New D-π-A-conjugated organic sensitizers based on α-pyranylidene donors for dye-sensitized solar cells

A series of new push-pull organic dyes incorporating a cyanoacrylic acid group as electron acceptor unit and α-chalcogenopyranylidene group (X = S; O) as electron donor unit has been synthesized, characterized and used as sensitizer for dye-sensitized solar cells (DSSCs). For the first time, α-pyranylidene and thiopyranylidene groups, have been evaluated in DSSC. To obtain the thermodynamic values of the solar cell, an investigation of their electrochemical (CV) and optical properties (UV–vis absorption spectroscopy) is also reported.     

Hyperbranched conjugated polymers with donor-π-acceptor architecture as organic sensitizers for dye-sensitized solar cells

Three novel hyperbranched conjugated polymers (H-tpa, H-cya, and H-pca) with the same conjugated core structure and different functional terminal units were synthesized and applied in dye-sensitized solar cells (DSSCs) as photosensitizers. The photophysical, electrochemical and photovoltaic properties of the three hyperbranched conjugated polymers (HBPs) were investigated in detail. The results showed that donor-π-acceptor architecture in hyperbranched molecule benefited intramolecular charge transfer and consequently increased the generation of photocurrent. The three-dimensional (3D) steric configuration of HBPs could effectively suppress the aggregation of dyes on TiO₂ film, which is beneficial for achieving good photovoltaic performances. Among the three hyperbranched dyes, the highest power conversion efficiency (η) of 3.93% (J_sc = 8.78 mA/cm², V_oc = 0.65 V, FF = 0.688) was obtained with a DSSC based on H-pca dye upon the addition of the same mass ratio chenodeoxycholic acid (CDCA) as coadsorbent under AM 1.5 irradiation with 100 mW/cm² simulated sunlight.     

New organic materials based on D–π–A structure for application in dye-sensitized solar cells

Research on Chemical Intermediates - We used density functional theory at B3LYP level with 6-31G(d,p) basis set for all atoms to study the electrochemical, photovoltaic, and absorption properties...     

A new class of cyclometalated ruthenium sensitizers of the type ĈNN for efficient dye-sensitized solar cells

A new class of cyclometalated ruthenium sensitizers incorporating a ?NN ligand and conjugated 2,2'-bipyridine in the ancillary ligand have been designed and synthesized. The photovoltaic performance of JK-206 using an electrolyte containing 0.6 M 1,2-dimethyl-3-propylimidazolium iodide, 0.05 M I(2), 0.1 M LiI, and 0.5 M tert-butylpyridine in CH(3)CN gave a short-circuit photocurrent density of 19.63 mA cm(-2), an open-circuit voltage of 0.74 V, and a fill factor of 0.72, affording an overall conversion efficiency of 10.39%. The efficiency is the highest one reported for dye-sensitized solar cells based on the cyclometalated ruthenium sensitizer of the type ?NN. Moreover, the same device using a polymer gel electrolyte exhibited a remarkable stability under 1000 h of light soaking at 60 °C, retaining 91% of the initial efficiency of 7.14%.     

New D-π-A-conjugated organic sensitizers based on 4H-pyran-4-ylidene donors for highly efficient dye-sensitized solar cells

We have synthesized a series of four new promising D-π-A conjugated organic sensitizers with a proaromatic 4H-pyran-4-ylidene as a donor, a thiophene ring in the bridge, and 2-cyanoacrilic acid as acceptor. Comparison between different donor substituents and the modification of the thiophene ring resulted in molar extinction coefficients as high as 36399 M(-1) cm(-1) at 551 nm. The photovoltaic properties of the DSSCs demonstrate power conversion efficiencies as high as 5.4%.     

A new D–D–π–A dye for efficient dye-sensitized solar cells

New metal-free organic dye sensitizers containing mono-triphenylamine or bis-triphenylamine as the electron donor, a thiophene as the π-conjugated system, and a cyanoacrylic acid moiety as the electron acceptor were synthesized. The optical and electrochemical properties of the dyes were investigated,and their performance as sensitizers in solar cells was evaluated. Dye-sensitized solar cells based on dye containing bis-triphenylamine as the electron donor produced a photon-to-current conversion efficiency of 6.06%(Jsc = 14.21 m A/cm~2, Voc = 0.62 V, ff = 0.69) under 100 m W/cm~2 simulated AM 1.5 G solar irradiation(100 m W/cm~2).     

Reasons for the effect of the amount of electrolyte on the performance of lithium–sulfur cells

As is known, the depth of the electrochemical reduction of sulfur and lithium polysulfides, the reduction rate, and the cycle life of lithium–sulfur cells decrease with the electrolyte content. The present paper studies the reasons for the effect of the amount of electrolyte on the depth of sulfur reduction and the cycle life of lithium–sulfur cells. The main reason for the effect of the amount of electrolyte on the depth of the electrochemical reduction of sulfur was shown to be the generation of solvate complexes of lithium polysulfides. The minimum amount of electrolyte required for complete reduction of sulfur during the discharge of lithium–sulfur cells is determined by the composition of the generated solvate complexes of lithium polysulfides. The solvate numbers of the lithium ion in the solvate complexes of lithium polysulfides generted in sulfolane electrolyte systems were evaluated from the experimental data. An analysis of the results shows that the minimum solvate number of lithium ions in the solvate complexes of lithium polysulfides with sulfolane is 1.     

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

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-4 H-cyclopenta 1,2-b:5,4-b’]dithiophene(M11),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophenethiophene(M12),thiophene-4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M13),4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene-benzene(M14),and 4,4-dimethyl-4 H-cyclopenta[1,2-b:5,4-b’]dithiophene(M15)units asπ-bridges,and cyanoacrylic acid as an electron acceptor/anchor.The extension of theπ-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.     

Organic dyes based on triphenylamine for dye-sensitized solar cells:Structure–property relationships

Three new organic dyes based on triphenylamine with a structure of A-D-A-D-A(D1),A-D-A(D2) and D-A(D3) were designed,theoretically calculated and synthesized for dye-sensitized solar cells.Dye D1 exhibits a broader absorption than D2 and D3,due to the intramolecular charge transfer between the donor triphenylamine and the acceptor benzothiadiazole.Dye D1 exhibits a lower HOMO and a lower LUMO than D2 and D3 due to the electron-withdrawing benzothiadiazole.The number of anchoring group cyanoacrylic acid has no obvious influence on absorption and energy levels of D2 and D3.The LUMO of D1 locates on benzothiadiazole rather than cyanoacrylic acid anchoring groups,while the LUMOs of D2 and D3 are localized on cyanoacrylic acid.D2 and D3 give higher short-circuit current density than D1.D3 with one anchoring group gives the highest open-circuit voltage.Consequently,the D3-based device gives the highest efficiency.     

Constructing organic D-A-π-A-featured sensitizers with a quinoxaline unit for high-efficiency solar cells: the effect of an auxiliary acceptor on the absorption and the energy level alignment

Four organic D-A-π-A-featured sensitizers (TQ1, TQ2, IQ1, and IQ2) have been studied for high-efficiency dye-sensitized solar cells (DSSCs). We employed an indoline or a triphenylamine unit as the donor, cyanoacetic acid as the acceptor/anchor, and a thiophene moiety as the conjugation bridge. Additionally, an electron-withdrawing quinoxaline unit was incorporated between the donor and the π-conjugation unit. These sensitizers show an additional absorption band covering the broad visible range in solution. The contribution from the incorporated quinoxaline was investigated theoretically by using DFT and time-dependent DFT. The incorporated low-band-gap quinoxaline unit as an auxiliary acceptor has several merits, such as decreasing the band gap, optimizing the energy levels, and realizing a facile structural modification on several positions in the quinoxaline unit. As demonstrated, the observed additional absorption band is favorable to the photon-to-electron conversion because it corresponds to the efficient electron transitions to the LUMO orbital. Electrochemical impedance spectroscopy (EIS) Bode plots reveal that the replacement of a methoxy group with an octyloxy group can increase the injection electron lifetime by a factor of 2.4. IQ2 and TQ2 can perform well without any co-adsorbent, successfully suppress the charge recombination from TiO(2) conduction band to I(3)(-) in the electrolyte, and enhance the electron lifetime, resulting in a decreased dark current and enhanced open circuit voltage (V(oc)) values. By using a liquid electrolyte, DSSCs based on dye IQ2 exhibited a broad incident photon-to-current conversion efficiency (IPCE) action spectrum and high efficiency (η=8.50?%) with a short circuit current density (J(sc)) of 15.65?mA?cm(-2), a V(oc) value of 776?mV, a fill factor (FF) of 0.70 under AM 1.5 illumination (100?mW?cm(-2)). Moreover, the overall efficiency remained at 97% of the initial value after 1000?h of visible-light soaking.     

Computational design of new organic (D–π–A) dyes based on benzothiadiazole for photovoltaic applications,especially dye-sensitized solar cells

Research on Chemical Intermediates - A theoretical study on four organic dyes based on bis(4-hexyloxy)triphenylamine as donor and electron acceptor cyanoacrylic acid with a...     

Compact layer influence on hysteresis effect in organic–inorganic hybrid perovskite solar cells

Organic–inorganic hybrid perovskite solar cells have attracted great attention due to their high power conversion efficiency and low cost. However, an anomalous hysteresis effect exists in the perovskite solar cells, especially with TiO₂ as the n-type electron extraction layer. In this communication, we prepare two kinds of TiO₂ compact layers using Atomic Layer Deposition (ALD) and Spin-Coating (SC) methods and compare their influences on the hysteresis effect. By efficiency comparison and AC impedance spectroscopy study, we find that the thickness and morphology of compact layer have a significant influence on the hysteresis effect. Compared to the SC approach, the ALD prepared compact layer is ultra-thin with uniform morphology and shows small interfacial capacitance and large recombination resistance, meaning reduced interfacial charge accumulation and accelerated electron transport, which would relieve the hysteresis effect.     

Performance of CeO2–TiO2-admixed photoelectrode for natural dye-sensitized solar cell

Extracts from roots of Beta vulgaris were used as natural sensitizers of a wide-bandgap semiconductor (CeO₂–TiO₂) in photoelectrochemical solar cells. The natural dye, adsorbed onto the semiconductor surface, absorbs visible light and promotes electron transfer across the dye/semiconductor interface. We have applied CeO₂–TiO₂ to natural dye sensitizer solar cells as a photoelectrode to reduce the charge recombination rate by providing energy barrier at the interface between the photoanode and electrolyte which offers an improvement of photovoltaic efficiency. Short-circuit current density (J _sc) and open-circuit voltages (V _oc) of 9.0 mA cm^?2 and 680 mV, respectively, were obtained, and an effective energy conversion efficiency of 3.5?% was achieved. This simple and cheap technique of cell preparation opens up a perspective of commercial feasibility for inexpensive and environment-friendly dye cells.     

Investigating the effect of π-configurations and methoxy substitution on donor and π- spacers based dyes for dye-sensitized solar cell applications–computational approach

Research on Chemical Intermediates - Triphenylamine and methoxy substituted triphenylamine-based dyes are examined by density-functional theory and time-dependent density-functional theory. The...     

The design,synthesis, and characterization of D-π-A-π-A type organic dyes as sensitizers for dye-sensitized solar cells (DSSCs)

New D-π-A-π-A type organic dyes were synthesized and characterized as sensitizers for dye-sensitized solar cells (DSSCs). These dyes showed wide absorption spectra (300–625 nm) and high molar extinction coefficients (ε_467 nm = 60,911 M⁻¹ cm⁻¹). As dye sensitizers in DSSC, the D-π-A-π-A dye having a cyanoacrylic acid as an acceptor gave the best cell performance with a short-circuit photocurrent density (J_sc) of 7.14 mA/cm², an open-circuit voltage (V_oc) of 0.62 V, and a fill factor (FF) of 0.72, corresponding to an overall conversion efficiency η of 3.19%.     

2Rotaxane based on terpyridyl bimetal ruthenium complexes and β-cyclodextrin as organic sensitizer for dye-sensitized solar cells

The conjugated carboxy-functionalized terpyridyl bimetal ruthenium complex [(tdctpy)Ru(dctpy-(ph)₄-dctpy)Ru(tdctpy)][PF₆]₄ and [2]rotaxane by self-assembly of [(tdctpy)Ru(dctpy-(ph)₄-dctpy)Ru(tdctpy)][PF₆]₄ with β-cyclodextrin are reported as sensitizer for dye-sensitized solar cells (DSSCs), where tdctpy?=?4′-p-tolyl-4,4″-dicarboxy-2,2′?:?6,2″-terpyridine, dctpy?=?4,4″-dicarboxy-2,2′?:?6,2″-terpyridine and dctpy-(ph)₄-dctpy represents a bridging ligand where two 4,4″-dicarboxy-2,2′?:?6′,2″-terpyridine units are connected through four phenyl spacers in the 4′-position. The DSSCs fabricated utilizing these materials give typical electric power conversion efficiency of 0.013–0.523% under air mass (AM) 1.5, 100?mW?cm^?2 irradiation at room temperature. The terpyridyl bimetal ruthenium complex [(tdctpy)Ru(dctpy-(ph)₄-dctpy)Ru(tdctpy)][PF₆]₄ with conjugated-bridge chains displayed much higher conversion efficiency compared with the carboxy-functionalized terpyridyl monometal ruthenium complex [tdctpy-Ru-(idctpy)][PF₆]₂, where idctpy?=?4′-p-iodophenyl-4,4″-dicarboxy-2,2′?:?6,2″-terpyridine. [2]Rotaxane displayed the highest electric power conversion efficiency of 0.523% when β-cyclodextrin was introduced into the conjugated terpyridyl bimetal ruthenium complex and formed [2]rotaxane.     

Synthesis and photophysical properties of donor–acceptor system based bipyridylporphyrins for dye-sensitized solar cells

Bipyridylporphyrin derivatives possessing a porphyrin moiety as the electron donor and bipyridyl moiety as the electron–acceptor were designed and synthesized for dye-sensitized solar cells(DSSCs). The photophysical and electrochemical properties were investigated by absorption spectrometry and cyclic voltammetry. Density functional theory(DFT) was employed to study electron distribution. From the photovoltaic performance measurements, a maximum conversion efficiency(η) of 0.38% was achieved based on the bipyridylporphyrin ruthenium dye A7(J_(SC)= 1.33 mA/cm~2, V_(OC)= 0.45 V, FF = 0.64) under 1.5 irradiation(100 mW/cm~2).     

Heteroatom substitution-induced asymmetric A–D–A type non-fullerene acceptor for efficient organic solar cells

Research on asymmetric A–D–A structured non-fullerene acceptors has lagged far behind the development of symmetric counterpart. In this contribution, by simply replacing one sulfur atom in indacenodithiophene unit with a selenium atom, an asymmetric building block Se PT and a corresponding asymmetric non-fullerene acceptor Se PT-IN have been developed. Asymmetric Se PT-IN achieved a high efficiency of 10.20% in organic solar cells when blended with PBT1-C, much higher than that of symmetric TPT-IN counterpart(8.91%). Our results demonstrated an effective heteroatom substitution strategy to develop asymmetric A–D–A structured non-fullerene acceptors.     

Thiophene–nitroxide radical as a novel combination of sensitizer–redox mediator for dye-sensitized solar cells

We report a novel combination of organic sensitizer and redox mediator in the electrolyte for dye-sensitized solar cells (DSSCs): a thiophene dye and nitroxide radicals. Nitroxide radicals and their oxidized counterparts of oxoammonium cations show robust reversible redox reactions, thus supporting robust DSSC operations. Moreover, their redox potentials (E _1/2) and thus open-circuit voltages (V _OC) can be tuned further by attached functional groups. Optical and electrochemical characterization reveal that these new combinations exhibit enhanced V _OC and power conversion efficiencies compared to the existing iodine mediator (I⁻/I₃⁻) due to the increased V _OC. Also, the selection of the sensitizer–redox mediator turns out to be critical in the overall cell performance. Indeed, the typical ruthenium dye loses its light absorption capability when it is operated in conjunction with the nitroxide radicals.