Solid-state dye-sensitized photocell based on pentacene as a hole collector

A solid-state dye-sensitized photovoltaic cell consisting of vacuum deposited pentacene onto ruthenium dye-coated TiO₂ electrode doped with iodine was fabricated. Cell delivers a short-circuit current of 3.6 mA cm⁻² and an open-circuit voltage of 415 mV at 100 mW cm^–2 (1.5 air mass). The efficiency and the fill factors of the above cell are 0.8% and 0.5%, respectively. Studies of the photocurrent action spectra showed that the dye is mainly responsible for this photocurrent generation. Preliminary results under extended illumination suggested that “long term” stability of the cell is promising.     

Dye-sensitized solar cell with the hole collector p-CuSCN deposited from a solution in n-propyl sulphide

A method is devised for the deposition of CuSCN on ruthenium bipyridyl dye coated nanocrystalline TiO₂ films from a solution in n-propyl sulphide. The dye-sensitized solid state photovoltaic cell formed was found to yield higher short-circuit photocurrent, open-circuit voltage and efficiency compared to the cells made with CuSCN by other deposition techniques. Factors affecting the stability of the cell are investigated.     

Fabrication of n–p junction electrodes made of n-type SnO2 and p-type NiO for control of charge recombination in dye sensitized solar cells

The n–p junction electrode fabricated coating nanocrystalline SnO₂ thin film with a thin layer of p-type NiO was found to increase the sensitized photocurrent and photovoltage. In addition, increase in the fill factor was noticed due to inhibition of electron back transfer from SnO₂ to the redox electrolyte (I₃⁻) by both junction effect and presence of NiO barrier, resulting in much better energy conversion efficiencies. The highest cell efficiency was obtained for the cell fabricated by immersing SnO₂ thin films in soluble Ni salts, and converting them to NiO by firing. The optimum NiO coating thickness was found to be only a few angstroms and the energy levels of the excited dye and the conduction band position of NiO suggest that the electron transfer from the excited dye to the underlying SnO₂ layer occurs by tunneling through the p-type NiO layer.     

Novel iminocoumarin dyes as photosensitizers for dye-sensitized solar cell

Novel iminocoumarin dyes (2a-c and 3a-c) having carboxyl and hydroxyl anchoring groups onto the dyes skeletons have been designed and synthesized for the application of dye-sensitized nanocrystalline TiO₂ solar cells (DSSCs). The photophysical and electrochemical studies showed that these iminocoumarin dyes are suitable as light harvesting sensitizers in DSSC application. The dyes having carboxyl and hydroxyl anchoring groups (2a-c) showed better efficiency when compared to the dyes having carboxyl group (3a-c) alone. The cell consisted of dye 2a generated the highest solar-to-electricity conversion efficiency (η) of 0.767% (open circuit voltage (V_oc) = 0.491 V, short circuit photocurrent density (J_sc) = 2.461 mA cm⁻², fill factor (ff) = 0.635) under simulated AM 1.5 irradiation (1000 W m⁻²) with a total semiconductor area of 0.25 cm². The corresponding incident photon-to-current conversion efficiency (IPCE) of the above cell was 21.38%. The overall low efficiency of the dyes is ascribed to the lack of light harvesting ability at longer wavelength region.     

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.     

A study on the electron transport properties of TiO2 electrodes in dye-sensitized solar cells

The influences of annealing temperature and different poly (ethylene glycol) (PEG) contents in nano-crystalline TiO₂ electrodes with and without N3 dye on the electron transfer in a dye-sensitized solar cell (DSSC) were investigated. It is found that the power conversion efficiency increases with the increase in annealing temperature and becomes saturated at 400–500 °C, and further increase lowers the performance which is consistent with the enhancement of the crystalline TiO₂ particles observed in X-ray diffraction (XRD) patterns and scanning electron microscopy (SEM) images. Electrochemical impedance spectroscopy (EIS) also confirms this behavior. These results have been further verified by studying the electron lifetimes (τ_e) and electron diffusion coefficients (D_e) of a bare TiO₂ and a dye-sensitized TiO₂ film using a pulsed laser spectrometer. It is noted that both the electron lifetime and the electron diffusion coefficient increase with the increase in annealing temperature. However, the evolution of rutile TiO₂ begins beyond 600 °C and this lowers the dye absorbance and the electron diffusion coefficients of TiO₂ electrodes. A similar study was made by varying the content of the PEG in the TiO₂ films. It is found that with the increase in the PEG content, a decrease in the electron lifetimes and a little hike in the electron diffusion coefficients are noted, where the cell performance remains almost the same. In addition, the dye adsorption decreases the electron lifetime and increases the electron diffusion coefficient of the TiO₂ films regardless of the PEG content and the annealing temperature.     

Solar module using dye-sensitized solar cells with a polymer electrolyte

Dye-sensitized TiO₂ solar cells assembled with a polymer electrolyte were investigated, aiming at the construction of an 8 V solar module. The individual solar cells were assembled with 4.5 cm² active area and were characterized under outdoor conditions, exhibiting an average efficiency of 0.9% per cell (at 12:00 noon). The solar module was built by connecting 13 cells in series. The integrated average daily power was estimated to be 183 mW. The present paper discusses the performance of the individual cells and the module.     

Recombination processes in dye-sensitized solid-state solar cells with CuI as the hole collector

Construction of dye-sensitized solid-state solar cells requires identification of hole collectors and understanding of the dissipative processes that limit the energy conversion efficiency. One of the hole collectors fairly well studied and giving a reasonably high efficiency is CuI. In this note we show that stoichiometrically excess iodine molecules adsorbed at the CuI surface acts as hole trapping sites (located at0.2 eV above the conduction band edge) that mediate recombination, affecting the performance of the cell. Fluorescence measurements reveal that exposure of CuI films to iodine vapor generates surface traps and as iodine diffuses to the bulk, surface trap density is greatly reduced. Methods by which the recombination originating from this effect may be circumvented are also discussed.     

Influence of the preparation conditions of TiO2 electrodes on the performance of solid-state dye-sensitized solar cells with CuI as a hole collector

Solid-state dye-sensitized solar cells (DSSCs) were fabricated in which the thin p-CuI film acts as a hole collector. Influences of the different preparation methods, composition, aging time of the TiO₂ pastes and sensitizing time on the performance of the cells were investigated. Different preparation routes for the TiO₂ paste do not obviously affect the performance of the cells. The volume of water, acetic acid and 2-propanol contained in the TiO₂ pastes and the amount of the TiO₂ powder were determined. The efficiency of the cells remains nearly stable when the aging period of the TiO₂ pastes is within one week. The favorable dying time is above 2 h. The cells having a favorable performance deliver a mean short-circuit photocurrent of 10.8 mA cm⁻² and mean open-circuit voltage of 0.61 V at 100 mW cm⁻² (1.5 AM). The mean fill factor and the mean efficiency of these cells are 0.55% and 3.7%, respectively. The short-circuit photocurrent rapidly decays after 3 h, and at the same time, the open-circuit voltage slowly decreases when the time increases, and then remains nearly stable after 24 h.     

The 3-dimensional dye-sensitized solar cell and module based on all titanium substrates

Here we report a 3-dimensional dye-sensitized solar cell (3D-DSSCs) and module simulating the fractal structure of the pine tree for capturing sunlight. Compared to traditional flat solar cells, this type of solar cell exhibits superiority of absorbing sunlight from all directions. The fabricated 3D-DSSC and module have achieved 3.36% and 3.19% efficiencies, respectively. The results show that the shade has little effect on the performance of 3D-DSSC and module. It is expected that this 3D-DSSC and module have strong potential for practical application due to their 3D light utilization.     

Synthesis of TiO2 submicro-rings and their application in dye-sensitized solar cell

In this paper, novel TiO₂ submicro-rings were synthesized via potentiostatic anodization of titanium powder coated on transparent conducting oxide glass. The TiO₂ submicro-rings film was characterized by SEM, XPS and 3D optical profiling. Accordingly, a possible growth mechanism of submicro-rings was discussed. The TiO₂ submicro-rings based dye-sensitized solar cell (DSSC) with the film thickness of ca. 3.1 μm was assembled and a conversion efficiency of 1.36% was achieved under AM 1.5 illumination. The photoelectron transport properties of TiO₂ submicro-rings based DSSC were also discussed according to the electron impedance spectroscopy.     

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.     

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.     

Natural dyes as photosensitizers for dye-sensitized solar cell

The dye-sensitized solar cells (DSC) were assembled by using natural dyes extracted from black rice, capsicum, erythrina variegata flower, rosa xanthina, and kelp as sensitizers. The I_SC from 1.142 mA to 0.225 mA, the V_OC from 0.551 V to 0.412 V, the fill factor from 0.52 to 0.63, and P_max from 58 μW to 327 μW were obtained from the DSC sensitized with natural dye extracts. In the extracts of natural fruit, leaves and flower chosen, the black rice extract performed the best photosensitized effect, which was due to the better interaction between the carbonyl and hydroxyl groups of anthocyanin molecule on black rice extract and the surface of TiO₂ porous film. The blue-shift of absorption wavelength of the black rice extract in ethanol solution on TiO₂ film and the blue-shift phenomenon from absorption spectrum to photoaction spectrum of DSC sensitized with black rice extract are discussed in the paper. Because of the simple preparation technique, widely available and low cheap cost natural dye as an alternative sensitizer for dye-sensitized solar cell is promising.     

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.     

Shiso leaf pigments for dye-sensitized solid-state solar cell

A dye-sensitized solar cell made by coating pigments in an extract from shiso leaves on a nanocrystalline film of TiO₂ and subsequent deposition of p-CuI is found to have an energy conversion efficiency of 1.3%. Both shisonin and chlorophyll contribute to light energy harvesting as seen from the photocurrent action spectrum of the cell. This is the first successful example of synergistic sensitization by dye cocktail extracted from a single natural resource. The usefulness of studies of this nature in understanding the role of multiple pigments in photosynthesis and broadening of the spectral response of dye-sensitized devices is commented, indicating also the pedagogic value of the experiment.     

New perylene derivative dyes for dye-sensitized solar cells

We have studied the influence of the spacer alkyl chain length of perylenemonoimide (PMI) dyes on the device performance in dye-sensitized solar cells (DSSCs). We observed that the dyes with longer and brunched alkyl chains exhibit higher efficiencies in DSSCs. In line with these statements we now report the highest efficiency obtained under standard conditions for a perylene imide derivative with PMI-DA1 that performs 300 mV open circuit voltage, 9.79 mA/cm² short-circuit current and 1.61% overall conversion efficiency.     

On the photophysical and electrochemical studies of dye-sensitized solar cells with the new dye CYC-B1

In this study, the photoelectrochemical characteristics of a ruthenium photosensitizer with an alkyl bithiophene group, designated as CYC-B1, are studied. The effect of mesoporous TiO₂ film thickness on the photovoltaic performance of CYC-B1 and N3 dye-sensitized solar cells was investigated. The performance of the dye-sensitized nanocrystalline TiO₂ solar cells (DSSC) fabricated using CYC-B1 dye-anchored TiO₂ photoelectrode showed a convincing enhancement in cell efficiency when the TiO₂ film thickness was increased from 3 μm (eff.=5.41%) to 6 μm (eff.=7.19%). The efficiency of the CYC-B1-sensitized DSSC was maximum at 6 μm of the TiO₂ film thickness, reached its limiting value and remained constant up to 53 μm, although a similar trend was also observed for N3 dye-sensitized DSSC, however, the maximum efficiency achieved was only at 27 μm thickness (eff.=6.75%). As expected, the photocurrent density generated in the DSSC modified by CYC-B1 dye is larger than that from N3 dye. The effect of guanidinium thiocyanate (GuSCN) (additive) addition to the electrolyte on the photovoltaic performance of DSSCs based on CYC-B1 was also investigated. Furthermore, the electrochemical impedance spectroscopy (EIS) technique and photo-transient laser method have been employed to analyze the charge transfer resistances (R_ct) and the lifetime of the injected electrons on the TiO₂ containing different thicknesses.     

Visible light induced dye-sensitized photocatalytic hydrogen production over platinized TiO2 derived from decomposition of platinum complex precursor

Pt/TiO₂ derived from complete decomposition of the surface-anchored Pt(dcbpy)Cl₂ (dcbpy = 4,4′-dicarboxy-2,2′-bipyridine) precursor (denoted as C-Pt/TiO₂) was prepared to serve as photocatalyst in visible light region. For dye-sensitized hydrogen production experiments, the photocatalyst was sensitized by Ru(2,2′-bipyridine-4,4′-dicarboxylic)₂(NCS)₂ (the N3 dye) and Ru(2,2′bipyridyl-4,4′-dicarboxylic) (4,4′- dinonyl-2,2′bipyridine) (NCS)₂ (the Z907 dye) to induce hydrogen evolution in the presence of sacrificial electron donor, triethanolamine (TEA). The hydrogen generation results showed that C-Pt/TiO₂ was found to be a much more active photocatalyst when compared to P-Pt/TiO₂, prepared by conventional method of photochemical deposition of H₂PtCl₆ (denoted as P-Pt/TiO₂). For further investigation, the photodegradation experiments in visible region were also confirmed the better photocatalytic activity of C-Pt/TiO₂. The enhanced catalytic activity is due to efficient interparticle electron transfer with the small-size and high-disperse platinum particles generated from photodeposition of Pt(dcbpy)Cl₂, which was verified by the transmission electron microscopy (TEM) measurement.     

The effects of hydrothermal temperature and thickness of TiO2 film on the performance of a dye-sensitized solar cell

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 240 °C, and the film thickness larger than 10 μm 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.