Influence of aminothiazole additives in I/I3 redox electrolyte solution on Ru(II)-dye-sensitized nanocrystalline TiO2 solar cell performance

The influence of aminothiazole additives in acetonitrile solution of an I⁻/I₃⁻ redox electrolyte on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′- bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO₂ solar cell was studied. The current–voltage characteristics were investigated under AM 1.5 (100 mW/cm²) for nine different aminothiazole compounds. The aminothiazole additives tested had varying influences on the solar cell performance. Most of the additives enhanced the open-circuit photovoltage (V_oc), but reduced the short circuit photocurrent density (J_sc) of the solar cell. Both the physical and chemical properties of the aminothiazoles were computationally calculated in order to determine the reasons that the additive influenced solar cell performance. The larger the calculated partial charge of the nitrogen atom in the thiazole, the higher the V_oc value. The V_oc value increased as the dipole moment of aminothiazoles in acetonitrile increased. Moreover, the V_oc of the solar cell also increased as the size of the aminothiazole molecules decreased. These results suggest that the electron donicity of the aminothiazole additives influenced the interaction with the TiO₂ photoelectrode, which altered the dye-sensitized solar cell performance.     

Influence of pyrazole derivatives in I/I3 redox electrolyte solution on Ru(II)-dye-sensitized TiO2 solar cell performance

The influence of pyrazole additives in an I⁻/I₃⁻ redox electrolyte solution on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized TiO₂ solar cell was studied. The current–voltage characteristics of the cell were measured using 18 different pyrazole derivatives. All of the pyrazole additives enhanced the open-circuit photovoltage (V_oc) and the solar energy conversion efficiency (η), but reduced the short-circuit photocurrent density (J_sc). Most of the pyrazoles improved fill factor (ff). The physical and chemical properties of the pyrazoles were computationally calculated in order to elucidate the reasons for the additive effects on cell performance. The greater the partial charge of the nitrogen atom at position 2 in the pyrazole group, the larger the V_oc, but the smaller the J_sc values. As the dipole moment of the pyrazole derivatives increased, the V_oc value increased, but the J_sc value decreased. The V_oc of the cell also increased as the ionization energy of the pyrazoles decreased. These results suggest that the electron donicity of the pyrazole additives affected the interaction with the nanocrystalline TiO₂ photoelectrode, the I⁻/I₃⁻ electrolyte, and the acetonitrile solvent, which changed the Ru(II)-dye-sensitized solar cell performance.     

Influence of alkylpyridine additives in electrolyte solution on the performance of dye-sensitized solar cell

The influence of alkylpyridines additive to an I⁻/I₃⁻ redox electrolyte in acetonitrile on the performance of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) dye-sensitized TiO₂ solar cell was studied. I–V measurements were performed using more than 30 different alkylpyridines. The alkylpyridine additives showed a significant influence on the performance of the cell. All the additives decreased the short-circuit photocurrent (J_sc), but most of the alkylpyridines increased the open-circuit photovoltage (V_oc) and fill factor (ff) of the solar cell. The results of the molecular orbital calculations suggest that the dipole moment of the alkylpyridine molecules correlate with the J_sc of the cell. These results also suggest that both the size and ionization energy of pyridines correlate with the V_oc of the cell. Under AM 1.5 (100 mW/cm²), the highest solar energy conversion efficiency (η) of 7.6% was achieved by using 2-propylpyridine as an additive, which was more effective than the previously reported additive, 4-t-butylpyridine.     

Effect of a redox electrolyte in mixed solvents on the photovoltaic performance of a dye-sensitized solar cell

The effect of the iodide/triiodide redox electrolyte in various organic solvents on the photoelectrochemical properties of bis(tetrabutylammonium) cis-bis(thiocyanato)bis(4-carboxy-2,2′-bipyridine-4′-carboxylato)ruthenium(II)-sensitized nanocrystalline TiO₂ solar cells was studied. Solvents with large donor numbers dramatically enhanced the open-circuit voltage (V_oc), but usually reduced the short-circuit photocurrent density (J_sc). For a mixed solvent of tetrahydrofuran (THF) and acetonitrile, V_oc increased and the fill factor decreased with increasing THF concentration, but J_sc remained relatively constant. As the partial charge of the N or O atom of the solvent molecule increased, V_oc increased, but J_sc was unchanged up to a certain value of the partial charge (for THF, −0.46). For cells using 0.3 M 4-tert-butylpyridine and 20 vol% THF in the electrolyte, a short-circuit photocurrent density of 18.23 mA cm⁻², an open-circuit voltage of 0.73 V, a fill factor of 0.73, and an overall conversion efficiency of 9.74% were obtained.     

Density functional study of alkylpyridine–iodine interaction and its implications in the open-circuit photovoltage of dye-sensitized solar cell

A density functional theory (DFT) method was used to study the monomer and intermolecular charge-transfer complexes of 22 different alkylpyridines with diiodine. DFT calculations revealed that the σ* orbital of iodine interacts with the nitrogen lone pair in pyridines. The open-circuit photovoltage (V_oc) values of a bis(tetrabutylammonium)cis-bis(thiocyanato)bis(2,2′-bipyridine-4-carboxylic acid, 4′-carboxylate)ruthenium(II) (N719) dye-sensitized nanocrystalline TiO₂ solar cell with an I⁻/I₃⁻ redox electrolyte in acetonitrile using alkylpyridines additive were compared to computational calculations on the interaction between pyridines and I₂ by a DFT method. The optimized geometries, frequency analyses, Mulliken population analyses, and interaction energies suggest that the V_oc value of the solar cell is higher, the more alkylpyridine complexes with I₂.     

Influence of alkyl dihalide gelators on solidification of dye-sensitized solar cells

Quasi-dye-sensitized solar cells were prepared by using ionic liquid-type electrolytes and gelators consisting of polyvinylpyridine and alkyl dihalides. Gelation occurred by the reaction of polyvinylpyridine and alkyl dihalides. When the chain length of the dihalides was varied, the short-circuit current (J_sc) increased with an increase in the chain length. However, the open-circuit voltage (V_oc) and fill factor (ff) slightly decreased. The increase in J_sc was brought about by the decrease in the interfacial resistances between the gel electrolyte and the counter electrode. In addition, the increase in the J_sc was explained by increases in the apparent diffusion coefficient of I⁻/I₃⁻ when the chain length increased. Decreases in V_oc and ff were explained by back-electron transfers from TiO₂ to iodine in the electrolytes. V_oc of the cells solidified by alkyldiiodide was lower than that solidified by alkyldichloride or alkyldibromide. It was explained by negatively shifted redox potential of I⁻/I₃⁻, compared with those for Cl⁻/Cl₂ or Br⁻/Br₂.     

Influence of electrolytes on the photovoltaic performance of organic dye-sensitized nanocrystalline TiO2 solar cells

We have studied the influence of electrolytes on the photovoltaic performance of mercurochrome-sensitized nanocrystalline TiO₂ solar cells using LiI, LiBr, and tetraalkylammonium iodides as the electrolyte. Short-circuit photocurrent density (J_sc) and open-circuit photovoltage (V_oc) depended strongly on the electrolyte. J_sc of 3.42 mA cm⁻² and V_oc of 0.52 V were obtained for the LiI electrolyte and J_sc of 2.10 mA cm⁻² and V_oc of 0.86 V were obtained for the Pr₄NI electrolyte. This difference in photovoltaic performance was due to the change in the conduction band level of the TiO₂ electrode. Large V_oc of 0.99 V was obtained for the LiBr electrolyte due to the large energy gap between the conduction band level of TiO₂ and the Br/Br₂ redox potential. Solar cell performance also depended strongly on organic solvent, suggesting that the physical properties of solvents such as Li ion conductivity and donor number affect photovoltaic performance.     

Highly efficient photon-to-electron conversion with mercurochrome-sensitized nanoporous oxide semiconductor solar cells

Dye-sensitized solar cells based on nanoporous oxide semiconductor thin films such as TiO₂, Nb₂O₅, ZnO, SnO₂, and In₂O₃ with mercurochrome as the sensitizer were investigated. Photovoltaic performance of the solar cell depended remarkably on the semiconductor materials. Mercurochrome can convert visible light in the range of 400–600 nm to electrons. A high incident photon-to-current efficiency (IPCE), 69%, was obtained at 510 nm for a mercurochrome-sensitized ZnO solar cell with an I⁻/I₃⁻ redox electrolyte. The solar energy conversion efficiency under AM1.5 (99 mW cm⁻²) reached 2.5% with a short-circuit photocurrent density (J_sc) of 7.44 mA cm⁻², a open-circuit photovoltage (V_oc) of 0.52 V, and a fill factor (ff) of 0.64. The J_sc for the cell increased with increasing thickness of semiconductor thin films due to increasing amount of dye, while the V_oc decreased due to increasing of loss of injected electrons due to recombination and the rate constant for reverse reaction. Dependence of photovoltaic performance of mercurochrome-sensitized solar cells on semiconductor particles, light intensity, and irradiation time were also investigated. High performance of mercurochrome-sensitized ZnO solar cells indicate that the combination of dye and semiconductor is very important for highly efficient dye-sensitized solar cells and mercurochrome is one of the best sensitizers for nanoporous ZnO photoelectrode. In addition, a possibility of organic dye-sensitized oxide semiconductor solar cells has been proposed as well as one using metal complexes.     

Photosensitization of nanocrystalline TiO2 films by a polymer with two carboxylic groups, poly (3-thiophenemalonic acid)

Photovoltaic devices were assembled using a conducting polymer; poly (3-thiophenemalonic acid) sensitized TiO₂ electrodes and an electrolyte containing I₃⁻/I⁻ redox couple. This cell exhibited a short-circuit photocurrent (J_sc) of 6.65 mA cm⁻², an open circuit voltage (V_oc) of 355 mV and an efficiency of 1.5% under the illumination of 100 mW cm⁻² (AM 1.5). Addition of an ionic liquid, 1-methyl 3-n-hexylimidazolium iodide, into the electrolyte led to an improvement in the cell performances, achieving an overall efficiency of 1.8% under the same illumination. The average cell characteristics of the later devices are , with a fill factor of 0.65.     

Temperature dependence and the oscillatory behavior of the opto-electronic properties of a dye-sensitized nanocrystalline TiO2 solar cell

A dye-sensitized TiO₂ solar cell was developed and characterized. The I–V (current–voltage) characteristics were studied at different temperatures from −40°C to 80°C. The opto-electronic properties of the cell depend on factors like ambient temperature and the time constants of the redox processes at the cell interfaces. The temperature dependence of V_oc and I_sc were clearly demonstrated. I_sc increased with increasing temperature above room temperature, where as V_oc increased with decreasing temperature below room temperature. The opto-electronic properties showed oscillatory behavior especially at low temperatures, which may be attributed to the different velocities of the redox processes occurring at the TiO₂/dye, dye/electrolyte and the electrolyte/counter electrode interfaces.     

On the use of triethylamine hydroiodide as a supporting electrolyte in dye-sensitized solar cells

For the first time, the application of a molten salt, triethylamine hydroiodide (THI), as a supporting electrolyte was investigated for the dye-sensitized solar cells (DSSCs). Titanium dioxide (TiO₂) electrode was modified by incorporation of high- and low-molecular weight poly(ethylene glycol) along with TiO₂ nanoparticles of two different sizes (300 nm (30 wt%) and 20 nm (70 wt%)). The highest apparent diffusion coefficient (D) of 8.12×10⁻⁶ cm² s⁻¹ was obtained for I⁻ (0.5 M of THI) from linear sweep voltammetry (LSV). Short-circuit current density (J_sc) increases with the concentration of THI whereas open-circuit potential (V_oc) remains the same. Optimum J_sc (19.28 mA cm⁻²) and V_oc (0.7 V) with a highest conversion efficiency (η) of 8.45% were obtained for the DSSC containing 0.5 M of THI/0.05 M I₂/0.5 M TBP in CH₃CN. It is also observed that the J_sc and η of the DSSC mainly relates with the D values of I⁻ and charge-transfer resistances such as R_ct1 and R_ct2 operating along Pt/TiO₂ electrolyte interface, obtained from LSV and electrochemical impedance spectroscopy (EIS). For comparison, tetraethylammonium iodide (TEAI) and LiI were also selected as supporting electrolytes. Though both the THI and TEAI have similar structures, replacement of one methyl group by hydrogen improves the efficiency of the DSSC containing the former electrolyte. Further, the DSSC containing THI exhibits higher J_sc and η than LiI (7.70%), from which it is concluded that THI may be used as an efficient and alternative candidate to replace LiI in the current research of DSSCs.     

Effects of pH of a hybrid gel incorporated with 3-aminopropyltrimethoxysilane on the performance of a quasi-solid state dye-sensitized solar cell

Network hybrid gel prepared with tetraethyl orthosilicate, 3-aminopropyltrimethoxysilane (APS) and poly(ethylene glycol) was used as an electrolyte matrix in a quasi-solid state dye-sensitized solar cell (DSSC). Change in pH of this hybrid gel by varying the composition of APS was found to have remarkable effects on the photoelectrochemical performance of the cell. The hybrid gel matrix, having silane polymer backbones with free amine functionality, was characterized by FT-IR spectra and FE-SEM images, and the assembled DSSC by photocurrent-voltage and incident photon to current conversion efficiency curves. The unsealed, quasi-solid state DSSC with the hybrid gel has shown an increase in the open-circuit voltage (V_oc) and a steady decrease in the short-circuit photocurrent (J_sc), with increase in the content of APS. A maximum conversion efficiency of 4.5% was obtained for a DSSC by using 20% of APS in its hybrid gel at a light intensity of 100 mW cm⁻². Upon replacing the amino group of APS by bulkier aniline and benzophenoaniline groups, conversion efficiencies of the corresponding DSSCs were reduced. Variations in the V_oc and J_sc are explained in terms of shift of the flat band potential of TiO₂ and a complex formation between I₃⁻ and −NH₂ of APS of the electrolyte.     

Manufacturing method for transparent electric windows using dye-sensitized TiO2 solar cells

The transparent electric windows based on dye-sensitized nanocrystalline TiO₂ solar cells have been prepared. The solar cell consists of dye-sensitized TiO₂ electrode with a TiO₂ layer of an about 8 μm thickness and of a 80×80 mm² active area, Pt counter electrode and redox electrolyte. The solar cell shows a transmittance of approximately 60% in the visible range and an open-circuit voltage (V_oc) of 0.64 V and a short-circuit photocurrent (J_sc) of 250 mA. A moderately transparent electric window composed of nine unit solar cells in series generates V_oc of 5.7 V and J_sc of 220 mA at one sun light intensity.     

Characterization of CuInSe2/CdS thin-film solar cells prepared using CBD

CuInSe₂/CdS thin-film heterojunction solar cells were fabricated entirely by chemical bath deposition technique. The illuminated J−V characteristics of the devices prepared with different thicknesses of CdS and CuInSe₂ were studied. The typical solar cell parameters obtained for the best cell are: V_oc = 365 mV, J_sc = 12 mA/cm², FF = 61%, and η = 3.1% under an illumination of 85 mW/cm² on a cell of active area 0.1 cm². The J−V and C−V characteristics under dark condition and the spectral response were also studied for the best cell. The diode quality factor obtained is 1.7.     

High-efficiency CIGS solar cells with modified CIGS surface

CIGS films were treated in In–S aqueous solution for high-efficiency CIGS solar cells. The In–S aqueous solution contained InCl₃ and CH₃CSNH₂ (thioacetamide). The In–S treatment modified the CIGS surface favorably for high-efficiency CIGS solar cells as evidenced by the increase in V_oc, J_sc and FF. The In–S treatment formed thin CuInS₂ layer on the CIGS surface which contributes to the high efficiency and stable performance of the CIGS solar cell. The best cell showed an efficiency of 17.6% (V_oc=0.649 V, J_sc=36.1 mA/cm² and FF=75.1%) without any annealing and light soaking before I–V measurement.     

Influence of 1-methyl-3-propylimidazolium iodide on I3/I redox behavior and photovoltaic performance of dye-sensitized solar cells

In this paper, we investigated redox behavior of I⁻ and I₃⁻ in 3-methoxypropionitrile (MePN) with different concentrations of 1-methyl-3-propylimidazolium iodide (MPII) and iodine by cyclic voltammetry and electrochemical impedance spectroscopy. It was found that the apparent diffusion coefficient (D) values of triiodide and iodide ions, the serial resistance (R_s) and the charge-transfer resistance (R_ct) decreased slightly with increase of the concentration of I₃⁻ in MePN containing 1.4 M MPII. Moreover, the R_ct and D values of triiodide and iodide ions affection on dye-sensitized solar cells (DSCs) should be considered as a whole. The DSCs with the electrolyte (1.4 M MPII, 0.1 M LiI, 0.1 M I₂, 0.5 M TBP, in MePN) gave short circuit photocurrent density (J_sc) of 14.44 mA/cm², open circuit voltage (V_oc) of 0.72 V, and fill factor (FF) of 0.69, corresponding to the photoelectric conversion efficiency (η) of 7.17% under one Sun (AM1.5).     

The effect of temperature on the charge transport and transient absorption properties of K27 sensitized DSSC

The charge transport and transient absorption properties of K27 dye-sensitized solar cell have been investigated. The current–voltage (I–V) characteristics of the solar cell were analyzed by the thermionic emission theory. The ideality factor, barrier height and series resistance values of the solar cell were determined. The ideality factor higher than unity indicated the presence of non-ideal behavior in current–voltage characteristics at lower voltages. At the higher voltages, the charge transport mechanism for the solar cell is controlled by a space-charge limited current (SCLC) with an exponential distribution of traps. The built potential values are determined from capacitance–voltage plot and were found to be 0.14 and 0.58 V, respectively. The transient absorption data of K27 DSSC device suggest that the fast and slow phases are taking place. While the fast phase corresponds to regeneration of the dye cation by the iodide redox couple, the slow phase corresponds to the decay of long-lived I₂⁻/ TiO₂ electron absorption. The best conversion efficiency for K27 DSSC was found to be 0.317% under 100 mW/cm² (FF=0.584, V_oc=480 mV, I_sc=1.131 mA). The photocurrent results indicate that the photogeneration of charge carriers is a monophotonic process.     

Photovoltaic effect in single-layer organic solar cell devices fabricated with two new imidazolin-5-one molecules

Organic solar cells were fabricated with two new imidazolin-5-one molecules as active layers. The use of imidazolin-5-ones, derivatives of a biomolecule chromophore, for photovoltaic applications is particularly attractive due to its biodegradable nature and tunable properties. Single-layer devices with two analogues of imidazolin-5-ones were prepared and characterized. Devices fabricated with one of the molecules as the active layer showed a maximum J_sc of 0.52 μA cm⁻² and V_oc of 0.68 V at an incident power of 20.32 mW cm⁻², while the other set of devices showed a maximum J_sc of 0.63 μA cm⁻² and V_oc of 0.57 V at the same incident power.     

5–20 MeV proton irradiation effects on GaAs/Ge solar cells for space use

This paper reports the high-energy proton irradiation effects on GaAs/Ge space solar cells. The solar cells were irradiated by protons with energy of 5–20 MeV at a fluence ranging from 1×10⁹ to 7×10¹³ cm⁻², and then their electric parameters were measured at AM0. It was shown that the I_sc, V_oc and P_max degrade as the fluence increases, respectively, but the degradation rates of I_sc, V_oc and P_max decrease as the proton energy increases, and the degradation is relative to proton irradiation-induced defect Ec−0.41 eV in irradiated GaAs/Ge cells.     

Enhancement in the performance of dye-sensitized solar cells containing ZnO-covered TiO2 electrodes prepared by thermal chemical vapor deposition

A ZnO-covered TiO₂ (denoted as ZnO/TiO₂) film was prepared by incorporating a small quantity of particulate ZnO in a TiO₂ matrix by thermal chemical vapor deposition. When used in a dye-sensitized solar cell, an enhancement was observed in both short-circuit photocurrent (J_sc) and open-circuit voltage (V_oc) by 12% and 17%, respectively, relative to those of a cell containing a bare TiO₂ film. The observed J_sc enhancement is attributed to the increase in the surface area of the ZnO/TiO₂ film, and the V_oc enhancement to the formation of a potential barrier by ZnO at TiO₂/electrolyte interface. The films were characterized by FE-SEM, EDX, and XRD.