/CA/electrolyte interface was insufficient. Quantum chemical calculations of the CA dye were performed by using the density functional theory (DFT). The lowest unoccupied molecular orbital (LUMO) level of the CA matched well for the injection of electron from the CA to the conduction band edge of TiO2. The achieved photo-conversion efficiency of a DSSC employing the CA photosensitizer was 1%, which was found to be much higher than that of several natural dyes-based DSSCs under a simulated solar light illumination of 100 mW/cm2.

Acceptor substituent effect on triphenylamine-based organic dye sensitizers for DSSCs: quantum chemical study

In this work, a series of triphenylamine (TPA)- based dye molecules (A1–A5) for dye-sensitized solar cells (DSSCs) application has been designed and screened. The electron donor contains TPA, thieno[3,2-b]thiophene, as the π-bridge, cyanoacrylic acid as electron acceptor based on donor–π-spacer–acceptor (D-π-A) as reference dye (3a). In order to enhance the tuning, effect of acceptor moieties was investigated at 3a dye. The electron acceptor effect of the substituent on the absorption spectra and photovoltaic (PV) properties has been investigated by the combination of density functional theory (DFT) and time-dependent DFT (TD-DFT) method approaches. Different exchange-correlation (XC) functionals were initially evaluated in order to establish a proper methodology for calculating the excited state energy of the 3a dye. Consequently, TD-ωB97XD method and 6-31G(d) basis set have used the comparison of experimental value. From the calculated results, it was concluded that the A4 (PO3H2) and A5 (SO2H) dyes are strongly grouped for more red-shift and electrons injected into semiconductor the conduction band edge of TiO2 was successful. It is expected that our research will pave a new method to design efficient organic D-π-A dye sensitizers in DSSCs.

Synthesis, characterization, and theoretical studies of the photovoltaic properties of novel reactive azonitrobenzaldehyde derivatives.

All dyes conduct but at different degrees of absorption; it is interesting to study the degree of conductivity and absorptivity of novel reactive azo-dyes in respect to dye-sensitized solar cells (DSSCs) to ascertain their viability for such applications. In this study, four novel reactive azo-dyes were experimentally synthesized from p-aminobenzaldehyde, 4-amino-3-nitrobenzaldehyde, and aniline through series of condensation and coupling reactions. The various functional groups, molecular connectivities, and molecular weight of the various fragments of the synthesized dyes were elucidated using the GC-MS, FT-IR, UV-vis, and NMR respectively. The experimentally determined structures were modeled and investigated using density functional theory (DFT) and time-dependent density functional theory (TD-DFT) approaches to computationally compute the electronic structure properties, reactivity, absorption and solvatochromism in four different phases: gas, ethanol, acetone, and water, and the photovoltaic properties for possible applications in dye-sensitized solar cells (DSSCs). By comparing the HOMO (EH) and the LUMO (EL) energies from the results obtained demonstrates that dye D has the highest EL energy value of −2.48 eV with a relatively lowest EH energy value of −5.63 eV such that it lies underneath the conduction band edge of TiO2 which is necessary to enable charge regeneration. Pi-electron delocalization was observed from the natural bond orbital (NBO) calculations between the different aromatic rings with dye B and A having the relatively highest and least second-order stabilization energies between σ* → σ* and LP* → LP interacting orbitals respectively. It is also observed in all the solvents that the Gibbs free energy of injection (ΔGinject) is greater than 0.2 eV and hence, all the studied azo structures in the four phases provided efficient electron injection and light harvesting efficiency (LHE), however, the value of ΔGinject for dyes B and D is greatest in all the four phases and thus, provided the highest electron injection of all the dyes. From the fact-findings of quantum theory of atoms-in-molecules (QTAIM), dyes A and C have extra-stability due to their relatively high numbers of intramolecular H-bond interactions along with some additional intra-atomic bonding between atoms within the studied compounds. Hence, all the four dyes are good for DSSCs applications.

A DFT/TD-DFT study on the possible replacement of Ru(II) with Fe(II) in phthalocyanine-based dye-sensitized solar cells

Density functional theory and time-dependent density functional theory (DFT/TD-DFT) methods have been used to study the photo-voltaic and photophysicochemical properties of some metal-free and metal-containing phthalocyanine (Pc) derivatives (1–12) for application in dye-sensitized solar cells (DSSCs). The TD-DFT and molecular ground-state data were used to estimate the relative position of the TiO2 conduction band edge to the lowest unoccupied molecular orbital (LUMO) position (δp). The diffusion coefficients (Dπ), and oscillator strengths (f) at maximum absorption wavelengths of the molecules in the visible or near-infrared (near-IR) region were also estimated. Fluorescence emission (ϕf) and charge collection (ηc) efficiencies obtained using the method reported recently by our group were used in estimating the dyes’ incident photon conversion efficiency (IPCE). The estimated parameters have been used to characterize the dyes and evaluate their suitability for application in photo-voltaic technology both in gas phase and in acetonitrile. The overall results showed that iron(II) could be a possible substitute for ruthenium ion, as the choice metal ion for phthalocyanine-based DSSCs.

Effects of structure and electronic properties of D-π-A organic dyes on photovoltaic performance of dye-sensitized solar cells

Abstract Herein, we examine the performance of dye-sensitized solar cells containing five D-π-A organic dyes designed by systematic modification of π-bridge size and geometric structure. Each dye has a simple push-pull structure with a triarylamino group as an electron donor, bithiophene-4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M11), 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene-thiophene (M12), thiophene-4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M13), 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene-benzene (M14), and 4,4-dimethyl-4H-cyclopenta[1,2-b:5,4-b’]dithiophene (M15) units as π-bridges, and cyanoacrylic acid as an electron acceptor/anchor. The extension of the π-bridge linkage favors wide-range absorption but, because of the concomitant molecular volume increase, hinders the efficient adsorption of dyes on the TiO2 film surface. Hence, higher loadings are achieved for smaller dye molecules, resulting in (i) a shift of the TiO2 conduction band edge to more negative values, (ii) a greater photocurrent, and (iii) suppressed charge recombination between the photoanode and the redox couple in the electrolyte. Consequently, under one-sun equivalent illumination (AM 1.5 G, 100 mW/cm2), the highest photovoltage, photocurrent, and conversion efficiency (η = 7.19%) are observed for M15, which has the smallest molecular volume among M series dyes.

Enhanced Power Conversion Efficiency of Dye-Sensitized Solar Cells by Band Edge Shift of TiO2 Photoanode.

By simple soaking titanium dioxide (TiO2) films in an aqueous Na2S solution, we could prepare surface-modified photoanodes for application to dye-sensitized solar cells (DSSCs). An improvement in both the open-circuit voltage (Voc) and the fill factor (FF) was observed in the DSSC with the 5 min-soaked photoanode, compared with those of the control cell without any modification. The UV–visible absorbance spectra, UPS valence band spectra, and dark current measurements revealed that the Na2S modification led to the formation of anions on the TiO2 surface, and thereby shifted the conduction band edge of TiO2 in the negative (upward) direction, inducing an increase of 29 mV in the Voc. It was also found that the increased FF value in the surface-treated device was attributed to an elevation in the shunt resistance.

Re-evaluating the role of phosphinic acid (DINHOP) adsorption at the photoanode surface in the performance of dye-sensitized solar cells.

Dineohexyl phosphinic acid (DINHOP) is a popular amphiphilic molecular insulator considered as the most efficient co-adsorbent (co-grafter) for the improvement of the photovoltaic performance of TiO2 based hybrid solar cells. Although the effect of its incorporation on the improvement of cell performance has been well demonstrated, the mechanisms through which it affects the photovoltaic and electrodynamic parameters of the cells are not yet clear. Here we re-examine the mechanism through which the DINHOP co-adsorbent affects the photovoltaic and electrodynamic parameters of dye-sensitized solar cells. Although DINHOP is widely believed to inhibit (passivate) recombination across the TiO2/electrolyte interface, we demonstrate that this is sublte, noticeable only for a very high concentration (e.g. 750 μM) of DINHOP, co-sensitized with a dye. For the most frequently used DINHOP concentrations (e.g. 75 μM and 375 μM), an observed increase of the diffusion coefficient and recombination rate could be directly associated with a decrease of total intra-gap states in TiO2. For a DINHOP concentration as low as 75 μM, the conduction band edge of TiO2 moves upward due to the combined effect of charge accumulation and a decrease in the total number of intra-gap states leading to an effective enhancement of the DCCS VOC, where the decrease in total intra-gap states does not contribute positively. The decrease of total intra-gap states enhances both the transport and recombination rates of charge carriers by the same fraction due to a transport-limited recombination process. On the other hand, adsorption of DINHOP molecules at higher concentrations such as 375 μM and 750 μM additionally modifies the distribution of intra-gap states, affecting the nonlinear recombination parameter of charge carriers at the anode-electrolyte interface, leading to an overall enhancement of the DSSC VOC. In all cases, incorporation of DINHOP results in an overall improvement of the solar cell efficiency (∼14% compared with the reference one), with a maximum for a concentration of 375 μM, where no inhibition of recombination was observed. Interestingly, for this DINHOP concentration, we estimate that 1 DINHOP molecule per every 12 molecules of dye occupies the intra-gap states of the TiO2 surface. The results presented in this work elucidate the physical phenomena involved in the interaction of co-adsorbents, pre-treatments or additives with the electrolyte at the surface of the TiO2 photoanode of dye-sensitized solar cells and can be easily adapted to study other electrochemical systems.

Charge Transfer in c-Si(n++)/TiO2(ALD) at the Amorphous/Anatase Transition: A Transient Surface Photovoltage Spectroscopy Study.

Electronic properties and charge transfer processes were studied in an n-Si(n++)/TiO2(ALD) system at an amorphous TiO2/anatase transition by transient surface photovoltage spectroscopy at constant photon flux. The TiO2 layers were deposited by atomic layer deposition (ALD) onto highly doped silicon (c-Si(n++)), and the phase composition of the TiO2 layers changed with increasing thickness from amorphous to the anatase polymorph as anatase crystallites started to grow at the surface. Depending on phase composition, the band gap of TiO2 correlated with the characteristic energy of exponential tails. In most cases, photogenerated electrons were separated toward the back contact. For photogeneration in c-Si(n++), electron back transfer was limited by Auger recombination with holes in the surface space charge region of c-Si(n++), and by electron transfer across the interface, either via exponentially distributed states near the conduction band edge of amorphous TiO2 or via distance-dependent recombination with holes trapped in anatase. For photogeneration in TiO2, electron back transfer was limited by trapping in TiO2. Under strong light absorption in amorphous TiO2 with anatase crystallites on top, electrons were preferentially separated toward the TiO2 surface.

Short-term light soaking effect on dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) are one of the most promising third generation solar cells and have been regarded as a competitive alternative to the conventional silicon-based photovoltaic devices due to their relatively low production cost. Light soaking effect is an intriguing phenomenon that exists in DSSCs, which refers to the enhancement of the electrical parameters in the cells after being exposed to light soaking. In this paper, we report on the variation in the electrical parameters of DSSCs under continuous exposure to a simulated solar irradiation for a period up to 6h. Increments of Jsc and Voc in DSSC were observed after 6h of light soaking, which led to improved efficiency from 3.87% to 4.50%. The improvements may be ascribed to the formation of electron trapping states below the TiO2 conduction band edge, which facilitated the charge carrier transport.

Enhanced Interfacial Binding and Electron Extraction Using Boron-Doped TiO2 for Highly Efficient Hysteresis-Free Perovskite Solar Cells.

Perovskite solar cells (PSCs) have witnessed astonishing improvement in power conversion efficiency (PCE), more recently, with advances in long‐term stability and scalable fabrication. However, the presence of an anomalous hysteresis behavior in the current density–voltage characteristic of these devices remains a key obstacle on the road to commercialization. Herein, sol–gel‐processed mesoporous boron‐doped TiO2 (B‐TiO2) is demonstrated as an improved electron transport layer (ETL) for PSCs for the reduction of hysteresis. The incorporation of boron dopant in TiO2 ETL not only reduces the hysteresis behavior but also improves PCE of the perovskite device. The simultaneous improvements are mainly ascribed to the following two reasons. First, the substitution of under‐coordinated titanium atom by boron species effectively passivates oxygen vacancy defects in the TiO2 ETL, leading to increased electron mobility and conductivity, thereby greatly facilitating electron transport. Second, the boron dopant upshifts the conduction band edge of TiO2, resulting in more efficient electron extraction with suppressed charge recombination. Consequently, a methylammonium lead iodide (MAPbI3) photovoltaic device based on B‐TiO2 ETL achieves a higher efficiency of 20.51% than the 19.06% of the pure TiO2 ETL based device, and the hysteresis is reduced from 0.13% to 0.01% with the B‐TiO2 based device showing negligible hysteresis behavior.

Theoretical design of porphyrin dyes with electron-deficit heterocycles towards near-IR light sensitization in dye-sensitized solar cells

We develop a series of porphyrin sensitizers with electron-deficit heterocycles based on the well-known YD2-o-C8 dye for application in dye-sensitized solar cells with the help of ab initio density functional theory calculations and quantum dynamics simulation based on the tight-binding extended Hückel Hamiltonian at the semiempirical level. The calculation results show that introduction of electron-deficit heterocycles into the porphyrin dyes can remarkably red-shift and broaden the Q band of the absorption spectrum and extend the coverage into near-infrared region, improving the light-harvesting ability. The key parameters influencing the photocurrent and photovoltage performance such as maximum short-circuit photocurrent (JSCmax), intramolecular charge transfer, interface electron injection, and the shift of TiO2 conduction band edge (ΔECB) are superior to YD2-o-C8 dye. Therefore, the designed sensitizers would be promising candidate for utilization in dye-sensitized solar cells.

Interface Electrostatics of Solid-State Dye-Sensitized Solar Cells: A Joint Drift-Diffusion and Density Functional Theory Study

Dye-sensitized solar cells (DSCs) have gained great attention in recent years due to their low-cost fabrication, flexibility and high power conversion efficiency. In a DSC, due to interfaces between the dye and the charge transport materials, the interface electrostatics becomes a key factor determining the overall performance of the cell. Liquid electrolyte based DSCs suffer low stability, electrolyte leakage and in some cases electrode corrosion. Replacing liquid electrolyte with a solid semiconducting material leads to poor interfacial contacts, hence the interface electrostatics becomes one of the limiting factors. In this work, we present a drift-diffusion (DD) and density functional theory (DFT) study of solid-state DSCs to investigate the electrostatics at the TiO2/organic dye/Spiro OMeTAD interface, and its impact to the adsorbed dye energy levels, its absorption spectrum and the related charge injection. In our 3D drift-diffusion model, we solve a set of drift-diffusion equations coupled to Poisson equation for electrons, holes, doping impurities and the interface traps simultaneously. After that, we use first principles DFT modeling of dye-sensitized interfaces in the presence of the calculated electric fields. We find that interface traps located below the conduction band edge of mesoporous TiO2 influence the accumulation of photogenerated holes and built-in electric field near the interface. The built-in electric field leads to change the energetics at the dye/TiO2 interface leading to poor charge injection from excited dye into the TiO2. The simulations were carried out for different electronic trap density in TiO2 and different doping levels in the Spiro OMeTAD hole transport layer. This study helps to a better understanding of interface electrostatics and its role in the charge injection mechanism of solid-state DSCs.

A promising heat-induced supramolecular metallogel electrolyte for quasi-solid-state dye-sensitized solar cells

A series of Fe(III)-based coordination-driven metallogel (MOG) electrolytes are obtained by absorbing liquid electrolytes with MOGs and applied to quasi-solid-state dye-sensitized solar cells (DSSCs). The MOG, prepared by Fe3+ and trimesic acid, presents a porous and flower-like structure, which can ensure the effective diffusion of I−/I3− ions and excellent infiltration to the TiO2 photoanode. Moreover, the mechanical property of MOG is stable enough to guarantee the photovoltaic performances of DSSCs in the operating environment. In the MOG electrolyte, trimesic acid acts as the gelator to coordinate with Fe3+ to form MOG. Furthermore, the condition of TiO2 conduction band edge of quasi-solid-state DSSC shifts with the liquid electrolyte concentration increasing in MOG, which results in both Voc and Jsc increasing firstly and then decreasing, and the process of electron kinetics is investigated to illustrate these differences. Finally, an excellent photoelectric conversion efficiency of 5.31% is obtained for MOG electrolyte–based quasi-solid-state DSSC.

Performance Regulation of Thieno[3,2-b]benzothiophene π-Spacer-Based D-π-A Organic Dyes for Dye-Sensitized Solar Cell Applications: Insights From Computational Study.

Dye-sensitized solar cells (DSSCs) have been widely investigated; however, the development of promising dye sensitizers is still appealing. In this work, we perform a detailed theoretical search for high-efficiency D-π-A organic dyes using density functional theory and time-dependent density functional theory calculations. Specifically, we perform geometric optimization, and electronic structure and absorption spectra calculations for isolated dyes for two thieno[3,2-b]benzothiophene π-spacer-based D-π-A organic dyes SGT129 and SGT130, which show significant efficiency difference, before and after binding to a TiO2 semiconductor. The calculation results reveal that the coplanar configuration between the electron donor and the π-spacer can enhance electronic communication efficiently, thus facilitating intra-molecular charge transfer from the electron donor to the acceptor groups in SGT130. The absorption spectrum of SGT130 broadens and is red-shifted owing to the decreased bandgap. The higher light-harvesting efficiency, favorable intra-molecular charge transfer, larger shift of the conduction band edge in the TiO2 semiconductor, and slower charge recombination between the injected electrons in the TiO2 conduction band and the electrolyte explain the superior efficiency of SGT130 over that of SGT129. Using SGT130 as the reference dye, we further design four novel dyes 1–4 by modifying the π-spacer with electron-rich and electron-withdrawing moieties. Judging from the theoretical parameters influencing the short-circuit current and open-circuit voltage, we found that all dyes would perform better than SGT130 in terms of the favorable interfacial charge transfer (ICT) and light-harvesting efficiency, as well as the larger shift of the TiO2 conduction band edge. Our theoretical research is expected to provide valuable insights into the molecular modification of TBT-based D-π-A organic dyes for DSSC applications.

Natural pigments in dye-sensitized solar cell (DSSC): a DFT-TDDFT study

The molecular structures and photophysical properties of twelve types of the dyes from natural pigments of chlorophyll, flavonoid, carotenoid and anthocyanin were calculated with density functional theory (DFT) and time-dependent DFT (TD-DFT). Based on the comparison and better agreement between experimental wavelengths of maximum absorption and their calculated values with functionals of B3LYP, CAM-B3LYP and BHand-H, the B3LYP/6-31G** level was chosen for the process of our studies. The dyes’ properties in solvent environment were carried out using conductor-like polarizable continuum model methods (CPCM-DFT and TD-CPCM-DFT). The results show that pigment type affects the photophysical properties, and the dyes of a specific pigment type have nearly the same properties. Anthocyanins have the highest values of ionization potential (IP), electron affinity (EA), electronic chemical potential (µ) (their absolute values), chemical hardness (η), electrophilicity index (ω), electroaccepting power (ω+) and electrodonating power (ω−), which can lead to high efficiency of these dyes type for dye-sensitized solar cells (DSSCs). Energy gap of ELUMO and EHOMO of the dyes respectively with the conduction band edge of TiO2 (ECB) and Eredox of $$\left(\tt {I^ - }/I_{3}^{ - }\right)$$ couple (ΔEL and ΔEH), the free energy difference for electron injection (ΔGinject) and the driving force for dye regeneration (ΔGreg), the maximum absorption wavelengths of peaks (λmax) and oscillator strength values (f) for all the dyes in gas, acetonitrile and water phases were calculated and explained. These parameters show that carotenoids, chlorophylls and anthocyanins are more appropriate pigments than flavonoid pigment and the estimated open-circuit photo-voltage values (eVoc) showed that flavonoids are the desirable pigment. We expect these results could be helpful for DSSC producers to choose highly efficient natural dyes according to their optical and electronic properties.

Highly improved photocurrent and stability of dye-sensitized solar cell through quasi-solid-state electrolyte formed by two low molecular mass organogelators

Abstract A well-organized quasi-solid-state electrolyte is formed by binary mixtures of bisamide and valine as co-gelator via intermolecular hydrogen bonds. It is interesting that the ratio of the two components of quasi-solid-state electrolyte can be tuned to shift the position of TiO2 conduction band edge, which can obviously enhance the driving force of electron injection process. Consequently, compared with the liquid electrolyte based dye-sensitized solar cell DSSC, the short-circuit current density (Jsc) of solar cellassembled by this quasi-solid-state electrolyte is increased about 12%. Moreover, the intensity-modulated photocurrent spectroscopy/intensity-modulated photovoltage spectroscopy (IMPS/IMVS) and electrochemical impedance spectroscopy (EIS) are carried out to investigate the influences of gelation on the kinetic processes of electron transport and recombination in DSSC. It is found that with the increasing of valine, the 3D network of quasi-solid-state electrolyte becomes looser and the electron transportation process is accelerated, meanwhile, the electron recombination lifetime is prolonged. As result, the quasi-solid-state solar cells (QS-DSSCs) employed with the bi-component quasi-solid-state electrolytes obtained a higher efficiency of 6.1% at AM 1.5 (100 mW cm2), but the efficiency of QS-DSSC based on the unitary component quasi-solid-state electrolyte formed by bisamide is only 5.3%. More importantly, these QS-DSSCs exhibit more excellent photo-thermal stability than the liquid electrolyte based DSSC.

Position of the anchoring group determined the sensitization efficiency of metal-free D-π-A dyes: Combined experimental and TD–DFT insights

We report on the design and synthesis of new D-π-A organic sensitizers incorporating D35 as the electron donor unit and (benzyloxy)benzene as the π- linker. The structure and yield of the synthesized dyes were confirmed via The 1H NMR, 13C NMR, and mass spectrometry analyses. The density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations were used to get insights on the electronic properties of the synthesized dyes, indicating their capability as photosensitizers. The photophysical characteristics, electrochemical properties, and photovoltaic performance of the sensitizers were investigated. The cyclic voltammetry measurements showed that the oxidation potentials of the excited states of the dyes are more negative than the conduction band edge of anatase TiO2 and their ground state oxidation potentials are more positive than the CoII/III redox shuttle, indicating their potential as photosensitizers. The dye containing benzyloxy group at the para position to the anchoring group showed higher power conversion efficiency (PCE), higher light harvesting efficiency (LHE), wider range of absorption, lower bandgap, higher incident photon-to-current conversion efficiency (IPCE), and higher excitation binding energy than the counterpart dye containing benzyloxy group in the ortho position.