Search

A series of new dipolar organic dyes containing 9,10-dihydrophenanthrene has been synthesized as sensitizers for the application in dye-sensitized solar cells. These new materials containing less r...

In this study we synthesized three metal-free organic dyes (Cpd11, Cpd16, and Cpd22) featuring 3,4,5-tris(dodecyloxy)phenyl and cyanoacrylic acid moieties as electron-donor and electron-acceptor/anchoring units, respectively, linked through various dithienothiophenyl conjugated spacers. Cpd16 exhibits mesomorphic properties, confirmed through polarizing optical microscopy, differential scanning calorimetry, and X-ray diffraction (XRD), due to the appropriate ratio of the lengths of its flexible chain to its rigid core. Molecular modeling of Cpd16, and its d-spacing determined from XRD data, verified the existence of a tilt angle in the SmC phase. Among these metal-free organic dyes, a dye-sensitized solar cell incorporating Cpd16 exhibited the best performance, presumably because of its better packing and its mesomorphic properties; the power conversion efficiency was 3.72% (Voc=0.58 V; Jsc=9.98 mA cm−2; FF=0.65) under simulated AM 1.5 irradiation (100 mW cm−2).

In this study two series of novel symmetrical acceptor–donor–acceptor organic sensitizers containing 3,6- and 2,7-functionalized carbazole cores, respectively, connected to two anchoring cyanoacrylic acid termini via thienyl linkers were synthesized. The effect of the molecular planarity originating from the 3,6- and 2,7-functionalized carbazole cores on the performance of corresponding solar cells were investigated. Molecular orbital analyses revealed the characteristics of the carbazole-based highest occupied molecular orbitals and acid-based lowest unoccupied molecular orbitals. Time-dependent density functional theory calculations allowed us to assign the electronic transitions (>90%) of the low energy bands. Among these new dyes, the highest power conversion efficiency of 4.82% was obtained in a dye-sensitized solar cell device under standard AM 1.5 sunlight with an open-circuit voltage of 0.61 V, a short-circuit photocurrent density of 12.66 mA cm−2 and a fill factor of 0.62.

This paper reports on the design and synthesis of two new ruthenium dyes [Ru(dcbpy)(potip)(NCS)2] (JF-3, dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine, potip = 2-(4-(10H-phenothiazin-10-yl)-5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline, and [Ru(dcbpy)(dpotip)(NCS)2] (JF-4, dpotip = 2-(4-(N,N-diphenylamino)-5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline) that contain electron-donating phenothiazine-based or N,N-diphenylamino-based ancillary ligands. The ruthenium dye JF-3, in which an excellent electron-donating phenothiazine is incorporated, shows superior DSC performance (9.1%; compared to 8.8% for N3). A comparison of the electron-donating phenothiazine and N,N-diphenylamino groups utilized in the molecular architecture of ruthenium dyes demonstrates that the phenothiazine group efficiently increases the molar extinction coefficient of band II and also broadens that band in the UV-vis absorption spectrum, reduces device resistance, increases electron lifetime, and enhances power-conversion efficiency. This finding not only clarifies the significance of multifunctionalized design in the molecular architecture of ruthenium dyes, but also represents an alternative route for the introduction of an excellent electron-donating group for improving the light-harvesting characteristics of ruthenium dyes as well as DSC performance.

Dipolar compounds containing anthracene-based triarylamine donor and cyanoacrylic acid acceptor were synthesized and characterized by electro-optical measurements. The optical spectra of the dyes are dominated by a charge transfer transition. This band is red-shifted and increased in intensity on elongation of conjugation by the introduction of bithiophene or dithienylbenzothiadiazole moiety. Similarly, the oxidation potentials of the dyes are shifted anodically on extension of the conjugation attributable to the reduction in the interaction between the triarylamine and acceptor segments. Theoretical calculations revealed the charge transfer to occur between anthracene and triarylamine moieties. However, in the benzothiadiazole containing dye the charge transfer is observed between the amine and the acceptor segment. Dye-sensitized solar cells fabricated using these dyes showed moderate efficiency which is highly dependent on the nature of the conjugation bridge.

We have synthesized and characterized donor–π–spacer–acceptor type molecules in which 1,3,4-oxadiazoles are π-spacers, triphenylamines are the donors and cyanoacetic acid are the acceptors for use as sensitizers in dye-sensitized solar cells (DSSCs). Detailed absorption, emission, electrochemical, photoelectrochemical and computational studies have been carried out on five novel derivatives. The dyes have an absorption range of 377–388 nm, and an emission in the range of 494–540 nm. There is a large charge transfer from the donor side to the acceptor side on excitation. The propeller shape of the triphenylamine and the bulky substituents on it help in reducing the dye-aggregation on TiO 2 surface. The dyes exhibited good overall conversion efficiency (2.79–3.21%). Plane wave calculations indicate that the dye has a reasonably strong binding to the TiO 2 surface and the generated DOS picture shows an overlap of the molecular orbitals of the dye and the TiO 2 bands. We conclude that the dyes have a promising role as sensitizers in DSSC.

A stepwise co-sensitization of a TiO 2 mesoporous film in conjunction with two dye molecules, using different sequences of adsorption for achieving a complementary spectral characteristic, is investigated for application to a low-temperature fabrication plastic dye-sensitized solar cell (plastic DSSCs). The stepwise co-sensitization by monomolecular adsorption of N719 / FL and black dye / FL show enhanced photovoltaic performances for the pertinent plastic DSSCs, compare with that of the cell with the corresponding individual dyes. The optimal conversion efficiencies of plastic DSSCs with N719 / FL and black dye / FL are found to be 5.10% and 3.78%, respectively, which are higher than those of the cells with the corresponding individual sensitizers. The incident photon-to-current conversion efficiency (IPCE) and electrochemical impedance spectroscopy (EIS) are also used to analysis these behaviors.

Four novel symmetrical organic dyes (S1–S4) configured with acceptor–donor–acceptor (A–D–A) structures containing electron donating fluorene (S1 and S2) and N-alkyl dithieno[3,2-b:2′,3′-d]pyrrole (DTP) (S3 and S4) cores terminated with two anchoring cyanoacrylic acids (as electron acceptors) were synthesized and applied to dye-sensitized solar cells (DSSCs). The DSSC device based on S2 dye showed the best photovoltaic performance among S1–S4 dyes: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 76%, a short circuit current (JSC) of 12.27 mA/cm2, an open circuit voltage (VOC) of 0.61 V, a fill factor (FF) of 0.63, and an overall power conversion efficiency (η) of 4.73%. Besides, the utilization of chenodoxycholic acid (CDCA) as a co-adsorbent in the DSSC device based on S3 dye showed a significant improvement in its η value (from 3.70% to 4.31%), which is attributed to the suppression of dye aggregation on TiO2 surface and thus to increase the JSC value eventually.

The synthesis, electronic properties, and performance in dye-sensitized solar cells (DSSCs) of four cone-shaped organic dyes (ITD, ITD-Th, ITD-Hx, and ITD-OM) containing the isotruxene π-scaffold are reported. Selective substitution of the unsymmetrical isotruxene core with two diarylamino donors and one cyanocarboxylic acid acceptor was achieved by using a prefunctionalized dibromoisotruxene building block. The ortho-para-branched isotruxene core allows strong electronic couplings among the donors and the acceptor, leading to red-shifted absorption profiles with significant charge-transfer character. All four isotruxene dyes display reversible anodic waves in cyclic voltammagrams with both HOMO and LUMO potentials suitable for application in DSSCs. The DSSCs fabricated with these cone-shaped organic dyes exhibited high open-circuit voltages (0.67-0.76 V) and fill factors (0.67-0.72) with a power conversion efficiency (η) up to 5.45%, which is 80% of the ruthenium dye N719-based standard cell fabricated and measured under the same conditions.

A series of donor-pi-acceptor-type organic dyes based on 1-alkyl-1H-imidazole spacers 1-5 have been developed and characterized. The two electron donors are at positions 4 and 5 of the imidazole, while the electron-accepting cyanoacrylic acid is incorporated at position 2 by a spacer-containing heteroaromatic rings, such as thiophene and thiazole. Detailed investigation on the relationship between the structure, spectral and electrochemical properties, and performance of DSSC is described here. Dye-sensitized solar cells (DSSCs) using dyes as the sensitizers exhibit good efficiencies, ranging from 3.06 to 6.35 %, which reached 42-87 % with respect to that of N719-based device (7.33 %) fabricated and measured under similar conditions. Time-dependent density functional theory (TDDFT) calculations have been performed on the dyes, and the results show that both electron donors can contribute to electron injection upon photo-excitation, either directly or indirectly by internal conversion to the lowest excited state.

A series of electroluminescent copolymers containing fluorene-2,8-disubstituted dibenzothiophene ( PFD ), fluorene-2,8-disubstituted dibenzothiophene- S , S -dioxide ( PFDo ) and phosphorescent benzimidazole-based iridium (Ir) complexes in the backbones were synthesized by the Suzuki coupling reaction. The thermal stabilities, HOMO/LUMO levels and triplet energy gap ( E T ) values were enhanced with increasing contents of dibenzothiophene ( D ) or dibenzothiophene- S , S -dioxide ( Do ) segments in the copolymers. The relative intensities of phosphorescence and fluorescence were affected by the energy transfer and back transfer efficiencies between the polymer backbones and iridium units as evidenced by solid state PL and EL spectra. PLED devices with a configuration of ITO/PEDOT:PSS (50 nm)/metal-free copolymers ( P1 – P5 ), Ir-copolymers ( P7 – P13 ) and Ir-doped copolymers ( P3 doped with Ir-complexes 6 and 8 ) (60–80 nm)/TPBI (40 nm)/LiF (1 nm)/Al (120 nm) were fabricated, and the electroluminescence (EL) efficiencies depended on the chemical constituents and triplet energies of the copolymers. The space-charge-limited current (SCLC) flow technique was used to measure the charge carrier mobilities of these copolymers, where both hole and electron mobilities were in the following order: the metal-free copolymers ( P2 , P3 and P5 ) > Ir-doped copolymers ( P3 + 3 or 10 mol% Ir-complex 6 ) > Ir-copolymers ( P7 , P8 , P12 and P13 ).

New dipolar dyes featuring arylamine donors, fluorene or biphenyl conjugation, and cyanoacetic acid acceptor units have been synthesized and characterized by spectral, optical, and electrochemical measurements. Absorption measurements indicate that the fluorene conjugation is beneficial for red shifting the charge transfer transition and increasing the optical density. On the contrary, the biphenyl linker leads to a blue-shifted hypochromic charge-transfer transition due to the inefficiency in the π-conjugation. For a particular linker, the diphenylamine unit acts as an efficient donor when compared to the 1-naphthylphenylamine moiety. However, the red shift observed in the absorption profile for the diphenylamine-containing dyes is compensated for by a reduction in the molar extinction coefficient, that is, the naphthylamine derivatives are beneficial for increasing the molar extinction coefficient. Electrochemical investigations show that the fluorene-based dyes are more redox stable than the correspond...

Six novel conjugated copolymers (P1−P6) containing coplanar cyclopentadithiophene (CPDT) units (incorporated with bithiazole/thienyl-based monomers) were synthesized and developed for the applications of polymer solar cells (PSCs). Copolymers P1−P6 covered broad absorption ranges from UV to near-infrared (400−800 nm) with narrow optical band gaps of 1.70−1.94 eV, which are compatible with the maximum solar photon reflux. Partially reversible p- and n-doping processes of P1−P6 in electrochemical experiments were observed. Compared with those previously reported CPDT-based narrow band gap polymers, the proper molecular design for HOMO/LUMO levels of P1−P6 induced relatively high photovoltaic open-circuit voltages in the PSC devices. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed highly self-assembled π−π stackings. Under 100 mW/cm2 of AM 1.5 white-light illumination, bulk heterojunction PSC devices containing an active layer of electron donor copolymers P1−P6 blended with ele...

Five novel conjugated copolymers (P1-P5) containing coplanar cyclopen- tadithiophene (CPDT) units (incorporated with arylcyanovinyl and keto groups in dif- ferent molar ratios) were synthesized and developed for the applications of polymer solar cells (PSCs). Polymers P1-P5 covered broad absorption ranges from UV to near infrared (400-900 nm) with narrow optical band gaps of 1.38-1.70 eV, which are compatible with the maximum solar photon reflux. Partially reversible p- and n- doping processes of P1-P5 in electrochemical experiments were observed, and the proper molecular design for highest occupied molecular orbital (HOMO)/lowest unoc- cupied molecular orbital (LUMO) levels of P1-P5 induced the highest photovoltaic open-circuit voltage in the PSC devices, compared with those previously reported CPDT-based narrow-band-gap polymers. Powder X-ray diffraction (XRD) analyses suggested that these copolymers formed self-assembled p-p stacking and pseudobilay- ered structures. Under 100 mW/cm 2 of AM 1.5 white-light illumination, bulk hetero- junction PSC devices containing an active layer of electron donor polymers P1-P5 mixed with electron acceptor (6,6)-phenyl C61 butyric acid methyl ester (PCBM) in the weight ratio of 1:4 were investigated. The PSC device containing P1 gave the best preliminary result with an open-circuit voltage of 0.84 V, a short-circuit current of 2.36 mA/cm 2 , and a fill factor of 0.38, offering an overall power conversion effi- ciency (PCE) of 0.77% as well as a maximal quantum efficiency of 23% from the

Series of dyes containing a cyanovinyl entity in the spacer have been developed and characterized. Dye-sensitized solar cells (DSSCs) using the dyes as the sensitizers exhibited good efficiencies ranging from 3.48−4.92%, which reached 45−70% with respect to that of an N719-based device fabricated under similar conditions. In general, better DSSC performances are observed with molecules having a shorter distance between the internal cyanovinyl entity and the amine donor. Computational analysis indicated that the cyanovinyl entity may behave as a charge trap, especially in the long molecules studied, where the cyanovinyl group is away from the electron-donating amine by two or more aromatic groups. A positive correlation is observed between the theoretically calculated product of oscillator strengths and the charge shift at the cyanoacrylic acid group and the measured short-circuit current in DSSCs. Therefore, it is likely that the charge-trapping in the cyanovinyl entity reduces the electronic interaction ...

New organic dyes that contain variable lengths of conjugation, featuring oligothiophene and arylamines at the 2- and 3-position, have been synthesized. These compounds are characterized by photophysical, electrochemical, and theoretical computational methods. Nanocrystalline TiO2-based dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers. The overall efficiencies of the sensitized cells range from 4.11 to 6.15%, compared to a cis-di(thiocyanato)-bis(2,2′-bipyridyl)-4,4′-dicarboxylate ruthenium(II)-sensitized device (7.86%) fabricated and measured under similar conditions. The devices made from these compounds have higher open-circuit voltage (VOC) compared to oligothiophene congeners with arylamines at the 2-position only. The hydrophobic segment at the 3-position appears to help retarding the charge transfer from the conduction band of TiO2 to the electrolyte, I3−. Supplementary studies of the transient photovoltage and electrochemical impedance are in support ...

Series of dyes based on 1H-phenanthro[9,10-d]imidazole chromophores were developed and characterized. Dye-sensitized solar cells (DSSCs) using the dyes as the sensitizers exhibited good efficiencies, ranging from 2.95 to 4.68%, which reached 45−70% with respect to that of an N719-based device fabricated under similar conditions. Incorporation of arylamine moieties at 1H-phenanthro[9,10-d]imidazole was found to retard charge recombination of the electrons in the conduction band of TiO2 with the oxidized dyes. In contrast, incorporation of hydrophobic dodecanyl chains at 1H-phenanthro[9,10-d]imidazole reduced the dark current and improved the device efficiency. Results of TDDFT computation on the compounds are in support of the charge-transfer character of the compounds and consistent with the device performance. A cascade of charge separation is possible for compounds with arylamine moieties via an internal conversion from a bright higher excited state to a long-range charge separated state. Our results in...

The effects of hydrothermal temperature on the preparation of TiO2 colloids, and their film thickness on fluorine-doped tin oxide (FTO) glass, toward the performance of a dye-sensitized solar cell (DSSC) were investigated. Pore diameter and surface area of the TiO2 are of paramount importance in determining the cell efficiency. With the increase of hydrothermal temperature, the pore diameter increases linearly; however, the surface area shows the reverse effect. It is found that the DSSC assembled with the TiO2 films prepared under the hydrothermal temperature of 2401C, and the film thickness larger than 10mm gives optimal performance. The effect of film thickness of TiO2 on the performance of the DSSC can be explained by the relative size of reactive species diffusing into the thin film and the lifetime of injected electrons. Electrochemical impedance spectroscopy (EIS) was also used to analyze the resistance of the cell, developed as a result of the change in the thickness of the TiO2 thin film. The at-rest stability for over 200 days was monitored and the results show that the solar energy conversion efficiency was found to decrease from 5.0% of initial value to 3.0% at the end. r 2006 Elsevier B.V. All rights reserved.

Silica−titania-based organic−inorganic hybrid materials (OIHMs) containing covalently bonded organic chromophores with photosensitization ability were developed. The presence of the Ti−O−Si linkage in these OIHMs was established by infrared spectroscopy. Photocurrent and photovoltage were generated upon irradiation of these OIHM films on an indium tin oxide (ITO) glass or nanocrystalline TiO2 surface. The photovoltaic properties depend on the relative molar fractions of silica and titania in the OIHM films. The OIHMs thus prepared can serve as anchoring matrixes for associating the chromophores with nanocrystalline TiO2 surfaces and can be used as active layers in photovoltaic devices. Control experiments using a blending protocol suggest that covalent bonding between the chromophores and the silica−titania hybrid networks is essential to enhancing the performance of photovoltaic devices.

Ruthenium(II) complexes with new phenanthrenyl ligand (TAPNB) have been synthesized and examined. The spectroscopic and electrochemical measurements showed that the excited states of those complexes matched the conduction band of titanium dioxide. The overall power conversion efficiencies of the solar cells utilized these new complexes as sensitizers for TiO 2 films were less than that of N3-sensitized cell. Although the open-circuit voltage was similar to that of N3-sensitized cell, the short-circuit current was ∼one order lower. Such outcome may be attributed to the less amount of dyes adsorbed due to the steric congestion of the complex. When NCS ligand was replaced by pyridyl ligand, the energy of metal-to-ligand charge transfer (Ru(II)→TAPNB) increased and resulted in blue shift of the absorption band. Anchoring of carboxylic acid at the surface of TiO 2 slightly lowered the energy of Ru(II)→TAPNB charge transfer band. As carboxylic acid anchor was replaced by acetyl ester, the weaker interaction between the semiconductor and the ligand led to diminishing amount of the complex adsorbed and less photocurrent was detected.

Versatile dyes based on benzothiadiazole and benzoselenadiazole chromophores have been developed that perform efficiently in dye-sensitized solar cells. Power conversion efficiency of 3.77% is realized for a dye in which charge recombination is probably hindered by the nonplanar charge-separated structure.

Electrochromic (EC) behaviors of 1,1′-diheptyl-4,4′-bipyridinium (heptyl viologen; HV) and N,N,N′,N′-tetramethyl-1,4-phenylenediamine (TMPD) were studied spectroelectrochemically. Suitable darkening potentials for HV and TMPD were determined to be −1.3 and −0.3 V (vs. Ag/AgClO4), respectively, according to voltammetric and spectroelectrochemical measurements. A solution-phase electrochromic device (ECD) was fabricated by sandwiching both HV and TMPD in between two parallel indium tin oxide (ITO) electrodes with an intervening space. The influences of the applied voltage and the cell gap on the single-compartment ECD performance are discussed. The transmittance transients measured at 615 nm suggest that there is no need to darken the ECD beyond 1.0 V, while the ECD can be bleached at 0 V. Self-bleaching was possible with an open circuit. At 615 nm, a typical transmittance change of over 75% was observed. The reversible electrochromism was achieved only when the cell gap was maintained at 0.28 mm or less. Once reversible operating conditions were maintained, a coloration efficiency of 169 cm2/C at 615 nm for the ECD was obtained.

Metal-free dyes (BP-1 to BP-3) containing a 9,10-dihydrophenanthrene unit in the spacer have been synthesized. The dye with the highest cell efficiency, BP-2, was used in combination with SQ2 for cosensitized DSSCs. The cosensitized DSSC in which the ratio of BP-2 and SQ2 is 8:2 (v/v) has a record high efficiency of 8.14% among cosensitized systems using all metal-free sensitizers. Dye distribution along the TiO2 film depth was analyzed by an Auger electron spectroscopy technique.

A new series of amphiphilic heteroleptic ruthenium(II) sensitizers with a fluorous bis-ponytailed bipyridine ancillary ligand, [Ru(H(2)dcbpy)(4,4'-bis(R(f)CH(2)OCH(2))-2,2'-bpy)(NCS)(2)] [where R(f) = HCF(2)CF(2) (CT4), C(3)F(7) (CT7), and HCF(2)CF(2)CF(2)CF(2) (CT8)], have been synthesized and fully characterized by UV/vis, visible emission, NMR, fast atom bombardment mass spectrometry, and cyclic voltammetric studies. Dye-sensitized solar cells (DSCs) based on these dyes exhibit efficiencies comparable with that of the standard cell based on N719. The conversion efficiency of a CT7- or CT8-based DSC is ~9% higher than that of Z907 with a nonfluorous bis-ponytailed bipyridine ancillary ligand. The fluorous chains were found to increase the dye density on TiO(2) and to help to suppress the dye desorption.

New heteroleptic ruthenium complexes have been synthesized and used as the sensitizers for dye-sensitized solar cells (DSSCs). The ancillary bipyridine ligand contains rigid aromatic segments (fluorene-, carbazole-, or dithieno[3,2-b:2',3'-d]pyrrole-substituted bipyridine) tethered with a hydrophobic hexyl substituent. The conjugated aromatic segment results in significant bathochromic shift and hyperchromic effects in these complexes compared with Z907 (cis-[RuLL'(NCS)(2)]; L=4,4'-dicarboxylic acid-2,2'-bipyridine, L'=4,4'-dinonyl-2,2'- bipyridine). The long hydrocarbon chains help to suppress the dark current if appropriately disposed. DSSCs that use these complexes exhibit very impressive conversion efficiencies (5.94 to 6.91 %) that surpass that of Z907-based (6.36 %) DSSCs and are comparable with that of N719-based standard cells (7.13 %; N719=cis-di(thiocyanato)bis(2,2'-bipyridyl-4,4'-dicarboxylato)ruthenium(II) bis(tetrabutylammonium)) fabricated and measured under similar conditions (active area: 0.5×0.5 cm(2); AM 1.5 sunlight).

A detailed study of the synthesis and photophysical properties of a new series of dipolar organic photosensitizers that feature a 1,3-cyclohexadiene moiety integrated into the π-conjugated structural backbone has been carried out. Dye-sensitized solar cells (DSSCs) based on these structurally simple dyes have shown appreciable photo-to-electrical energy conversion efficiency, with the highest one up to 4.03 %. Solvent-dependent fluorescence studies along with the observation of dual emission on dye 4 b and single emission on dyes 4 a and 32 suggest that dye 4 b possesses a highly polar emissive excited state located at a lower-energy position than at the normal emissive excited state. A detailed photophysical investigation in conjunction with computational studies confirmed the twisted intramolecular charge-transfer (TICT) state to be the lowest emissive excited state for dye 4 b in polar solvents. The relaxation from higher-charge-injection excited states to the lowest TICT state renders the back-electron transfer process a forbidden one and significantly retards the charge recombination to boost the photocurrent. The electrochemical impedance under illumination and transient photovoltage decay studies showed smaller charge resistance and longer electron lifetime in 4 b-based DSSC compared to the DSSCs with reference dyes 4 a and 32, which further illustrates the positive influence of the TICT state on the performance of DSSCs.

A novel series of dipolar organic dyes containing diarylamine as the electron donor, 2-cyanoacrylic acid as the electron acceptor, and fluorene and a heteroaromatic ring as the conjugating bridge have been developed and characterized. These metal-free dyes exhibited very high molar extinction coefficients in the electronic absorption spectra and have been successfully fabricated as efficient nanocrystalline TiO(2) dye-sensitized solar cells (DSSCs). The solar-energy-to-electricity conversion efficiencies of DSSCs ranged from 4.92 to 6.88%, which reached 68-96% of a standard device of N719 fabricated and measured under the same conditions. With a TiO(2) film thickness of 6 microm, DSSCs based on these dyes had photocurrents surpassing that of the N719-based device. DFT computation results on these dyes also provide detailed structural information in connection with their high cell performance.

New dipolar compounds incorporating a dithieno[3,2-b:2',3'-d]thiophene unit as the electron donor, an oligothiophene moiety as the conjugated spacer, and 2-cyanoacrylic acid as the electron acceptor have been synthesized. These nonarylamine type metal-free organic compounds have been successfully used as the sensitizers of dye-sensitized solar cells (DSSCs). The conversion efficiencies of the DSSCs range from 3.54 to 5.15% under AM 1.5 G irradiation. The best efficiency reached approximately 70% of the ruthenium dye N719-based standard cell fabricated and measured under similar conditions.

Two isomeric compounds (1 and 2) containing a dibenzo[f,h]thieno[3,4-b]quinoxaline core and two peripheral arylamines were synthesized. Solution-processed bulk heterojunction (BHJ) solar cells based on these sensitizers and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are reported. The cell fabricated from 1/67 wt % of PCBM exhibited a high power conversion efficiency of 1.70% and an external quantum yield of 55%. The film of the cell was found to have balanced electron and hole mobility and good film morphology.

New metal-free dyes with a furan moiety in the conjugated spacer between the arylamine donor and the 2-cyanoacrylic acid acceptor have been synthesized, and high efficiency dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers.

A series of structurally simple dipolar light-harvesting organic dyes featuring 1,3-cyclohexadiene in the aromatic pi framework for dye-sensitized solar cells has been synthesized and characterized. The highest conversion efficiency of the DSSCs based on these dyes can reach up to 4.4%.

New organic dyes that contain variable lengths of conjugation featuring alternating thiophene and fluorene segments have been synthesized and efficient nano-crystalline TiO2 based dye-sensitized solar cells were fabricated using these molecules as light-harvesting sensitizers.

Two ruthenium sensitizers, [Ru(dcbpy)(opip)(NCS)2] (JF-1, dcbpy = 4,4′-dicarboxylic acid-2,2′-bipyridine, opip = 2-(4-octylphenyl)-1H-imidazo[4,5-f][1,10]phenanthroline) and [Ru(dcbpy)(otip)(NCS)2] (JF-2, otip = 2-(5-octylthiophen-2-yl)-1H-imidazo[4,5-f][1,10]phenanthroline), with unusually high power-conversion efficiency in comparison with other ruthenium complexes containing 1,10-phenanthroline-based ligands were designed. The power-conversion efficiency of JF-2 is 20% higher than that of JF-1, due to the modification of the ancillary ligand with a thiophene moiety. The origins of this device performance diversity are illustrated by photophysical properties, electrochemical data and density functional theory (DFT) studies. The greater device performance of JF-2 compared to JF-1 was caused from the broader MLCT distribution, the appropriate localization of the frontier orbitals and the stronger driving force of the charge injection and regeneration.