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%.     

Novel organic dyes containing bis-dimethylfluorenyl amino benzo[b]thiophene for highly efficient dye-sensitized solar cell

Novel organic dyes, JK-16 and JK-17 containing bis-dimethylfluorenyl amino benzo[b]thiophene are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-16 sensitized cell gave a short circuit photocurrent density (J_sc) of 15.33 mA cm⁻², open circuit voltage (V_oc) of 0.74 V, and a fill factor of 0.66, corresponding to an overall conversion efficiency η of 7.43%, and the JK-17 sensitized cell gave a J_sc of 12.66 mA cm⁻², V_oc of 0.67 V, and a fill factor of 0.65, corresponding to an overall conversion efficiency η of 5.49%.     

Anthracene based organic dipolar compounds for sensitized solar cells

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 TiO₂. 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.     

Metal-free organic dyes with benzothiadiazole as an internal acceptor for dye-sensitized solar cells

We synthesized three metal-free organic dyes (H11–H13) consisting of a 3,6-disubstituted carbazole, benzothiadiazole, and cyanoacrylic acid. All the dyes exhibited high molar extinction coefficients and suitable energy levels for electron transfer from the electrolyte to the TiO₂ nanoparticles. Under standard AM 1.5G solar irradiation, the device using dye H13 with co-adsorbed chenodeoxycholic acid (CDCA) displayed the best performance: an open-circuit voltage (V_oc) of 0.71 V, a short-circuit current density (J_sc) of 12.69 mA cm⁻², a fill factor (FF) of 0.71, and a power conversion efficiency (PCE) of 6.32%. The PCE was ∼79% of that for commercially available N719 cells (8.02%) under the same conditions.     

Organic dyes with a novel anchoring group for dye-sensitized solar cell applications

Two novel trialkylsilyl-containing organic sensitizers (JK-53 and JK-54) have been designed and synthesized. Nanocrystalline TiO₂–silica-based dye-sensitized solar cells (DSSCs) were fabricated using these dyes. Under standard global AM 1.5 solar conditions, the JK-53-sensitized cell gave a short-circuit photocurrent density (J_sc) of 6.37 mA cm^?2, an open-circuit voltage (V_oc) of 0.70 V, and a fill factor of 0.74. These values correspond to an overall conversion efficiency (η) of 3.31%. By comparison, the JK-54-sensitized cell resulted in a J_sc of 7.52 mA cm^?2, a V_oc of 0.71 V, and a fill factor of 0.75. These values give an overall conversion efficiency of 4.01%.     

Synthesis of sensitizers containing donor cascade of triarylamine and dimethylarylamine moieties for dye-sensitized solar cells

Four triarylamine derivatives (XS6-9) containing N,N-dimethylaryl amine units as secondary electron-donating groups are designed and synthesized. These dyes were applied into nanocrystalline TiO₂ dye-sensitized solar cells through standard operations. For a typical device the maximal monochromatic incident photon-to-current conversion efficiency (IPCE) can reach 93%, with a short-circuit photocurrent density (J_sc) 10.8 mA cm⁻², an open-circuit photovoltage (V_oc) 690 mV, and fill factor (FF) 0.61, which corresponds to an overall conversion efficiency of 4.54%.     

Molecular engineering of organic sensitizers containing indole moiety for dye-sensitized solar cells

Three organic dyes, JK-77, JK-78, and JK-79 containing indole unit are designed and synthesized. Nanocrystalline TiO₂ dye-sensitized solar cells were fabricated using these dyes. Under standard global AM 1.5 solar condition, the JK-79 sensitized solar cell gave a short circuit photocurrent density of 13.62 mA cm⁻², open-circuit voltage of 0.705 V, and a fill factor of 0.74, corresponding to an overall conversion efficiency η of 7.18%. We found that the η of JK-79 was higher than those of other two cells due to the higher V_oc. The improved V_oc value is attributed to the suppression of dark current owing to the blocking effect of a long alkyl chain.     

Molecular engineering of organic dyes containing N-aryl carbazole moiety for solar cell

Organic dyes containing N-aryl carbazole moiety are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-25 sensitized cell gave a short circuit photocurrent density (J_sc) of 11.50 mA cm⁻², an open circuit voltage (V_oc) of 0.68 V, a fill factor of 0.66, corresponding to an overall conversion efficiency η of 5.15%, and the maximum incident monochromatic photon-to-current conversion efficiency (IPCE) of 77% at 430 nm.     

Triaryl linked donor acceptor dyads for high-performance dye-sensitized solar cells

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 (J_sc) 16.34 mA cm⁻², an open-circuit photovoltage (V_oc) 0.68 V, and fill factor (FF) 0.55, which corresponds to an overall conversion efficiency of 6.05%.     

Novel organic sensitizers containing a bulky spirobifluorene unit for solar cell

Three organic sensitizers JK-87, JK-88, and JK-89 containing a bulky spirobifluorene unit in the bridged group are designed and synthesized. Under standard global A.M. 1.5 solar condition, the JK-89 sensitized cell gave a short-circuit photocurrent density (J_sc) of 13.02 mA cm⁻², an open-circuit voltage (V_oc) of 0.75 V, and a fill factor of 0.70, corresponding to an overall conversion efficiency η of 6.83%. The η of JK-89 is higher than those of other two cells due to the larger J_sc. The improved J_sc value is mainly attributed to the broad and red-shifted absorption band.     

Synthesis and photovoltaic properties of novel organic sensitizers containing indolo[1,2-f]phenanthridine for solar cell

Organic dyes containing indolo[1,2-f]phenanthridine unit are a promising new class of sensitizers for dye-sensitized solar cells, as a result of their broad and intense visible absorptions. Under standard global AM 1.5 solar condition, the JK-61 sensitized cell gave a short circuit photocurrent density (J_sc) of 15.81 mA cm⁻², an open circuit voltage (V_oc) of 0.73 V, a fill factor of 0.72, corresponding to an overall conversion efficiency of 8.34%.     

Fluorenylvinylenes bridged triphenylamine-based dyes with enhanced performance in dye-sensitized solar cells

We have synthesized a series of new dipolar organic dyes Bn (n=0, 1, 2) employing triarylamine as the electron-donor, 2-cyanoacrylic acid as the electron-acceptor, and fluorenevinylene as the conjugated bridge, which were used as sensitizers in dye-sensitized solar cells. It is found that the solar-energy-to-electricity conversion efficiencies of the prepared DSSCs are in the range of 2.79-5.56%, which reach 35-70% of a standard device based on N719 fabricated and measured under the same conditions. The DSSC sensitized with B1 with balanced length of conjugated bridge shows the highest photo-to-electrical energy conversion efficiency and the open-circuit photovoltage (V_oc) of 0.86 V.     

Synthesis of conjugated organic dyes containing alkyl substituted thiophene for solar cell

Three organic dyes, JK-41, JK-42, and JK-43 containing bis-dimethylfluoreneaniline and alkyl substituted thiophene unit are designed and synthesized. Under standard global AM 1.5 solar condition, the JK-41 sensitized cell gave a short circuit photocurrent density (J_sc) of 15.23 mA cm⁻², open circuit voltage (V_oc) of 0.67 V, and a fill factor of 0.67, corresponding to an overall conversion efficiency η of 7.69%. Molecular-orbital calculations of the three dyes suggest that the electron distribution moves from the aniline derivative to the cyanoacrylic acid moiety. We found that the power conversion efficiency was shown to be quite sensitive to the structural variations of alkyl substituted thiophene moiety.     

Novel iridium complex with carboxyl pyridyl ligand for dye-sensitized solar cells: High fluorescence intensity, high electron injection efficiency?

Novel iridium-based sensitizers Iridium(III) bis[2-phenylpyridinato-N,C^2′]-5-carboxylpicolinate) (Ir1), Iridium(III) bis[2-(naphthalen-1-yl) pyridinato-N,C^2′]-5-carboxyl-picolinate) (Ir2), Iridium(III) bis[2-phenylpyridinato-N,C^2′]-4,4′-(dicarboxylicacid)-2,2′-bipyridine (Ir3) were synthesized for sensitization of mesoscopic titanium dioxide injection solar cells. By changing the ligand, the absorption spectra can be extended and molar extinction coefficient was enhanced. The dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs) based on dye Ir3 showed the best photovoltaic performance: a maximum monochromatic incident photon-to-current conversion efficiency (IPCE) of 85%, a short-circuit photocurrent density (J_sc) of 9.59 mA cm⁻², an open-circuit photovoltage (V_oc) of 0.552 V, and a fill factor (ff) of 0.54, corresponding to an overall conversion efficiency of 2.86% under AM 1.5 sun light. Moreover, the HOMO and LUMO energy levels tuning can be conveniently accomplished by alternating the ligand. The high oxidative potential of Ir3 enables it to be used along with redox electrolyte and the photovoltage was found to be enhanced greatly.     

Effects of Nanocrystalline Porous TiO2 Films on Interface Adsorption of Phthalocyanines and Polymer Electrolytes in Dye-Sensitized Solar Cells

Summary: We have synthesized three kinds of titanylphthalocyanines with different crystal structures (TiOPcs; PcT2000R, PcT3000R, and PcT1100S) and analyzed their crystal structure by X-ray Diffraction (XRD), Fourier transfer IR (FT-IR) spectroscopy, and Transmission Electron Microscope (TEM). From experimental results, we have confirmed that PcT2000R was estimated to be alpha-form; PcT3000R was beta-form, and PcT1100S was gamma-form. Quasi-solid state dye-sensitized solar cell (DSSC) devices were prepared with a polymer electrolyte using TiOPcs as a co-adsorbent. The DSSC device using TiOPc has higher power conversion efficiency than without TiOPc, due to decrease of electron transfer distance by the interface adsorption between TiO₂ film and polymer electrolyte. Also, we have studied the effects of the crystal structures of TiOPcs on the property of polymer electrolyte and the performance of the DSSC device. The best result on power conversion efficiency was 7.13% in DSSC device using PcT3000R having its highest stability. The open-circuit voltage (V_oc) was 0.69 V, the short-circuit current density (J_sc) was 20.02 mA/cm², and the Fill Factor (FF) was 0.52. the addition of TiOPc as co-adsorbent is useful for improve to the performances of DSSC devices such as V_oc, J_sc, and power conversion efficiency.     

Synthesis and photovoltaic properties of fluorene-based copolymers with narrow band-gap units on the side chain

A series of novel polyfluorene copolymers are developed by covalently attaching narrow band gap aryl-heterocycle units of Th-BT-TPA to the side chain of polyfluorene with an alkyl phenyl spacer through Pd-catalyzed Suzuki coupling reactions. The resulting copolymers are soluble in common organic solvents. The electrochemical, optical, and photovoltaic properties of the copolymers are studied. Electrochemical and optical analysis reveal that these polymers exhibit relatively low band gaps from 1.95 to 2.00 eV and exhibit strong absorption in the 300-620 nm region. BHJ solar cells blending copolymers PF-MR15-DBT35 with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) (1:1 weight ratio) as the active layer present a high open-circuit voltage (V_oc∼1.0 V) and a power conversion efficiency of 0.7% under simulated solar light AM1.5G (80 mW/cm²). Further investigations of other polyfluorene copolymers with narrow band gap aryl-heterocycle units on the side chain are in progress.     

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.     

Conjugated polymer consisting of dibenzosilole and quinoxaline as donor materials for organic photovoltaics

The new D–A type polymers poly(dibenzosilole-diphenylquinoxaline) (PSiPDTQ) and dibenzosilole-dibenzophenazine) (PSiFDTQ), both of which adopted benzosilole as a donor, were polymerized through a Suzuki coupling reaction. PSiPDTQ and PSiFDTQ were able to be dissolved in organic solvents and exhibited high thermal stability. Due to the appropriate LUMO energy levels, an effective charge transport was observed in PSiPDTQ and PSiFDTQ. According to X-ray diffraction measurements, a single broad diffraction peak was detected at approximately 20.5°. The π–π stacking distances (d_π) for PSiPDTQ and PSiFDTQ were 4.4 and 4.3 Å, respectively. When PSiPDTQ and PC₇₁BM were blended in a 1:3 ratio and used as the active layer in a solar cell, the resulting V_oc, J_sc, FF and PCE were 0.89 V, 5.1 mA/cm², 30.2% and 1.4%, respectively. For solar cells using a 1:6 ratio of PSiFDTQ to PC₇₁BM, the resulting V_oc, J_sc, FF and PCE were 0.98 V, 3 mA/cm², 52.8% and 1.6%, respectively. In addition, for a PSiPDTQ and PC₇₁BM blended film (1:3 ratio) with an additional layer of PFN, the PCE of the resulting solar cells was improved (relative to solar cells without PFN) to 2.1% due to the interfacial adhesion of PFN.     

The preparation and properties of bulk-heterojunction organic solar cells with indole-containing fulleropyrrolidine derivatives as acceptors

Two indole-containing fullerene derivatives, N-hydrogen-2-[3-(N-2-ethylhexylindolyl)][60]fulleropyrrolidine (EHIHC60P), and N-(2-ethylhexylindolyl))-2-[3-(N-2-ethylhexylindolyl)][60]fulleropyrrolidine (DEHIC60P) were synthesized by the typical Prato reaction. The absorption spectra, electrochemical properties of the two compounds were measured. Inverted solar cells were fabricated with the structure of ITO/ZnO/poly(3-hexylthiophene) (P3HT):fullerene derivatives/MoO₃/Ag. The highest power conversion efficiencies (PCEs) of 3.32% and 3.23% were obtained for P3HT/EHIHC60P and P3HT/DEHIC60P based solar cells at the composite ratio of 1:1 after the active layers were annealed at 150 °C under inert atmosphere, with a open-circuit voltage (V_oc) of 0.66 V and 0.74 V, respectively. For comparison, the device based on P3HT/PCBM at the same conditions showed the PCE of 3.28%, with a V_oc of 0.61 V. The influence on the photovoltaic property of the fullerene derivatives, which was induced by some subtle changes in the chemical structure was compared and discussed.     

Novel D-π-A type II organic sensitizers for dye sensitized solar cells

Four organic donor-π-conjugated-acceptor (D-π-A) type II dyes with different thiophene linkers are reported for dye sensitized solar cells (DSSCs). For the first time, a donor (triphenylamine) was introduced in type II sensitizers, and 2-hydroxybenzonitrile as acceptor/anchoring moiety was covalently linked TiO₂ particles. The dye LS203 in this series gives the best solar energy conversion efficiency of 3.4%, with J_sc = 7.4 mA cm⁻², V_oc = 0.67 V, FF = 0.69, the maximum IPCE value reaches 66.9%.