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Series of metal-free dyes (OMS4-7) featuring a dibenzofulvene connected with thienyl or furanyl as conjugation bridge, T-shaped diarylamines (diphenylamine or phenyl-1-naphthylamine) as donors and different numbers of cyanoacrylic acid as anchors have been synthesized and applied into dye-sensitized solar cells (DSSCs). The efects of different donors, conjuation segments and number of anchors on optical and photovoltaic properties were investigated through photophysics, electrochemical and photovoltaic measurements. Of the DSSCs, the structure contains mono anchor with thienyl dibenzofulvene linked to diphenylamine, i.e. OMS4-based device exhibited the highest power conversion efficiency (PCE) of 2.42%, a value of Jsc of 6.01 mA cm−2, a Voc of 0.63 V, and a fill factor of 0.63 under 10 mM CDA co-adsorbent and AM 1.5 irradiation. The corresponding device was also conducted with respect to different light intensity such as D65, CWF and TL84. As a result, the cell performance based on TL84 with 2500 lx exhibited the best PCE of 8.78%.

The synthesis, structure, physical properties, and electrocatalytic hydrogen production of tetrathiatetracene ligand based [FeFe]-hydrogenase mimic molecules were investigated. By adjusting the amount of iron, mono- and bis-[FeFe] coordinated complexes 1 and 2 were synthesized. The structures of 1 and 2 were analysed by NMR, IR, and absorption spectroscopies, and cyclic voltammetry and DFT computational analysis. In the DFT electron density maps, the HOMOs and LUMOs were located at tetrathiatetracene units, indicating that these complexes retain mainly acene characteristics. When weak acid Et3NHBF4 was added to CH2Cl2 solutions of 1 or 2, the reduction potential of iron complexes was shifted to more positive values proportional to the concentration of acid. As the acid concentration increased, the current of the reduction wave also increased, indicating the occurrence of a catalytic proton reduction reaction. The bulk electrolysis reaction showed 65.8 TON for 1 and 52.8 TON for 2.

Borane-based complexes have attracted considerable attention as thermally activated delayed fluorescence (TADF) emitters because of their thermal stability, high fluorescence efficiency, and favourable carrier mobility. In this work, we provide a facile way for borylated compounds to enable the spatially adjacent electron donor and acceptor groups to form a near-orthogonal configuration, generating an extremely small energy gap between triplet and singlet excited states (ΔEST, ∼30 meV). We demonstrate here a new series of donor-acceptor-donor borylated compounds using functional acridan derivatives as the electron donors and dimesitylborane as the acceptor moieties, which easily generates an intramolecular charge transfer upon excitation. All compounds achieved strong TADF emission and were used as dopants to fabricate TADF OLEDs. Yellow-emitting devices A and B yielded maximum efficiencies of 7.6% (22.2 cd/A) and 10.1% (32.2 cd/A), respectively. Moreover, the green-emitting device C achieved a maximum efficiency of 19.3% (56.8 cd/A) and subsequently dropped to 18.2% (53.6 cd/A) at luminance levels of 102 cd/m2. Overall, the high electroluminescent (EL) efficiencies, together with mitigated efficiency roll-off, illustrate that these compounds have a high potential for EL applications.

Six novel small molecules containing phenothiazine as the core moiety of p-type materials were synthesized in combination with PC 61 BM or PC 71 BM as n-type materials for bulk heterojunction organic photovoltaic (OPV) cells. Phenothiazine was used as donor building blocks to construct acceptor–donor–acceptor (A–D–A) and A–D–D–A small molecule. We investigated the relationship between the molecular structures, optoelectronic and thermal properties, and their blend film morphologies for OPV applications. We further studied their photophysical properties using a time-dependent density functional theory model and the B3LYP functional. A solution-processed OPV employing PT2-DE combined with the electron acceptor PC 61 BM and additive DIO achieved optimal device performance, with a short-circuit current of 6.3 mA cm −2 , an open-circuit voltage of 770 mV, a fill factor of 0.55, and a corresponding overall conversion efficiency of 2.64%. To the best of our knowledge, this is the best-reported performance of a phenothiazine derivative for OPV application.

A series of Y-shaped sensitizers incorporating quinoxaline or quinoxalinoid moieties were prepared and applied in dye-sensitized solar cells (DSSCs). By the introduction of quinoxalinoid functionalities, the absorption extinction coefficients could be enhanced. The molecular structures were modified by introducing an extra acceptor group (A) between a donor (D) and a π-bridge (D-A-π-A) and also by incorporating electron-donating substituents at various positions of the quinoxalinoid moiety. Some of the dyes and mixtures thereof were found to exhibit good light-harvesting efficiencies under both sunlight and indoor light, with efficiencies up to 7.92 % under one sun (AM 1.5G). When operated under indoor light, the efficiency could be boosted to 27.76, 28.74, and 30.45 % under 600, 1000, 2500 lux illumination, respectively. The best performance could be ascribed partly to an improved dye coverage on the TiO2 surface.

Four novel organic dyes (H-1, H-2, H-3, H-4) containing phenyl-thiophenyl-thiophenyl as a bridge unit were synthesized and effectively used for the fabrication of dye-sensitized solar cells (DSSCs). In both compounds, a triarylamine moiety and cyanoacrylic acid function as an electron donor and an electron acceptor, respectively. H-1 and H-3 exhibited high interaction between lithium ions and [3.3]paracyclophane, resulting in low charge recombination and high open-circuit voltage (Voc). When deoxycholic acid was used as a coadsorbent, the optimal device performance was observed in H-3, involving a short-circuit current of 16.96 mA cm−2, a Voc of 705 mV, and a fill factor of 0.64, which correspond to an overall conversion efficiency of 7.55%. Photophysical properties were analyzed using a time-dependent density functional theory model and the B3LYP functional. Furthermore, the electronic characteristics of the DSSCs were determined using electrochemical impedance spectroscopy and controlled intensity-modulated photospectroscopy.

Herein, eight metal-free organic dyes (YH-1–YH-8) containing olefin or acetylene as π-spacer linkages in a triarylene bridge were synthesised. Moreover, two dyes (1N-PPP and 1N-PPS) without olefin and triple bonds as π-spacer linkages were used as references. The photophysical and electrochemical properties of the dyes were characterised, and the dyes were then used to fabricate dye-sensitised solar cells (DSSCs). We demonstrated the use of a D–π–A dipolar system by employing arylamine derivatives as an electron donor, triarylene with iterative olefin or acetylene as a π-bridge, and cyanoacrylic acid as an electron acceptor. YH-1 had olefin as a repeating unit in the triarylene bridge and exhibited broad absorption, favourable short-circuit photocurrent density (Jsc), and favourable open-circuit voltage (Voc) when used in a film morphology with DCA as a coabsorbent. The optimal device exhibited a Jsc of 16.23 mA cm−2, a Voc of 650 mV, and a fill factor of 0.67, corresponding to an overall conversion efficiency of 7.08%. The photophysical properties of the DSSCs were analysed using time-dependent density functional theory with the B3LYP functional.

Six novel organic dyes (RY1∼RY6) containing spiro[fluorene-9,9′-phenanthren]-10′-one as an auxiliary acceptor were synthesised and effectively used for the fabrication of D-A-π-A type dye-sensitized solar cells (DSSCs). The molecular structures were modified by introducing a novel spiro[fluorene-9,9′-phenanthren]-10′-one auxiliary acceptor group between the donor and the π-bridge. The molecular rigidity can be enhanced by depressing intermolecular aggregation and carbonyl group can trapping the Li+ or I3− ions to retard the charge recombination. The sensitizer RY3 was found to perform remarkable light-harvesting efficiency of 6.30% at AM1.5 solar condition and 21.67% at TL84 (2500 lux) illuminations without DCA co-deposition. For further improvement, a higher efficiency can be achieved through a suitable co-sensitization of N719 and RY3, which displayed an efficiency of 8.55% under one sun (AM 1.5). While operated under indoor light, the efficiency was boosted to 25.57% and 27.04% at 1000 & 2500 lux illuminations, respectively. The high performance of co-sensitization of N719 and RY3 can be ascribed to a high surface coverage and a broader range of absorption wavelength. Stability test of the device co-sensitized with N719 and RY3 showed a mild decay of PCE 3.74% after 96 h, while it retained 84.49% of its original PCE after 336 h in ambient atmosphere without encapsulation.

To obtain a broad spectral response in the visible region, TiO2 film is co-sensitized with a porphyrin dye (FNE57 or FNE59) and an organic dye (FNE46). It is found that the stepwise co-sensitization in one single dye solution followed by in another single dye solution is better than the co-sensitization in a cocktail solution in terms of photovoltaic performance. The stepwise co-sensitization first with a porphyrin dye and then with an organic dye outperforms that in a reverse order. DSSC devices based on co-sensitizers FNE57 + FNE46 and FNE59 + FNE46 with a quasi-solid-state gel electrolyte generate power conversion efficiencies of 7.88% and 8.14%, respectively, which exhibits remarkable efficiency improvements of 61% and 35%, as compared with devices sensitized with the porphyrin dyes FNE57 and FNE59, respectively. Co-sensitization brings about a much improved short-circuit photocurrent due to the complementary absorption of the two sensitizers. The observed enhancement of incident monochromatic photon-to-electron conversion efficiency from individual dye sensitization to co-sensitization is attributed to the improved charge collection efficiency rather than to the light harvesting efficiency. Interestingly, the open-circuit photovoltage for the co-sensitization system comes between the higher voltage for the porphyrin dye (FNE57 or FNE59) and the lower voltage for the organic dye (FNE46), which is well correlated with their electron lifetimes. This finding indicates that not only the spectral complementation but also the electron lifetime should be considered to select dyes for co-sensitization.

Organic dipolar compounds containing a 1,3-indandione-5,6-dicarboxylic acid moiety as an electron acceptor group were examined for the feasibility of using as the light harvesting material in dye-sensitized solar cells. Two compounds with triphenylamine donor moieties were synthesized by attaching it to 1,3-indandione-5,6-dicarboxylic acid. The device made with these simple dyes achieved a quantum yield up to 2.5 %, which is comparable to the widely used dye made with cyanoacrylic acid. The spectroscopic properties of these compounds were analysed with the aid of theoretical models according to the time-dependent density functional theory.

Novel ferrocene–oligothiophenylene–cyanoacrylic acid in the form of donor–spacer–acceptor dyads was synthesized. The compound with a single unit of thiophenylene showed the lowest energy transition in neutral state. For radical cations, the lowest energy transition appears red-shifted along with the increased number of thiophenylene units. These results suggested that the electronic structure of radical cations is significantly different from that of neutral molecules.

Alkoxyphenyl-substituted carbazole-based metal-free organic dyes were synthesized and effectively used for dye-sensitized, visible-light-driven, photocatalytic hydrogen production. Photocatalytic hydrogen production was investigated using a TiO2/dye/Pt structure with triethanolamine as the sacrificial reagent. The dye-loaded TiO2 photocatalyst exhibited a high yield of hydrogen production when the length of the alkoxy chain was long enough to sufficiently improve the hydrophobicity at the interface between the dye-loaded TiO2 and the water medium. In the alkoxyphenyl-substituted carbazole dyes, the dye with the longest alkoxy chain (C22) exhibited the best hydrogen production performance, but it had a yield only slightly better than that of the dye with the second longest chain length (C16). The dye C22 displayed a turnover number (TON) of 3094 after 24 h of visible light irradiation (>420 nm). However, the compound with no hydrophobic substituent (C1), exhibited the lowest hydrogen production performance with a TON of 1497. Thus, a 207% increase in the hydrogen production yield was observed when hydrophobic substituents were present. Analysis of time-resolved absorption spectra, impedance spectra and incident photon conversion efficiency spectra revealed that the alkoxy chain has a hydrophobic effect at the interface between the dye-loaded TiO2 and the water. Specifically, the hydrophobicity of the dye improved the charge-recombination lifetime for electron injection from the dye into the TiO2 surface in the water for hydrogen production.

A series of new pyridomethene–BF2/phenothiazine hybrid metal-free organic sensitizers K1–K8 containing different π-spacers were synthesized and applied in dye-sensitized solar cells (DSSC). The introduction of the pyridomethene–BF2 complex unit to the phenothiazine chromophore resulted in a high molar extinction coefficient in favor of light harvesting. Quantum chemical calculations were performed using the density functional theory (DFT) at the B3LYP/6-31G(d,p) level to investigate the structural properties and electron density distributions of these dyes. The effect of dyes K1–K8 on the performance of DSSC was investigated systematically with comparisons to the plain phenothiazine dyes R1 and R2. Upon co-adsorption with deoxycholic acid, the dye K3, with a thiophene unit between the phenothiazine and pyridomethene–BF2 units, exhibited the best photovoltaic performance. The short-circuit current density (Jsc) was 15.43 mA cm−2 with an open-circuit voltage (Voc) of 0.69 V and a fill factor (FF) of 0.62, which correspond to a power-conversion efficiency (η) of 6.58% under AM 1.5G irradiation (100 mW cm−2). The n-hexyl chain attached to the thiophene in K4–K5 improved the Voc value. The presence of the phenyl pyridomethene–BF2 moiety at the N(10) atom of phenothiazine in K6–K8 reduced π–π aggregation. These results reveal the advantage of incorporating a pyridomethene–BF2 group in the dyes for high-performance DSSC cells.

Novel organic dyes that consist of either a benzo[1,2- b :4,5- b ′]dithiophene or a benzo[1,2- b :4,5- b ′]difuran core exhibited remarkable solar-to-energy conversion efficiency in dye-sensitized solar cells. The planar geometry of bridge moiety and its bulky substituents helped the dyes to form a high quality monolayer on the surface of titanium oxide. A typical device displayed photon-to-current conversion efficiency 60% in the region of 380–575 nm, a short-circuit photocurrent density 13.45 mA cm −2 , an open-circuit photovoltage 0.72 V, and a fill factor 0.63, corresponding to an overall conversion efficiency 6.12%. In a test of using deoxycholic acid as a co-absorbent, an improvement of quantum efficiencies 8.37% was observed for certain compounds. However, for others the quantum efficiency decreased in 6.60–7.91%. The latter result indicated that the quality of some films cannot be further improved by the addition of deoxycholic acid. The photophysical properties were analyzed with the aid of TDDFT.

The effect of switching the phenylene and thiophenylene units in the triarylene bridge of organic donor-bridge-acceptor dyads on the performance of dye-sensitized solar cells is investigated. A thiophenylene group displays several distinctive advantages over those of a phenylene group. The electron-donating nature of thiophenlene elevates the electron energy level of the dyads and narrows down the energy gap of the electronic transition, therefore elongates the absorption wavelength. The presence of thiophenylene unit along the bridge also increases the planarity of the molecular geometry, therefore enhances the degree of π-delocalization; however, it also speeds up the rate of charge recombination. The multiple effects of thiophene group along the bridge are examined systematically on two types of dye derivatives, i.e., the T -series and the M -series dyes. Among all the dyes, the ones containing a phenylene–thiophenylene–thiophenylene bridge (T-PSS) showed the highest performance. A typical device made with T-PSS displayed the maximal monochromatic incident photon-to-current conversion efficiency of 65% in the wavelength region between 350 nm and 515 nm, a short-circuit photocurrent density 15.88 mA cm − 2 , an open-circuit photovoltage 0.64 V, and a fill factor 0.60, that corresponds to an overall conversion efficiency of 6.13%. The packing order of T-PSS can be further improved by adding deoxycholic acid to an overall conversion efficiency of 6.71%.

Organic dyes that consist of an anthracene moiety between a triphenylamine donor group and a cyanoacrylic acid acceptor group displayed remarkable solar-to-energy conversion efficiency in dye-sensitized solar cells. The planar geometry of anthracene and its bulky substituents helped the dyes to form a high quality monolayer on the surface of TiO 2 . A typical device made with the dye AN-Bu displayed a maximal photon-to-current conversion efficiency (IPCE) 65% in the region of 350–510 nm, a short-circuit photocurrent density ( J sc ) 12.78 mA cm −2 , an open-circuit photovoltage ( V oc ) 0.73 V, and a fill factor (FF) 0.67, corresponding to an overall conversion efficiency 6.23%. In an experiment of using deoxycholic acid (DCA) as a co-absorbent, the values of V oc stayed in a similar range, yet the values of J sc were reduced in ca. 11% due to a decrease of loading amounts. This result indicated that the quality of the dye films cannot be further improved by the adding of DCA. The photophysical properties were analyzed with the aid of a time-dependent density functional theory (TDDFT) model with the B3LYP functional.

1,2,3,4-Tetrafluoropentacene is prepared from a soluble precursor containing a carbonyl bridge across the central benzene ring. It underwent dimerization readily in solution, yet displayed a high stability in the solid state. While fabricated into OFET devices, it exhibited an ambipolar charge transport characteristic. Its spectral and electronic properties are described.

The effect of changing substituents of organic dyes for their performance on dye-sensitized solar cells (DSSCs) is examined. These dyes consist of an aromatic amine donor group, a cyanoacrylic acid acceptor group, and a triaryl spacer group, while they are linked together by consecutive palladium catalyzed coupling reactions. These materials exhibit strong charge transfer absorption bands in the UV/vis region. Their redox potential levels were estimated by cyclic voltammetry, and found to suit well to the charge flow in DSSCs. Adding electron-donating substituents on the phenyl groups of aromatic amines increased the electron density on the donor groups, therefore reduced the HOMO/LUMO band gap. These dyes were chemisorbed on the surface of nanocrystalline TiO2, and fabricated into DSSCs through standard operations. For a typical device the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach to 80%, with a short-circuit photocurrent density (Jsc) 16.34 mA cm−2, an open-circuit photovoltage (Voc) 0.68 V, and fill factor (FF) 0.55, which corresponds to an overall conversion efficiency of 6.05%.

A series of organic dipolar compounds containing a donor (D), a bridge (B), and an acceptor (A), forming a D–B–A type of dyads, were synthesized by convenient methods and were utilized successfully on dye-sensitized solar cells. The central bridges were made of three linearly connected arylene groups, i.e., phenylenes or thiophenylenes. The donor groups were aromatic amines, i.e., either a diphenylamine or a naphthylphenylamine group. The acceptor group was a cyanoacrylic acid, which can be anchored onto the surface of TiO2 in a photovoltaic device. These devices performed remarkably well, with a typical quantum efficiency of 5–7%, and optimal incident photon to current conversion efficiency (IPCE) exceeding 80%. The devices made with a naphthylphenylamine donor group performed slightly better than those made with a diphenylamine donor group. Compounds containing a phenylene–thiophenylene–phenylene bridge group performed better than those with other kinds of triarylene linkages. Their photochemical behaviors were analyzed by using time-dependent density functional theory (TDDFT) models with the B3LYP functional.

Organic dyes consisting of a [2.2]paracyclophane unit along the main chromophore are examined for their application in sensitized solar cells. These materials exhibit considerably high values of open-circuit voltage (V(oc)) ranging 0.69-0.72 V, and an overall efficiency up to 3.8%.

A series of organic dyes were prepared that displayed remarkable solar-to-energy conversion efficiencies in dye-sensitized solar cells (DSSCs). These dyes are composed of a 4-tert- butylphenylamine donor group (D), a cyanoacrylic-acid acceptor group (A), and a phenylene-thiophene-phenylene (PSP) spacer group, forming a D-p-A system. A dye containing a bulky tert- butylphenylene-substituted carbazole (CB) donor group showed the highest performance, with an overall conver- sion efficiency of 6.70 %. The perfor- mance of the device was correlated to the structural features of the donor groups; that is, the presence of a tert- butyl group can not only enhance the electron-donating ability of the donor, but can also suppress intermolecular aggregation. A typical device made with the CB-PSP dye afforded a maxi- mum photon-to-current conversion ef- ficiency (IPCE) of 80 % in the region 400-480 nm, a short-circuit photocur- rent density Jsc = 14.63 mA cm 2 ,a n open-circuit photovoltage Voc = 0.685 V, and a fill factor FF = 0.67. When che- nodeoxycholic acid (CDCA) was used as a co-absorbent, the open-circuit volt- age of CB-PSP was elevated signifi- cantly, yet the overall performance de- creased by 16-18 %. This result indicat- ed that the presence of 4-tert-butyl- phenyl substituents can effectively in- hibit self-aggregation, even without CDCA.

A series of organic dyes containing a phenothiazine central unit were synthesized and were used effectively in the fabrication of dye-sensitized solar cells (DSSCs). A cyanoacrylate moiety was added at the C(3) position of the phenothiazine as an electron acceptor, and a triarylamine moiety was attached at the C(7) position as an electron donor. The DSSCs made with these dyes displayed remarkable quantum efficiency, ranging from 4.2–6.2% under an AM 1.5 solar condition (100 mW cm−2). A variety of substituents, i.e., methyl, hexyl and triphenylamino groups, were added at the N(10) of phenothiazine in order to optimize the incident photon-to-current conversion efficiency. Along the main chromophore a thiophenylene group was inserted at different positions to examine its influence on the properties of devices. The best performance was found in compound NSPt-C6, in which a hexyl group was attached at the N(10) of phenothiazine and a thiophenylene at the C(7) position. It displayed a short-circuit current (Jsc) of 14.42 mA cm−2, an open-circuit voltage (Voc) of 0.69 V, and a fill factor (ff) of 0.63, corresponding to an overall conversion efficiency of 6.22%. Their photophysical properties were analyzed with the aid of a time-dependent density functional theory (TDDFT) model with the B3LYP functional. Their photovoltaic behavior was further elucidated by the electrochemical impedance spectroscopy.

A series of organic dyes containing oligo-phenothiazine were synthesized and used effectively on the fabrication of dye-sensitized solar cells (DSSCs). In these compounds the phenothiazine moiety functions both as an electron donor and as a π-bridge. These materials exhibit considerably high values of open-circuit voltage (Voc) ranging from 0.78–0.83 V under an AM1.5 solar condition (100 mW cm−2). Two kinds of substituents, i.e., hexyl and hexyloxyphenyl groups, were added onto the N(10) of phenothiazine for comparison. The best device displayed a short-circuit current (Jsc) of 14.3 mA cm−2, an open-circuit voltage (Voc) of 0.83 V, a fill factor (FF) of 0.65, corresponding to an overall conversion efficiency of 7.78%. Their photophysical properties were analyzed with the aid of a time-dependent density functional theory (TDDFT) model with the B3LYP functional. The electronic nature of the devices was further elucidated by using electrochemical impedance spectroscopy.

A new series of organic dyes containing a triarylamine donor group, a triarylene-linked bridging moiety, and a cyanoacrylic acid acceptor group were synthesized through a simple procedure in high yields. A selected set of substituents were added onto the phenyl group ortho to the cyanoacrylic acid in order to examine their influences on the performance of dye-sensitized solar cells (DSSCs). Their photochemical behaviors were examined under AM1.5 solar condition (100 mW cm−2). A typical device made with a compound containing a -CF3 substituent (PSP-CF3) displayed a short-circuit current (Jsc) 15.16 mA cm−2, an open-circuit voltage (Voc) 0.68 V, a fill factor (ff) 0.68, corresponding to an overall conversion efficiency of 7.0% and a maximal monochromatic incident photon-to-current conversion efficiency (IPCE) 78%. Their photophysical and electrochemical properties were analyzed with the aid of a time-dependent density functional theory (TDDFT) model with the B3LYP functional. Their HOMO and LUMO energy levels are verified by both electrochemical measurements and theoretical calculations.