Dye-sensitized Devices Research Articles

Ligand-Solvent Coordination Enables Comprehensive Trap Passivation for Efficient Near-Infrared Quantum Dot Light-Emitting Diodes.

Near-infrared light-emitting diodes (NIR LEDs) based on perovskite quantum dots (QDs) have produced external quantum efficiency (EQE) of ~15 %. However, these high-performance NIR-QLEDs suffer from immediate carrier quenching because of the accumulation of migratable ions at the surface of the QDs. These uncoordinated ions and carriers-if not bound to the nanocrystal surface-serve as centers for exciton quenching and device degradation. In this work, we overcome this issue and fabricate high-performance NIR QLEDs by devising a ligand anchoring strategy, which entails dissolving the strong-binding ligand (Guanidine Hydroiodide, GAI) in the mediate-polar solvent. By employing the dye-sensitized device structure (phosphorescent indicator), we demonstrate the elimination of the interface defects. The treated QDs films exhibit an exciton binding energy of 117 meV: this represents a 1.5-fold increase compared to that of the control (74 meV). We report, as a result, the NIR QLEDs with an EQE of 21 % which is a record among NIR perovskite QLEDs. These QLEDs also exhibit a 7-fold higher operational stability than that of the best previously reported NIR QLEDs. Furthermore, we demonstrate that the QDs are compatible with large-area QLEDs: we showcase 900 mm2 QLEDs with EQE approaching 20 %.

Recent Advances in Graphene-Enabled Materials for Photovoltaic Applications: A Comprehensive Review.

Graphene's two-dimensional structural arrangement has sparked a revolutionary transformation in the domain of conductive transparent devices, presenting a unique opportunity in the renewable energy sector. This comprehensive Review critically evaluates the most recent advances in graphene production and its employment in solar cells, focusing on dye-sensitized, organic, and perovskite devices for bulk heterojunction (BHJ) designs. This comprehensive investigation discovered the following captivating results: graphene integration resulted in a notable 20.3% improvement in energy conversion rates in graphene-perovskite photovoltaic cells. In comparison, BHJ cells saw a laudable 10% boost. Notably, graphene's 2D internal architecture emerges as a protector for photovoltaic devices, guaranteeing long-term stability against various environmental challenges. It acts as a transportation facilitator and charge extractor to the electrodes in photovoltaic cells. Additionally, this Review investigates current research highlighting the role of graphene derivatives and their products in solar PV systems, illuminating the way forward. The study elaborates on the complexities, challenges, and promising prospects underlying the use of graphene, revealing its reflective implications for the future of solar photovoltaic applications.

Increased solar-driven chemical transformations through surface-induced benzoperylene aggregation in dye-sensitized photoanodes

The impact of benzo[ghi]perylenetriimide (BPTI) dye aggregation on the performance of photoelectrochemical devices was explored, through imide-substitution with either alkyl (BPTI-A, 2-ethylpropyl) or bulky aryl (BPTI-B, 2,6-diisopropylphenyl) moieties, to, respectively, enable or suppress aggregation. While both dyes demonstrated similar monomeric optoelectronic properties in solution, adsorption onto mesoporous SnO2 revealed different behavior, with BPTI-A forming aggregates via π-stacking and BPTI-B demonstrating reduced aggregation in the solid state. BPTI photoanodes were tested in dye-sensitized solar cells (DSSCs) before application to dye-sensitized photoelectrochemical cells (DSPECs) for Br2 production (a strong oxidant) coupled to H2 generation (a solar fuel). BPTI-A demonstrated a twofold higher dye loading of the SnO2 surface than BPTI-B, resulting in a fivefold enhancement to both photocurrent and Br2 production. The enhanced output of the photoelectrochemical systems (with respect to dye loading) was attributed to both J- and H- aggregation phenomena in BPTI-A photoanodes that lead to improved light harvesting. Our investigation provides a strategy to exploit self-assembly via aggregation to improve molecular light-harvesting and charge separation properties that can be directly applied to dye-sensitized photoelectrochemical devices.Graphical Increased Solar-Driven Chemical Transformations through Surface-Induced Benzoperylene Aggregation in Dye-Sensitized Photoanodes. Benzo[ghi]perylenetriimide (BPTI) dyes are investigated to reveal the effect of aggregation by π-stacking on photovoltaic parameters in dye-sensitized devices. Photoanodes with aggregating BPTIs show both J- and H- aggregation phenomena leading to enlarged visible light absorbance and increased electron injection. The use of aggregating BPTI outperforms a non-aggregation BPTI with fivefold in terms of photocurrent and product generation.

Visible-Light-Active Unsymmetrical Squaraine Dyes with Pyridyl Anchoring Groups for Dye-Sensitized Solar Cells.

Visible-light-active alkyl group-wrapped unsymmetrical squaraine dyes SD1-SD3 were synthesized, featuring an indoline donor and pyridine and carboxylic acid anchoring groups. Their photophysical, electrochemical, and photovoltaic characteristics were examined by fabricating a dye-sensitized solar cell (DSSC) device. Both carboxylic acid and pyridine anchoring groups containing squaraine dyes SD3 and SD2 possess similar photophysical and electrochemical characteristics. However, their photovoltaic performances were completely different. The SD3 dye with the carboxylic acid anchoring group displayed a DSSC device efficiency of 7.20% (VOC 0.81 V; JSC 12.29 mA/cm2) using iodolyte (I-/I3-) electrolyte, compared to SD1 (VOC 0.659 V; JSC 4.97 mA/cm2; and η - 2.34%) and SD2 (VOC 0.629 V; JSC 1.68 mA/cm2; and η - 0.84%), which were featured with pyridyl anchoring groups. These results were attributed to dye loading on the Lewis and Brønsted acidic sites of TiO2 and the importance of aggregated structures for photocurrent generation. In the incident photon-to-current efficiency (IPCE) analysis, SD1 dye-sensitized devices exhibited photocurrent generation from both monomeric and aggregated dyes on the TiO2 surface. In contrast, SD2 showed photocurrent generation solely from aggregated states. Despite the introduction of long alkyl chains to reduce dye aggregation and charge recombination, the results indicated preferential charge injection from only the aggregated SD2 dye on TiO2. Fluorescence-quenching experiments indicated an efficient charge transfer from the aggregated SD2 dye to TiO2 compared to that of the monomeric dye. Cosensitization, a method to enhance the light-harvesting efficiency and photocurrent generation in DSSCs, was explored by simultaneously cosensitizing pyridyl-based dyes (SD1 and SD2) with a blue-colored carboxylic acid-based squaraine dye SD4. IPCE analysis demonstrated that both SD1 and SD4 contributed to generating a photocurrent of 9.11 mA/cm2. The sequential cosensitization of SD1 and SD4 with the coadsorbent CDCA showed the highest performance, with a VOC of 0.663 V, a JSC of 11.43 mA/cm2, and an efficiency (η) of 5.20%.

Perovskite- and Dye-Sensitized Solar-Cell Device Databases Auto-generated Using ChemDataExtractor

The number of scientific publications reporting cutting-edge third-generation photovoltaic devices is increasing rapidly, owing to the pressing need to develop renewable-energy technologies that address the climate-change crisis. Consequently, the field could benefit from a central repository where photovoltaic-performance metrics, such as the power-conversion efficiency (η) are recorded. We present two automatically generated databases that contain photovoltaic properties and device material data for dye-sensitized solar cells (DSCs) and perovskite solar cells (PSCs), totalling 660,881 data entries representing 57,678 photovoltaic devices. The databases were generated by applying the text-mining toolkit ChemDataExtractor on a corpus of 25,720 articles. A multi-faceted evaluation, incorporating manual and automatic methods, was applied to ensure that the data contained therein were of the highest quality, with precision metrics ranging from 73.1% to 95.8%. The DSC database contains 475,045 entries representing 41,680 devices, and the PSC database contains 185,836 entries representing 15,818 devices. The databases are available in MongoDB and JSON formats, which can be queried in Python, R, Java and MATLAB for data-driven photovoltaic materials discovery.

Inhibited interlayer electron transfer in metal ion linked multilayers on mesoporous metal oxide films

The incorporation of dye-electron donor motifs on metal oxide surfaces is a common strategy to increase dye regeneration rate, slow recombination, and improve overall dye-sensitized device performance. Here we used zinc ion linked multilayer assembly of a dye (N3) and a cobalt polypyridyl electron donor (Co) on TiO2 as an alternative to traditional covalently linked dye-donor systems. The formation of the TiO2-N3-Zn-Co multilayer was monitored using UV–Vis and ATR-IR and we introduced inductively coupled plasma mass spectrometry as a means of quantifying the surface loading of spectroscopically obscured molecules like Co. Interestingly, and contrary to the original intent, the addition of Co electron donor impeded the dye-sensitized device in nearly every performance metric. Transient absorption measurements indicate that both excited state quenching of N3 by Co and Co to N3+ electron transfer are slower than the intrinsic excited state decay and recombination, respectively. We suggest that the geometric restriction imposed by the metal ion linked architecture sufficiently slows electron transfer such that Co is effectively inert in this assembly. While this bilayer did not improve device performance, these insights may guide new design strategies that will improve performance and/or will be of use in other applications where electron transfer is not desired but say communication of spin and/or magnetic moment is needed.

Interfacial Electron Transfer in Dye-Sensitized TiO2 Devices for Solar Energy Conversion

The development of cost-effective molecular devices that efficiently capture and convert sunlight into other useful forms of energy is a promising approach to meet the world’s increasing energy demands. These devices are designed through a successful combination of materials and molecules that work synergistically to promote light-driven chemical reactions. Light absorption by a surface-bound chromophore triggers a sequence of interfacial electron transfer processes. The efficiencies of the devices are governed by the dynamic balance between the electron transfer reactions that promote energy conversion and undesirable side reactions. Therefore, it is necessary to understand and control these processes to optimize the design of the components of the devices and to achieve higher energy conversion efficiencies. In this context, this review discusses general aspects of interfacial electron transfer reactions in dye-sensitized TiO2 molecular devices for solar energy conversion. A theoretical background on the Marcus-Gerischer theory for interfacial electron transfer and theoretical models for electron transport within TiO2 films are provided. An overview of dye-sensitized solar cells (DSSCs) and dye-sensitized photoelectrosynthesis cells (DSPECs) is presented, and the electron transfer and transport processes that occur in both classes of devices are emphasized and detailed. Finally, the main spectroscopic, electrochemical and photoelectrochemical experimental techniques that are employed to elucidate the kinetics of the electron transfer reactions discussed in this review are presented.

Density functional theory design of double donor dyes and electron transfer on dye/TiO2(101) composite systems for dye-sensitized solar cells.

In this work, we designed a series of double donor organic dyes, named ME101–ME106, based on experimentally synthesized dye WD8, and further investigated their electronic structure, the stability of the dye/TiO2 (101) systems, density of states (DOS) and absorption spectra using density functional theory (DFT) and time-dependent DFT (TDDFT). The molar extinction coefficients of all designed dyes are higher than WD8. It's fascinating that ME106 exhibits a smallest energy gap and 75 nm redshifts compared to WD8. The results of calculations reveal that ME101–ME106/TiO2(101) surfaces are more stable than WD8, double donor dyes have sufficient electron injection driving force and have very strong transfer electron ability. It is expected that the design of double donors can provide a new understanding and guidance for the investigation of high efficiency dye-sensitized devices.

Photoinduced Electron Injection in a Fully Solvated Dye-Sensitized Photoanode: A Dynamical Semiempirical Study

Dye-sensitized solar cells and dye-sensitized photoelectrochemical cells have attracted much interest in recent years for solar energy conversion. More effort is still required to increase the efficiency of these devices, which is closely linked to the crucial process of photoinduced charge separation. Computational studies can provide insights into this fundamental process and suggest molecular components and interfaces that feature optimal energy-level alignment before time-consuming trial-and-error experimental realization. Here, we use a combination of density functional based tight binding and an extended Huckel approach to perform quantum classical simulations of photoinduced electron injection in a TiO2 dye-sensitized photoanode with explicit solvation at a reasonable computational cost. In particular, we evaluate injection capabilities of core-extended naphthalene diimide (NDI) dyes with three different anchoring groups. Our results stress the importance of nuclear motion as well as conformational and trajectory sampling for a realistic description of the injection process. Furthermore, explicit solvation highly influences the conformational space explored by the dye and anchoring molecules, especially concerning the adsorption mode. Taking these effects into account, the core-extended NDI with a catechol-based anchoring moiety is shown to be the most promising ultrafast electron injector. Our strategy allows for a more systematic computational search for appropriate molecular chromophores in dye-sensitized devices for solar energy conversion.

FABRICATION AND CHARACTERIZATION OF NATURAL DYESENSITIZED SOLAR CELLS BASED ON PbS NANOSTRUCTURES

Natural dye-sensitized solar cells were fabricated based on differently shaped Lead Sulfide nanoparticles in a simple cost-effective way. The grown PbS nanoparticles were characterized by TEM, XRD, Optical Absorption, and Photoluminescence study. The natural dye-sensitized solar cell was fabricated using a kind of dye from Clitoria ternatea as a sensitizer. The current-voltage data of the dye-sensitized solar cell was taken under dark and light illuminated conditions. The dye-sensitized solar cell efficiency was measured and the ideality factor, fill factor were also found out. The open-circuit voltage and short circuit current density of the dye-sensitized solar devices based on three different shaped PbS nanoparticles are also obtained and compared.

Organic dye-sensitized f-MWCNTs-TiO2 composite for optically controlled resistive switching memory applications

Abstract Herein, we have developed organic dye (turmeric) sensitized functionalized multi-walled carbon nanotubes (MWCNTs)-titanium dioxide (TiO2) composite and investigated it's optically controlled resistive switching (RS) and non-volatile memory properties. The composite was synthesized using a single-step hydrothermal method and the dye sensitization period was varied to investigate the effect of the dye loading time (6, 12, 18, and 24 h) on the different properties of the composite. The structural, morphological, and optical properties of the bare and dye-sensitized composites were characterized using X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, and UV–visible spectrometer. The electrical properties of the bare and dye-sensitized composite based devices were tested in the dark, UV, visible, and UV + visible light illumination conditions. Due to the good absorbance properties of the TiO2 in UV region and dye in the visible region, the dye-sensitized composite devices show excellent bipolar RS and non-volatile memory properties in the UV + visible light illumination condition. In this work, the 18 h dye-sensitized device shows superior optical RS properties than other devices. The memristive properties of the optimized devices are reported and demonstrated that the UV + visible light illumination condition provides double valued charge-flux property and best in class charge driving capability. The electrical transport and possible optically controlled RS mechanisms are discussed. The results suggested that the optical stimulus can be an additional parameter in conjunction with the electric stimulus to control the RS properties of the devices.

Power matrix of OPV mini-module under steady conditions of temperature and irradiance at large-area solar simulator

The knowledge of electrical current-voltage (I-V) characteristics of photovoltaic (PV) devices under various irradiance, temperature, and spectral conditions is essential for evaluating the output power and energy production of the devices under various climate conditions. The methods to measure the temperature and irradiance dependences of PV devices power are described in the standards IEC 60891 and IEC 61853-1. Newer PV technologies like organic (OPV) and dye-sensitized (DSSC) devices are rapidly evolving and considerable research effort has addressed alternative approaches to increase efficiency with promising values achieved in the last years. Measurements of the irradiance (G) and temperature (T) dependence of these emerging PV technologies are less established –when available– than those of Si-based devices. In this paper we present a first attempt of power-rating measurement for an OPV mini-module. The measurements were performed with a large-area steady-state solar simulator on a reduced (T,G) range compared to what the standard IEC 61853-1 requires. Nevertheless, they were sufficient to calculate the relative temperature coefficients alpha and beta, which have been satisfactorily compared to previous published values. Also, they provided a first data set for the irradiance dependence of OPV device performance. Finally, the power matrix built from these measurements represents at our knowledge the first data set available for energy rating of OPV technology, as the matrix was done for a single device and for both irradiance and temperature dependencies together.

Chemical potentials of electric double layers at metal-electrolyte interfaces: dependence on electrolyte concentration and electrode materials, and application to field-effect transistors.

When a metal is soaked in an electrolyte solution, the metal and solution affect each other through the formation of electric double layers (EDLs) at their interfaces. The EDLs at metal-electrolyte interfaces can realize high-density charge-carrier injections and accumulations, and thus have recently attracted attention for their potential application to energy storage, and electronic and electrochemical devices. In such EDL-based devices, including field-effect transistors (FETs), the potential energy of surface electrons in the metal electrodes (EM) governs the transistor device performance. This is in clear contrast to redox-driven electrochemical devices such as dye-sensitized solar cells and electrochromic devices, whose performance is primarily governed by the potentials of the redox-active species. However, there has been no systematic research to bridge the distance between metal electrons and electrolyte ions. In the present study, we carefully examined the dependence of EM of ITO, Au and Pt electrodes on the concentration of the PEG solutions of LiCl and MgCl2, because it has been well established that the chemical potential of electrolyte solutions is dependent on the solution concentrations. Our results showed that, at the same electrolyte concentration, the values of EM increased in the order of ITO, Au and Pt; moreover, on the same electrode, EM showed linear decreases as a function of the logarithm of the electrolyte concentrations. To understand these behaviors, we developed a theoretical treatment of the EDLs based on the simple Gouy-Chapman model, and obtained the theoretical expressions of EM in terms of the concentration of electrolyte and the work function of the metal electrode (ΦM), which were found to successfully explain the dependences of EM on the electrolyte concentration and the electrode materials. We also examined the EDL-FETs of platinum phthalocyanine (PtPc), with various LiCl-PEG solutions of different concentrations as gate electrolytes. The threshold voltage eVT and EM exhibited a linear relation, which was well explained by the relation between EM and the valence band energy EVB of PtPc. The transfer characteristics at various gate voltage VG were found to be well normalized by a function of eVG + EM.

New pyran-based molecules as both n- and p-type sensitizers in semi-transparent Dye Sensitized Solar Cells

We report here on the synthesis of four novel pyran-based DSSC photosensitizers. The dyes are constituted of a pyran core functionalized with different electron acceptor groups and with peripheral cyano-acrylic groups. The molecules were carefully characterized for what concerns optical and electrochemical properties and a clear dependence from the strength of the electron-acceptor group functionalizing the pyran core was observed. A detailed DFT analysis on the dyes gave a better insight of the electronic properties and showed a good accord with the experimental properties. The dyes were used as photosensitizers both in n-type and p-type DSSCs. In the first case, the stabilization of the LUMO achieved partially prevented a fast kinetics of the electron injection. To overcome this, we used an I-based electrolyte containing an excess of LiI: the photoconversion efficiency significantly increases for all the dye-sensitized devices, up to a maximum of 2.1%. The dyes were successfully employed the as photosensitizers in p-type DSSC, obtaining PCEs approaching 0.1%, a promising result in the field on NiO-based devices. More remarkably, as far as we are aware, this is the first paper in which a single series of dyes is effectively employed as sensitizers in both n and p-type DSSCs.

Tunable visible-light excitonic absorption and high photoconversion efficiency in two-dimensional group-VI monolayer materials

Recent discovery of tellurene, a two-dimensional (2D) allotrope of tellurium (Te), has effectively extended the realm of 2D materials to group VI. In this paper, we have proceeded to determine the electronic and excitonic optical properties of 2D tellurene and selenene, together with stable monolayer ${\mathrm{TeSe}}_{2}$ in this group, by means of the GW-Bethe-Salpeter equation approach. We find that these materials stabilized in $1\mathrm{T}\text{\ensuremath{-}}{\mathrm{MoS}}_{2}$-like structure appear to be indirect semiconductors and possess ultrahigh isotropic carrier mobilities, which outperform their 2D ${\mathrm{MoS}}_{2}$ counterpart. The exciton is found to be strongly bound and thermally stable at room temperature with a binding energy of 0.37, 0.53, and 0.54 eV, respectively, for the three types of monolayers. Strikingly, we find that the optical gaps of monolayer selenene and ${\mathrm{TeSe}}_{2}$ lie in the ideal energy window of $1.0--1.5\phantom{\rule{0.16em}{0ex}}\mathrm{eV}$ corresponding to the maximum photoconversion efficiency. The number of layers in the stack further provides an effective means to tune the absorption edge across a wide energy range. These characteristics combined with the strong optical absorbance in the whole visible-light region make both 2D materials promising in the applications of efficient, ultrathin, and flexible photovoltaic devices with upper bounds to the conversion efficiency that rivals organic and dye-sensitized devices.

Effects of physical orientation of dye molecules and molecular orbitals on performance of solid-state dye sensitized solar cells.

Performance of Dye-sensitized devices depends on the photon absorption and carrier injection properties of the sensitizer (dye). The orientation of the dye molecule affects the photon absorption cross-section, injection efficiency and carrier transport. These effects are studied, using three variants of cyanine dyes in n-TiO2/Dye/p-CuSCN heterojunction. The results show correlation of dye-molecule's orientation on the short-circuit-photocurrent (Isc). The open-circuit-voltage (Voc) is also subjective. The orientation of the dye molecule influence the photon-harvesting efficiency and obstruct the hole-conductor penetrating onto the working-electrode. Additionally, Cumulative effects of e-e, e-h, spin-coupling and HOMO/LUMO distribution are identified.

Diphenylisobenzofuran Bound to Nanocrystalline Metal Oxides: Excimer Formation, Singlet Fission, Electron Injection, and Low Energy Sensitization

We report the photophysical properties of the dicarboxylated diphenylisobenzofuran dye (1) bound to nanocrystalline metal oxide surfaces. With increased surface loading of 1, emission from the films is significantly quenched but with a small amount of excimer emission at maximum surface loadings. Long-lived triplets were observed by ns TA spectroscopy that are consistent with singlet fission occurring on mesoporous ZrO2. The evolution of these triplets, however, could not be convincingly resolved by our subnanosecond TA spectroscopy. Dye-sensitized devices composed of 1 on a TiO2|Al2O3 core–shell structure exhibited an unusual decrease, increase, and then decrease in Jsc with respect to the thickness of Al2O3. In these films the Al2O3 acts as a tunneling barrier to slow electron injection from the singlet excited state such that singlet fission, and electron injection from the triplet state becomes competitive. Proof-of-principle self-assembled bilayer films that exhibit efficient triplet energy transfer ...

Fundamental Factors Impacting the Stability of Phosphonate-Derivatized Ruthenium Polypyridyl Sensitizers Adsorbed on Metal Oxide Surfaces.

A series of 18 ruthenium(II) polypyridyl complexes were synthesized and evaluated under electrochemically oxidative conditions, which generates the Ru(III) oxidation state and mimics the harsh conditions experienced during the kinetically limited regime that can occur in dye-sensitized solar cells (DSSCs) and dye-sensitized photo-electrosynthesis cells, to further develop fundamental insights into the factors governing molecular sensitizer surface stability in aqueous 0.1 M HClO4. Both desorption and oxidatively induced ligand substitution were observed on planar fluorine-doped tin oxide (FTO) electrodes, with a dependence on the E1/2 Ru(III/II) redox potential dictating the comparative ratios of the processes. Complexes such as RuP4OMe ( E1/2 = 0.91 vs Ag/AgCl) displayed virtually only desorption, while complexes such as RuPbpz ( E1/2 > 1.62 V vs Ag/AgCl) displayed only chemical decomposition. Comparing isomers of 4,4'- and 5,5'-disubstituted-2,2'-bipyridine ancillary ligands, a dramatic increase in the rate of desorption of the Ru(III) complexes was observed for the 5,5'-ligands. Nanoscopic indium-doped tin oxide thin films (nanoITO) were also sensitized and analyzed with cyclic voltammetry, UV-vis absorption spectroscopy, and X-ray photoelectron spectroscopy, allowing for further distinction of desorption versus ligand-substitution processes. Desorption loss to bulk solution associated with the planar surface of FTO is essentially non-existent on nanoITO, where both desorption and ligand substitution are shut down with RuP4OMe. These results revealed that minimizing time spent in the oxidized form, incorporating electron-donating groups, maximizing hydrophobicity, and minimizing molecular bulk near the adsorbed ligand are critical to optimizing the performance of ruthenium(II) polypyridyl complexes in dye-sensitized devices.

Effect of Structural Fluctuations on Elastic Lifetimes of Adsorbate States: Isonicotinic Acid on Rutile(110)

We sample ab initio molecular dynamics trajectories to address the impact of structural fluctuations on elastic lifetimes of adsorbate states at room temperature focusing on heterogeneous charge injection from isonicotinic acid as a key anchoring unit in dye-sensitized energy devices. Complementing related theoretical studies, we employ a Green’s function technique based on density functional theory to account for a fully semi-infinite substrate of rutile TiO2(110). We address the effect of a core-excitation enabling direct comparison with soft X-ray experiments. We find that room temperature fluctuations drastically improve the agreement with experimental lifetime measurements while the core–hole plays an important role shifting the spectra and reducing the electron vibrational coupling of the adsorbate states. Ultimately, the emerging resonance spectra highlight the role of the continuum of acceptor states in temperature broadened Voigt-type profiles.

Design of butterfly type organic dye sensitizers with double electron donors: The first principle study

In this work, we designed a series of butterfly type organic dyes, named ME07-ME13 by introducing such as triphenylamine, phenothiazine, coumarin groups etc. as electron donors and further investigated their absorption spectra using density functional theory (DFT) and time-dependent DFT (TDDFT). All designed dyes cover the entire visible absorption spectrum from 300 to 800nm. It's fascinating that ME13 molecule has two absorption peak and the molar coefficient of two absorption peaks are above 4.645×104M−1·cm−1. The light absorption area of ME13 exhibits an increment of 16.5–19.1% compared to ME07-ME12. Furthermore, we performed a detailed analysis on their geometrical and electronic properties, including molecular structures, energy levels, light harvesting efficiency (LHE), driving force (ΔGinject), regeneration (ΔGregen),electron dipole moments (μnormal), intermolecular electron transfer and dye/(TiO2)38 system electron transitions. The results of calculation reveal that double coumarin donors in ME13 are promising functional groups for butterfly type organic dye sensitizers. It is expected that the design of double donors can provide a new strategy and guidance for the investigation in high efficiency dye-sensitized devices.