Effect of π-Bridge Chain Rearrangement in a Sensitizer on Photovoltaic Performance of Dye-Sensitized Solar Cells

In this paper, novel triphenylamine (TPA)-based photosensitizers (YY-ThP, YY-PTh, YY-TTP, and YY-PTT) with a donor-π-acceptor (D-π-A) structure are developed for dye-sensitized solar cells by rearrangement of planar thiophene and thienothiophene with a benzene ring as a π-bridging chain. Density functional theory calculations are performed to obtain the HOMO-LUMO electron cloud density distribution, dipole moment (μ), intermolecular torsion angle (θ), three-dimensional (3D) molecular structure, and electrostatic potential surface (ESP) maps of the dyes. The effects of π-bridge chain rearrangement and dye cosensitization on the photophysical, electrochemical, and photovoltaic properties of the devices are investigated through experiment analysis. The results showed that the dye YY-ThP with the thiophene group in the π-bridged chain linked to the TPA donor has the largest μ (14.74 D) and the smallest θ (17.48°), and the electron-withdrawing thiophene group enabled this π-bridged chain with a faster intramolecular charge transfer, which made it exhibit the best energy conversion efficiency (PCE = 4.78%). Furthermore, cosensitization of the YY-ThP+YY-PTh device in an equimolar ratio minimizes lateral electron migration and dark current generation, achieving the highest PCE (5.28%).

Photoexcited Intramolecular Charge Transfer in Dye Sensitizers: Predictive In Silico Screening for Dye-Sensitized Solar Cell Devices

Efficient photoinduced intramolecular charge transfer (ICT) from donor to acceptor in dye molecules is the functional basis and key property in the working of a dye-sensitized solar cell (DSSC). To understand the ICT process in photoexcited dye molecules, we analyze the electronic properties and structural parameters of a chosen set of experimentally synthesized donor-acceptor (D-A) and donor-π-spacer-acceptor (D-π-A) type dye molecules in their ground, excited, and cationic states. The correlation between structural modification and charge redistribution in different parts of the molecule helps to identify the extent of π-conjugation and spatial rearrangement of electron density localization along the molecular skeleton. We find that prominent twisting of several groups and the resulting molecular bond rearrangements in larger parts of the molecule promote efficient donor to acceptor ICT, such as in D-A type ADEKA1 and C275 dyes. Thus, based on the modest computation of structural and electronic properties of dye molecules in their respective ground, excited, and cationic states, we identify the desired structural changes that facilitate tunable intramolecular charge transfer to highlight a simple and direct prescription to screen out probable efficient dye molecules among many samples. Our approach complements recent experimental evidence of capturing the structural view of the excited-state charge transfer in molecules.

Assessment of time-dependent density functionals for the electronic excitation energies of organic dyes used in DSSCs

The absorption spectra modeled as the vertical excitation energies of 13 dye sensitizers used in dye-sensitized solar cells (DSSCs) are benchmarked by means of time-dependent (TD)-DFT, using 36 functionals from different DFT rungs.

Effect of Extending the Conjugation of Dye Molecules on the Efficiency and Stability of Dye-Sensitized Solar Cells

We designed and synthesized two organic dyes (A6 and A10) for dye-sensitized solar cells (DSSCs) by extending the molecular conjugation strategy. The sensitizer A10 was constructed by inserting ethene into our previously reported sensitizer AZ6. The sensitizer A6 was obtained by further substituting the hydrogen of ethene with another donor (D) and π-bridge-acceptor (π-A) segment. The UV-vis spectra and J-V curves showed that the dyes A10 and A6 could effectively facilitate the light-harvesting and photocurrent densities with respect to AZ6. Consequently, the A10-based DSSC achieved an enhanced efficiency (8.54%) with a high photocurrent (18.81 mA cm^-2). Desorption experiments of dyes adsorbed on TiO₂ showed that compared with the monoanchoring dyes AZ6 and A10, the dianchoring configuration effectively strengthened the affinity of dye A6 with the photoanode, making it more difficult to leach from the photoanode. The A6-based DSSC shows outstanding stability, and its overall efficiency could remain 98.0% of its initial value after 3000 h of aging time, exceeding that of its monoanalogue AZ6 (remained 78.3% after 3000 h).

Charge transfer and opto-electronic properties of some newly designed polycatenar discotic liquid crystal derivatives: a DFT study

Herein, we demonstrate effect of substituents on optoelectronic properties of discotic liquid crystals (DLCs) by using density functional theory (DFT) calculations at B3LYP/Lanl2Z level of theory. Three parent DLCs, namely, (1) benzene-1,3,5-triyl tris(3,5-dialkoxybenzoate), (2) N¹, N³, N⁵-tris(3-alkoxyphenyl)benzene-1,3,5-tricarboxamide, and (3) trialkyl 4, 4', 4″-(benzenetricarbonyltris (azanediyl)) tribenzoate benzoate and their -N and -S group derivatives of 1, 2, and 3, were investigated to observe the change in optoelectronic response of these systems. The frontier molecular orbital studies and electron affinity values indicate that the studied compounds are stable against the oxygen and moisture present in air. The calculated charge transfer integrals, electron, and hole mobility values revealed that parent DLCs and their derivatives can be employed as an effective n-type material for OLEDs; however, derivatives have enhanced charge transfer values compared with their parents. For better understanding of the thermochemistry and effect of substituents, frequency calculations were carried out. P₁-D₄ derivative having R = -NH-CO-CH₃ terminal group came out to be theoretically the most favored having the lowest ΔG value. Computed UV/visible spectroscopic analysis showed minimum absorbance and maximum transmittance for derivative P₂-D₁ having -S-NH₂ substituent. Molecular electrostatic potential surfaces mapped at potential range, i.e., - 8.531e-3esu to + 8.531e-3esu, describe electrophilic and nucleophilic characteristics. Introduction of electron donor groups enhanced electrical conductivity, excitation energy, and charge transfer integral, thus increasing optoelectronic properties of DLCs. However, these claims require further experimental verification.

Highly fluorescent triazolopyridine-thiophene D-A-D oligomers for efficient pH sensing both in solution and in the solid state

Conjugated fluorophores have been extensively used for fluorescence sensing of various substances in the field of life processes and environmental science, due to their noninvasiveness, sensitivity, simplicity and rapidity. Most existing conjugated fluorophores exhibit excellent light-emitting performance in dilute solutions, but their properties substantially decrease or even completely vanish due to severe aggregation quenching in the solid state. Herein, we synthesize a series of triazolopyridine-thiophene donor-acceptor-donor (D-A-D) type conjugated molecules with high absolute fluorescence quantum yields (ΦF) ranging from 80% to 89% in solution. These molecules also show unusual light-emitting properties in the solid state with ΦF of up to 26%. We find that owing to the protonation-deprotonation process of the pyridine ring, these compounds display obvious changes in both fluorescence wavelength and intensity upon addition of acids, and these changes can be readily recovered by the successive introduction of bases. By harnessing this phenomenon, we further show that these fluorophores can be employed for efficient and reversible fluorescence sensing of hydrogen ions in a broad pH range (0.0-7.0). With the fabrication of pH testing papers and ink-printed complex patterns including butterflies and letters on substrates, we demonstrate the application of such sensors to fluorescence indication or solid state pH detection for real samples such as volatile acidic/basic gas and water-quality analysis.

Synthesis of dipyrrolopyrazine-based sensitizers with a new π-bridge end-capped donor–acceptor framework for DSSCs: a combined experimental and theoretical investigation

Organic dyes with dipyrrolopyrazine as the central π-linker have been synthesized. Photovoltaic properties were investigated and supported by DFT. Thermal analysis shows good thermal stability.

Dual-purpose zinc and silicon complexes of 1,2,3-triazole group substituted phthalocyanine photosensitizers: synthesis and evaluation of photophysical, singlet oxygen generation, electrochemical and photovoltaic properties

The synthesis, photophysical, singlet oxygen generation, electrochemical and photovoltaic properties of peripheral and axial 1,2,3-triazole group substituted zinc and silicon phthalocyanine complexes with strong absorption in the visible region were described. All novel complexes have been characterized by spectroscopic and electrochemical techniques. All the new compounds are highly soluble in most common organic solvents. The electronic absorption and fluorescence spectral properties of complexes 4 and 5 are investigated. The effects of the triazole group, different metal centers and position of the substituent on the photophysical, electrochemical and photovoltaic properties of the new phthalocyanines were also investigated for the first time in this work. According to the fluorescence measurements, the axially substituted silicon complex (5) showed higher fluorescence quantum yield (Φ_F = 0.28) than the peripherally substituted zinc complex (4). In addition, quantum yields for singlet oxygen generation (Φ_Δ = 0.32 for silicon complex (4) and Φ_Δ = 0.76 for zinc complex (5) in DMSO) were obtained. Electrochemical studies show that complex 5 is present in non-aggregated form as a result of steric hindrance of the axial groups; the LUMO level of this complex is slightly more negative than the conduction band of TiO₂ and electron injection might be less effective. Therefore, the power conversion efficiency of 1.30% for a complex 4 based dye-sensitized solar cell (DSSC) is higher than complex 5 (0.90%). Consequently, these zinc and silicon complexes are promising candidates not only for photodynamic therapy but also solar power conversion.

Evaluation of dual-purpose zinc and silicon phthalocyanine complexes on photophysical, singlet oxygen generation, electrochemical and photovoltaic properties.

Effects of Pyrazine Derivatives and Substituted Positions on the Photoelectric Properties and Electromemory Performance of D⁻A⁻D Series Compounds

Pyrazine derivatives quinoxaline and pyridopyrazine were selected as the acceptors, and benzocarbazole was used as the donor to synthesize four different D⁻A⁻D compounds. The results showed that 2,3-bis(decyloxy)pyridine[3,4-b]pyrazine (DPP) exhibited stronger electron-withdrawing ability than that of 2,3-bis(decyloxy)quinoxaline (DPx), because DPP possesses one more nitrogen (N) atom, resulting in a red-shift of the intramolecular charge transfer (ICT) absorption bands and fluorescent emission spectra for compounds with DPP as the acceptor compared with those that use DPx as the acceptor. The band-gap energy (Eg) of the four D⁻A⁻D compounds were 2.82 eV, 2.70 eV, 2.48 eV, and 2.62 eV, respectively, for BPC-2DPx, BPC-3DPx, BPC-2DPP, and BPC-3DPP. The solvatochromic effect was insignificant when the four compounds were in the ground state, which became significant in an excited state. With increasing solvent polarity, a 30⁻43 nm red shift was observed in the emissive spectra of the compounds. The thermal decomposition temperatures of the four compounds between 436 and 453 °C had very high thermal stability. Resistor-type memory devices based on BPC-2DPx and BPC-2DPP were fabricated in a simple sandwich configuration, Al/BPC-2DPx/ITO or Al/BPC-2DPP/ITO. The two devices showed a binary non-volatile flash memory, with lower threshold voltages and better repeatability.

Movement of new direction from conjugated polymer to semiconductor composite polymer nanofiber

In the past few years, there was a tremendous growth in conjugated polymer nanofibers via design of novel conjugated polymers with inorganic materials. Synthetic routes to these conjugated polymers involve new, mild polymerization techniques, which enable the formation of well-defined polymer architectures. This review provides interest in the development of novel (semi) conducting polymers, which combine both organic and inorganic blocks in one framework. Due to their ability to act as chemosensors or to detect various chemical species in environmental and biological systems, fluorescent conjugated polymers have gained great interest. Nanofibers of metal oxides and sulfides are particularly interesting in both their way of applications and fundamental research. These conjugated nanofibers operated for many applications in organic electronics, optoelectronics, and sensors. Synthesis of electrospun fibers by electrospinning technique discussed in this review is a simple method that forms conjugated polymer nanofibers. This review provides the basics of the technique and its recent advances in the formation of highly conducting and high-mobility polymer fibers towards their adoption in electronic application.

Effects of Internal Electron-Withdrawing Moieties in D-A-π-A Organic Sensitizers on Photophysical Properties for DSSCs: A Computational Study

D-A-π-A dyes differ from the traditional D-π-A framework having several merits in dye-sensitized solar cell (DSSC) applications. With regard to D-π-A dyes, D-A-π-A dyes red-shift absorption spectra and show particular photostability. Nevertheless, the effects of internal acceptor on the charge transfer (CT) probability are unclear. We employed density functional theory (DFT), time-dependent DFT (TD-DFT), and TD-DFT molecular dynamics (MD) simulations to investigate the effects of internal acceptor on the photophysical properties of D-A-π-A dyes on DSSCs. Our calculations show the absorption bands of D-A-π-A dyes with strong electron-withdrawing internal acceptors exhibiting significant characteristics of dual CT; the excited electron density is transferred to the internal and terminal acceptors simultaneously. Particularly, the internal acceptor traps a significant amount of electron density upon photoexcitation. The TD-DFT MD simulations at 300 K show that only a small amount of excited electron density is pushing and pulling between the internal acceptor and terminal acceptor moieties; the thermal energy is not high enough to drive the electron density from the internal acceptor to the terminal acceptor. Our study reveals the nature of CT bands of D-A-π-A dyes providing a theoretical basis for further rational engineering.

Propping the optical and electronic properties of potential photo-sensitizers with different π-spacers: TD-DFT insights

We report density functional theory (DFT) and time-dependent density functional theory (TD-DFT) calculations on the widely used N3 dye (cis-[Ru(2,2'-bipyridine-4,4'-dicarboxylic acid)₂(NCS)₂] and its trans isomer with different π-spacers. The study compared the sensitization properties of the two isomers in terms of their electronic properties such as light harvesting efficiency (LHE), absorbed wavelength (λ_Max) and molecular orbital distribution. Also, charge transfer descriptors, such as the charge transfer distance (D^CT), dipole moment (μ^CT), and the amount of charge transferred (q^CT) were investigated. Upon replacing the two "2,2'-bipyridine-4,4'-dicarboxylic acid" ligands of the N3 dye with extended π-spacers of "1,4-benzene and 2,5-thiophene" for both the cis and trans isomers, the LHE of the trans isomer was increased by 70% compared to the cis counterpart. The complexes with thiophene spacers showed the highest LHE. The trans isomers showed wider absorbance range of wavelengths and equal wide distribution of charge density in the excited state along the organic ligands. These findings highlight the importance of using π-spacers between the organic ligands and the carboxylate groups to boost the LHE of DSSCs. Also, our study showed that the trans isomer is superior in its optical and electronic properties than the cis counterpart. However, the trans isomer is yet to be tested experimentally in DSSCs.

Organic Photosensitizers Incorporating Rigid Benzo[1,2-b:6,5-b']dithiophene Segment for High-Performance Dye-Sensitized Solar Cells

Benzo[1,2-b:6,5-b']dithiophene (BDT) entity with rigid skeleton is introduced into the conjugated spacer of organic dyes, with triphenylamine as the electron donor and 2-cyanoacrylic acid as the acceptor, have been prepared for dye-sensitized solar cells. Inserting an aromatic entity between BDT and the anchor extends the absorption wavelength of the dyes and improves the dark current suppression efficiency, and consequently leads to better cell performance. Addition of chenodeoxycholic acid coadsorbent alleviates dye aggregation and results in better cell efficiency. The dye inserted with 4H-cyclopenta[2,1-b:3,4-b']dithiophene entity achieves the best efficiency (9.11%) when I^-/I₃^- was used as the electrolyte. When Co(phen)₃^2+/3+ was used as the electrolyte, the efficiency further boosts to 9.88%.

High-Performance Porphyrin-Based Dye-Sensitized Solar Cells with Iodine and Cobalt Redox Shuttles

Recently, enormous research passion has been devoted to enhance the power conversion efficiency (PCE) of porphyrin sensitizers for dye-sensitized solar cells (DSSCs), but the major stumbling block is the absorption defect in the visible-light region. To address this challenge, high-performance DSSCs are reported based on a new donor-π-acceptor sensitizer FW-1, 7H-dibenzo[c,g]carbazole-substituted and fused zinc porphyrin, co-sensitized with a benzotriazole-containing dye (WS-5) in iodine and cobalt redox systems, and high PCEs of 10.21 and 10.42 %, respectively, were obtained. An unprecedented breakthrough was obtained by making one sensitizer suitable for several electrolyte systems because of its appropriate molecular orbitals and co-sensitizer.

Molecular engineering and sequential cosensitization for preventing the "trade-off" effect with photovoltaic enhancement

In dye-sensitized solar cells (DSSCs), it is essential to use rational molecular design to obtain promising photosensitizers with well-matched energy levels and narrow optical band gaps. However, the "trade-off" effect between the photocurrent and photovoltage is still a challenge. Here we report four benzoxidazole based D-A-π-A metal-free organic dyes (WS-66, WS-67, WS-68 and WS-69) with different combinations of π-spacer units and anchoring-acceptor groups. Either extending the π-spacer or enhancing the electron acceptor can efficiently modulate the molecular energy levels, leading to a red-shift in the absorption spectra. The optimal dye, WS-69, containing a cyclopentadithiophene (CPDT) spacer and cyanoacetic acid acceptor, shows the narrowest energy band gap, which displays a very high photocurrent density of 19.39 mA cm-2, but suffers from a relatively low photovoltage of 696 mV, along with the so-called deleterious "trade-off" effect. A cosensitization strategy is further adopted for enhancing the device performance. Optimization of the dye loading sequence is found to be capable of simultaneously improving the photocurrent and photovoltage, and distinctly preventing the "trade-off" effect. The superior cosensitized cell exhibits an excellent power-conversion efficiency (PCE) of 10.09% under one-sun irradiation, and 11.12% under 0.3 sun irradiation, which constitutes a great achievement in that the efficiency of a pure metal-free organic dye with iodine electrolyte can exceed 11% even under relatively weak light irradiation. In contrast with the previous cosensitization strategy which mostly focused on compensation of light-harvesting, we propose a novel cosensitization architecture, in which the large molecular-sized, high photocurrent dye WS-69 takes charge of broadening the light-harvesting region to generate a high short-circuit current (JSC) while the small molecular-sized, high photovoltage dye WS-5 is responsible for retarding charge recombination to generate a high open-circuit voltage (VOC). In addition, adsorption amount and photo-stability studies suggest that the cyano group in the anchoring acceptor is important for the stability since it is beneficial towards decreasing the LUMO levels and enhancing the binding of dyes onto TiO2 nanocrystals.

A new fluoropyrido[3,4-b]pyrazine based polymer for efficient photovoltaics

Using a fluoropyrido[3,4-b]pyrazine based 2D-conjugated polymer as an electron donor in polymer solar cells, a power conversion efficiency of 6.2% is obtained, which is the highest PCE among the PP-based polymers reported to date.

Controlling light absorption and photoelectric properties of coumarin-triphenylaminedye by different acceptor functional groups

The ground state and excited state properties of three coumarin dyes, ZCJ1, ZCJ2 and ZCJ3, including ground state structures, energy levels, absorption spectra and driving forces of electron injection, were investigated via density functional theory (DFT) and time-dependent density functional theory (TD-DFT). In addition, five new molecules ZCJ3-1, ZCJ3-2, ZCJ3-3, ZCJ3-4 and ZCJ3-5 were designed through the introduction of a -CN group into molecule ZCJ3. The ground state and excited state properties of the five designed molecules were also calculated and compared with that of the original molecule, aiming to investigate the effect of different position of -CN groups on the optical and electrical properties of dye molecules. Moreover, the external electric field was taken into account. The results indicated that all three original molecules have better absorption within the visible-light range, and the molecule with a thiophene-thiophene conjugated bridge enables a red shift of the absorption spectrum. The molecule with a thiophene-benzene ring conjugated bridge enables the increase of driving force of electron injection. The energy levels, spectra and driving force of electron injection for the designed molecules are discussed in terms of studying their potential utility in dye-sensitized solar cells.

Bi-anchoring Organic Dyes that Contain Benzimidazole Branches for Dye-Sensitized Solar Cells: Effects of π Spacer and Peripheral Donor Groups

Benzimidazole-branched bi-anchoring organic dyes that contained triphenylamine/phenothiazine donors, 2-cyanoacrylic acid acceptors, and various π linkers were synthesized and examined as sensitizers for dye-sensitized solar cells. The structure-activity relationships in these dyes were systematically investigated by using absorption spectroscopy, cyclic voltammetry, and density functional theory calculations. The wavelength of the absorption peak was more-heavily influenced by the nature of the π linker than by the nature of the donor. For a given donor, the absorption maximum (λmax ) was red-shifted on changing the π linker from phenyl to 2,2'-bithiophene, whilst the dyes that contained triphenylamine units displayed higher molar extinction coefficients (ϵ) than their analogous phenothiazine-based triphenylamine dyes, which led to good light-harvesting properties in the triphenylamine-based dyes. Electrochemical data for the dyes indicated that the triphenylamine-based dyes possessed relatively low-lying HOMOs, which could be beneficial for suppressing back electron transfer from the conduction band of TiO2 to the oxidized dyes, owing to facile regeneration of the oxidized dye by the electrolyte. The best performance in the DSSCs was observed for a dye that possessed a triphenylamine donor and 2,2'-bithiophene π linkers. Electron impedance spectroscopy (EIS) studies revealed that the use of triphenylamine as the donor and phenyl or 2,2'-bithiophene as the π linkers was beneficial for disrupting the dark current and charge-recombination kinetics, which led to a long electron lifetime of the injected electrons in the conduction band of TiO2 .

Unveiling iodine-based electrolytes chemistry in aqueous dye-sensitized solar cells

Aqueous dye-sensitized solar cells (DSSCs) have recently emerged as promising systems, which can combine low cost and environmental compatibility with appreciable efficiency, long-term durability and enhanced safety. In the present study, we thoroughly investigate the chemistry behind the iodide/triiodide-based redox mediator, which presents - in a completely aqueous environment - several differences when compared to the behavior observed in the conventionally used organic solvents. The speciation of ions, the effect of the concentration of the redox mediator and the type of counter-ion are characterized from the electrochemical, spectroscopic, photovoltaic and analytical viewpoints. Furthermore, we demonstrate that aqueous DSSCs, often assumed as unstable, hold the potential to assure unparalleled stability after five months of aging without any addition of stabilizers or gelling agents, thus envisaging the construction of eco-friendly photovoltaic devices free of expensive, flammable and toxic solvents.

Broad spectral-response organic D–A–π–A sensitizer with pyridine-diketopyrrolopyrrole unit for dye-sensitized solar cells

In this work, four D–A–π–A sensitizers PDPP-I–IV based on pyridine-flanked DPP moieties (PDPP) were designed and synthesized for broadly spectral-response in dye-sensitized solar cells.

Push–pull type alkoxy-wrapped N-annulated perylenes for dye-sensitized solar cells

Three push–pull type, alkoxy-wrapped N-annulated perylene based sensitizers were synthesized and power conversion efficiency up to 8.38% was achieved.

Unprecedentedly targeted customization of molecular energy levels with auxiliary-groups in organic solar cell sensitizers

Lowering the LUMOs and decreasing energy “waste” is targeted through inserting an auxiliary group from an electron donor or acceptor into D–π–A organic sensitizers, and the photovoltaic efficiency increases 38 fold from 0.24 to 9.46%.

In dye-sensitized solar cells (DSSCs), the HOMO–LUMO energy gap of organic sensitizers should be large enough to enable efficient electron injection and dye regeneration. However, the LUMOs of most practical organic dyes are always too high, making energy “waste”. In order to deepen the LUMOs, we focus on the targeted modulation of the molecular energy levels by embedding an electron donor or acceptor into the skeleton of a typical D–π–A model. The electron-rich group of 3,4-ethylenedioxythiophene (EDOT) lifts up the HOMO level with little influence on the LUMO, while the electron-deficient group of benzothiadiazole (BTD) or benzooxadiazole (BOD) mainly lowers the customized LUMO level. As a consequence, the auxiliary group change from EDOT (dye WS-53) to BOD (dye WS-55) brings forth a huge photoelectric conversion efficiency (PCE) increase by 38 fold from 0.24 to 9.46% based on an I^–/I₃^– redox couple, and even reaching a high PCE of 10.14% with WS-55 under 0.3 sunlight irradiation.

Organic Dyes Incorporating the Dithieno[3,2-f:2',3'-h]quinoxaline Moiety for Dye-Sensitized Solar Cells

New donor-acceptor'-acceptor-type sensitizers (QBT dyes), comprising arylamine as the electron donor, dithieno[3,2-f:2',3'-h]quinoxaline as the internal acceptor, and 2-cyanoacrylic acid as both the acceptor and anchor, have been synthesized. The QBT dyes have broad absorption spectra covering the range of λ=368-487 nm with a highest molar extinction coefficient of up to approximately 40 000 M(-1)  cm(-1) . The light-to-electricity conversion efficiencies of the dye-sensitized solar cells (DSSCs) fabricated from the dyes range from 6.11 to 7.59 % under simulated AM 1.5 G illumination. Upon addition of a threefold concentration of chenodeoxycholic acid as the co-adsorbent, the best performance cell has a power-conversion efficiency of 8.41 %, which is higher than that of the N719-based standard DSSC (8.27 %).

A strategy to design novel structure photochromic sensitizers for dye-sensitized solar cells

Two sensitizers with novel structure were designed and synthetized by introducing photochromic bisthienylethene (BTE) group into the conjugated system. Thanks to the photochromic effect the sensitizers have under ultraviolet and visible light, the conjugated bridge can be restructured and the resulting two photoisomers showed different behaviors in photovoltaic devices. This opens up a new research way for the dye-sensitized solar cells (DSSCs).

Comparative study on pyrido[3,4-b]pyrazine-based sensitizers by tuning bulky donors for dye-sensitized solar cells

Dye-sensitized solar cells (DSSCs) with cobalt electrolytes have gained increasing attention. In this Research Article, two new pyrido[3,4-b]pyrazine-based sensitizers with different cores of bulky donors (indoline for DT-1 and triphenylamine for DT-2) were designed and synthesized for a comparative study of their photophysical and electrochemical properties and device performance and were also analyzed through density functional theory calculations. The results of density function theory calculations reveal the limited electronic communication between the biphenyl branch at the cis-position of N-phenylindoline and the indoline core, which could act as an insulating blocking group and inhibit the dye aggregation and charge recombination at the interface of TiO2/dye/electrolyte. As expected, DSSCs based on DT-1 with cobalt redox electrolyte gained a higher photoelectric conversion efficiency of 8.57% under standard AM 1.5 G simulated sunlight, with Jsc = 16.08 mA cm(-2), Voc = 802 mV, and FF = 0.66. Both electrochemical impedance spectroscopy (EIS) and intensity-modulated photovoltage spectroscopy (IMVS) suggest that charge recombination in DSSCs based on DT-1 is much less than that in their counterparts of DT-2, owing to the bigger donor size and the insulating blocking branch in the donor of DT-1.

New D–A–π–A organic sensitizers for efficient dye-sensitized solar cells

New metal-free D–A–π–A organic sensitizers based on N-annulated perylene derivatives are promising for efficient dye-sensitized solar cells.

Dye-sensitized solar cells with improved performance using cone-calix[4]arene based dyes

Three cone-calix[4]arene-based sensitizers (Calix-1-Calix-3) with multiple donor-π-acceptor (D-π-A) moieties are designed, synthesized, and applied in dye-sensitized solar cells (DSSCs). Their photophysical and electrochemical properties are characterized by measuring UV/Vis absorption and emission spectra, cyclic voltammetry, and density functional theory (DFT) calculations. Calix-3 has excellent thermo- and photostability, as illustrated by thermogravimetric analysis (TGA) and dye-aging tests, respectively. Importantly, a DSSC using the Calix-3 dye displays a conversion efficiency of 5.48 % in under standard AM 1.5 Global solar illumination conditions, much better than corresponding DSSCs that use the rod-shaped dye M-3 with a single D-π-A chain (3.56 %). The dyes offer advantages in terms of higher molar extinction coefficients, longer electron lifetimes, better stability, and stronger binding ability to TiO2 film. This is the first example of calixarene-based sensitizers for efficient dye-sensitized solar cells.

Effects of heterocycles containing different atoms as π-bridges on the performance of dye-sensitized solar cells

The thiophene π-bridge shows a better performance compared with the furan π-bridge in DSSCs.

Organic dyes incorporating the dithieno[3',2':3,4;2″,3″:5,6]benzo[1,2-c]furazan moiety for dye-sensitized solar cells

New D-π-A'-π-A type sensitizers (JH dyes), comprised arylamine as the electron donor, dithieno[3',2':3,4;2″,3″:5,6]benzo[1,2-c]furazan (DTBF) in the conjugated spacer, and 2-cyanoacrylic acid as both the acceptor and anchor, have been synthesized. The JH dyes have broad absorption spectra covering the range of 350 to 600 nm with the highest molar extinction coefficient up to >40 000 M(-1) cm(-1). The dye-sensitized solar cells (DSSCs) fabricated from the dyes exhibited light-to-electricity conversions ranging from 1.42 to 6.18% under simulated AM 1.5 G illumination. Upon adding 10 mM CDCA as the coadsorbent, the best performance cell has the power conversion efficiency of 7.33%, which is close to that of N719-based standard DSSC (7.56%).