Sten-Eric Lindquist

A 5% efficient photoelectrochemical solar cell based on nanostructured ZnO electrodes

Nanoporous ZnO electrodes, dye-sensitized with a ruthenium bipyridyl complex, were used as photoanodes in photoelectrochemical solar cells. By improving the interfacial contact between dyes and ZnO particles in the film, overall solar-to-electric energy conversion efficiencies of up to 5% were obtained. The solar cell performance was studied as a function of film thickness, residence time of the electrodes in the dye solution, electrolyte composition and light intensity.

Photoelectrochemical studies of oriented nanorod thin films of hematite

Thin films consisting of nanorods of hematite (α-Fe2O3) with controlled orientation onto transparent conductive glass substrates have been tested as photoelectrochem. cells. These films allow a more efficient transport and collection of photogenerated electrons through a designed path compared to films constituted of sintered spherical particles. Expts. have been carried out taking into account the effect of morphol., orientation, film thickness, electrolyte compn., and dye sensitization. The results from a three-electrode system, with 0.1 M KI in water (pH 6.8) as electrolyte, illuminated either through the electrolyte/electrode interface or through the substrate (F:SnO2)/electrode interface, show an improvement of the IPCE (incident photon-to-current conversion efficiency) of 100 and 7 times, resp., compared to work done earlier on thin films with spherical particles. Increasing the pH in the electrolyte from 6.8 to 12.0 also increases the IPCE by a factor two. For a sandwich-type cell, with 0.5 M LiI and 0.5 mM I2 in ethylene carbonate/propylene carbonate (50:50% by wt.) electrolyte, the IPCE reaches 56% at 340 nm.

Investigation of influence of redox species on the interfacial energetics of a dye-sensitized nanoporous TiO2 solar cell

The photoelectrochem. behaviors of dye-sensitized nanoporous TiO2 solar cells are studied under influences of light intensity, redox couple concn., temp., different cations and water in the nonaq. soln. The value of the ideality factor of dyed nanoporous TiO2 film is detd. to be 1.08. The diode behavior of the dyed nanoporous TiO2 film approaches an ideal rectification characteristic. The rate of the reaction of I3- with the electron at the surface of the dyed TiO2 electrode is of first order, like the redn. of I3- at the Pt electrode. By anal. of the relationship of the photovoltage with temp., the activation energies of the back-reaction for dyed nanoporous TiO2 electrodes in different solns. are obtained. Cations of different kinds and water are found to modify the interfacial properties of the dyed TiO2 electrode. Finally, a quant. relationship between the short-circuit photocurrent and the light intensity, the I3- concn. is obtained and used to explain the diffusion-controlled photocurrent. The cor. diffusion coeff. of I3- is 5.4-6.2×10-6 cm2/s in a CH3OCH2CN soln.

Aqueous Photoelectrochemistry of Hematite Nanorod-Array

A unique nanostructured rod-like morphol. of hematite (α-Fe2O3), designed with no grain boundaries, has been investigated for the aim of a direct splitting of water at the hematite/electrolyte interface. Photoelectrochem. properties were studied by steady-state measurements on electrodes with controlled morphol. and film thickness in aq. electrolyte. The hematite electrodes were able to generate incident photon-to-current efficiencies (IPCEs) of ∼8% by illumination through the substrate with a wavelength of 350 nm and a light intensity of 0.1 mW cm-2 without any applied voltage. On the basis of light intensity studies, it is concluded that charge carrier recombinations due to the poor semiconductor properties in combination with slow oxidn. kinetics at the hematite nanorods/electrolyte interface are the dominating problems. However, the high IPCE values obtained indicates that purpose-built nanorods of hematite is one significant way to strikingly lower the recombination rate of hematite material.

Photoelectrochemical studies of colloidal TiO2 films: The effect of oxygen studied by photocurrent transients

The effect of oxygen in nanocryst. colloidal TiO2 film photoelectrodes were studied by optically induced photocurrent transient measurements. O2 played an important role in the recombination of electrons and holes. Some effects esp. assocd. with the nanoporous morphol. of these photoelectrodes are discussed.

Nanostructured ZnO electrodes for photovoltaic applications

Abstract Photoelectrochemical properties of nanostructured ZnO (wurtzite) electrodes have been investigated. Studies were carried out on various types of electrodes with controlled morphology, particle size and doping. The monochromatic photon-to-current conversion efficiencies were recorded in the UV spectral region on bare ZnO and in the visible region on ruthenium dye-sensitized cells. The results show relatively high efficiencies for such systems and demonstrate the potential of ZnO nanostructured cells as materials for photovoltaic applications.

Verification of High Efficiencies for the Grätzel Cell : A 7% Efficient Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films.

Verification of High Efficiencies for the Gratzel Cell : A 7% Efficient Solar Cell Based on Dye-Sensitized Colloidal TiO2 Films.

Photoelectrochemical studies of colloidal TiO2-films: the charge separation process studied by means of action spectra in the UV region

Charge sepn. in sintered colloidal TiO2 film electrodes was studied by action spectra in SCN-/(SCN)2- the UV region. Electrodes with different film thicknesses were studied. Current generation is most efficient close to the back contact. Monochromatic quantum efficiency of ≤77% and optimum overall quantum efficiency were attained at a colloidal film thickness of ∼4 μm. Illumination through the back side contact gives a theor. quantum efficiency of 100% to a depth of 0.5 μm from the back contact. The origin of the unexpectedly high current generation in the colloidal films was studied.

Environmental aspects of electricity generation from a nanocrystalline dye sensitized solar cell system

A Life Cycle Assessment, LCA, of a nanocrystalline dye sensitized solar cell (ncDSC) system has been performed, according to the ISO14040 standard. In brief, LCA is a tool to analyse the total environmental impact of a product or system from cradle to grave. Six different weighing methods were used to rank and select the significant environmental aspects to study further. The most significant environmental aspects according to the weighing methods are emission of sulphur dioxide and carbon dioxide. Carbon dioxide emission was selected as the environmental indicator depending on the growing attention on the global warming effect. In an environmental comparison of electricity generation from a ncDSC system and a natural gas/combined cycle power plant, the gas power plant would result in 450 g CO2/kWh and the ncDSC system in between 19–47 g CO2/kWh. The latter can be compared with 42 g CO2/kWh, according to van Brummelen et al. “Life Cycle Assessment of Roof Integrated Solar Cell Systems, (Report: Department of Science, Technology and Society, Utrecht University, The Netherlands, 1994)” for another thin film solar cell system made of amorphous silicon. The most significant activity/component contributing to environmental impact over the life cycle of the ncDSC system is the process energy for producing the solar cell module. Secondly comes the components; glass substrate, frame and junction box. The main improvement from an environmental point of view of the current technology would be an increase in the conversion efficiency from solar radiation to electricity generation and still use low energy demanding production technologies. Also the amount of material in the solar cell system should be minimised and designed to maximise recycling.

A new method for manufacturing nanostructured electrodes on glass substrates

The present paper describes a new method for manufacturing a nanostructured porous layer of a semiconductor material on a conducting plastic substrate for use in an electrochemical or photoelectrochemical cell. The method involves the deposition of a layer of semiconductor particles on conducting plastic and the compression of the particle layer to form a mechanically stable, electrically conducting, porous nanostructured film at room temperature. Photoelectrochemical characteristics of the resulting nanostructured films are presented showing, for example, overall solar to electric conversion efficiencies of up to 4.9% (0.1 sun). The potential use of the new manufacturing method in future applications of nanostructured electrodes is discussed.