Flexible and light weight copper indium diselenide solar cells on polyimide substrates

Thin film flexible CuInSe₂ (CIS) solar cells have been fabricated for the first time on light-weight polymeric substrates. Evaporated Cu---In alloy precursors were selenized in H₂Se atmosphere at around 400°C to grow the CIS absorber layers. Low temperature techniques which are compatible with the polymeric substrates were used to deposit the window layers of CdS and ZnO. The demonstrated active area conversion efficiency of 9.3% makes this light-weight device very attractive for many terrestrial and space power generation applications where high specific power and mechanical flexibility are needed.     

Effects of spectral variation on the device performance of copper indium diselenide and multi-crystalline silicon photovoltaic modules

We present results of an experimental investigation of the effects of the daily spectral variation on the device performance of copper indium diselenide and multi-crystalline silicon photovoltaic modules. Such investigations are of importance in characterization of photovoltaic devices. The investigation centres on the analysis of outdoor solar spectral measurements carried out at 10 min intervals on clear-sky days. We have shown that the shift in the solar spectrum towards infrared has a negative impact on the device performance of both modules. The spectral bands in the visible region contribute more to the short circuit current than the bands in the infrared region while the ultraviolet region contributes least. The quantitative effects of the spectral variation on the performance of the two photovoltaic modules are reflected on their respective device performance parameters. The decrease in the visible and the increase in infrared of the late afternoon spectra in each case account for the decreased current collection and hence power and efficiency of both modules.     

Effects of recombination parameters in pn indium phosphide solar cells

This work, using a numerical code PC-1D, describes the effects of surface and bulk recombination on the performance of p⁺n indium phosphide solar cells. It is shown that surface recombination velocity and minority carrier diffusion lengths play a dominant role in controlling the efficiency of p⁺n cells. In order to have an acceptable series resistance, a p⁺n cell must have an emitter that is thicker than a n⁺p cell emitter. Consequently the performance of a p⁺n cell is more sensitive to the front surface recombination velocity. Improved surface and bulk recombination parameters can lead to cell efficiencies in excess of 24% AMO at 25°C.     

Efficiency and degradation of a copper indium diselenide photovoltaic module and yearly output at a sunny site in Jordan

The present work mainly deals with the testing and modeling of a commercially-available copper indium diselenide (CIS) ST40 module from the former Siemens Solar Industries (SSI). For this purpose, a large quantity of current/voltage characteristics were measured in the Paul Scherrer Institute (PSI)’s photovoltaic test-facility under different cell temperatures, solar irradiation and air mass, AM, conditions. They were used to develop a semi-empirical efficiency model to correlate all measured data sets. The goal was to make available a model, allowing quick and accurate calculation of the performance of the CIS module under all relevant operating conditions.

For the undegraded state of the module, the efficiency model allowed us to deduce the efficiency at Standard Test Conditions, STC, and its temperature coefficient at STC, which were 11.58% and minus 0.050%/°C, respectively. The output of the undegraded module under STC was found to be 42.4 W, i.e., 6% higher than specified by the manufacturer (40 W). Furthermore, the efficiency does not decrease with increasing air mass. At a cell temperature of 25 °C and a relative air mass of 1.5, the module has a maximum in efficiency of 12.0% at an irradiance of about 650 W/m². This indicates that the series-resistance losses become significant at higher irradiances. Hence, improving the transparent conducting oxide (TCO) electrode on the front side of the cells might lead to a higher output at high irradiances.

Identical testing and modeling were repeated after having exposed the module to real weather conditions for one year. We found that the STC efficiency was reduced by 9.0%, from 11.58 down to 10.54%. The temperature coefficient of the efficiency had changed from minus 0.050 %/°C to minus 0.039%/°C. These results indicate possible chemical changes in the semiconductor film. The output of the module at STC was reduced by 9.0% from 42.4 W down to 38.6 W.

Using meteorological data from a sunny site in the South of Jordan (Al Qauwairah) and the efficiency model presented here allows us to predict the yearly electricity yield of the CIS module in that area. Prior to degradation, the yield was found to be 362 kWh/m² for the Sun-tracked module; and 265 kWh/m² for the fix-installed module (South-oriented, at an inclination angle of 30°). After degradation the corresponding yields were found to be 334 and 241 kWh/m²; meaning losses of 8.4% and 9.5%, respectively. (Note: all units of energy, kWh, are referred to the active cell area.) Having available efficiency models for other module types, similar predictions of the yield can be made, facilitating the comparisons of the yearly yields of different module types at the same site. This in turn allows selecting the best module type for a particular site.     

Tin doping in spray pyrolysed indium sulfide thin films for solar cell applications

This paper presents studies carried out on tin-doped indium sulfide films prepared using Chemical Spray Pyrolysis (CSP) technique. Effect of both in-situ and ex-situ doping were analyzed. Ex-situ doping was done by thermal diffusion, which was realized by annealing Sn/In₂S₃ bilayer films. In-situ doping was accomplished by introducing Sn into the spray solution by using SnCl₄·5H₂O. Interestingly, it was noted that by ex-situ doping, conductivity of the sample enhanced considerably without affecting any of the physical properties such as crystallinity or band gap. Analysis also showed that higher percentage of doping resulted in samples with low crystallinity and negative photosensitivity. In-situ doping resulted in amorphous films. In contrast to ex-situ doping, ‘in- situ doping’ resulted in widening of optical band gap through oxygen incorporation; also it gave highly photosensitive films.     

Polycrystalline n-CuInSe2 photoelectrochemical solar cells — Electrochemistry and deposition of copper and indium at the photoanode and the accompanying efficiency enhancement

The electrochemical behaviour of polycrystalline n-CuInSe₂ (CIDS) with respect to removal of oxygen, anodic prepolarization, and deposition and stripping of copper and indium in aqueous KC1 solution has been examined. Oxygen contributed to cathodic currents, while anodic prepolarization caused the appearance of a Cu²⁺/Cu couple. The reduction of the copper ion (Cu²⁺) to metallic copper at CIDS was found to be quasi-reversible and diffusion-controlled. Initially, deposited copper facilitated indium deposition at the CIDS electrode. Aged CIDS as well as CIDS deposited with copper underwent stripping (oxidation) with low currents at more negative potentials which could be prevented by codeposition of copper and indium. Further, deposition of copper, or copper and indium on CIDS was observed to improve the charge transfer at the CIDS/ electrolyte interface. These results were applied for the fabrication of CIDS based photoelectrochemical solar cells employing polysulphide redox electrolyte. It was found that codeposition of copper and indium on CIDS electrode led to significant enhancement in the cell efficiency (rises to 11.5% from 3.4%) and slowed down the short-circuit current decay. A part (70–80%) of the decayed short-circuit current could be regained by renewing the CIDS electrode with codeposition treatment for the second time (redeposition). The possibility of applying deposition-redeposition treatment to regulate the output current was suggested. Previously unexplained cooperative effects of Cu⁺ and In³⁺ in polysulphide electrolyte on the cell efficiency were traced to the facilitated deposition of indium on the copper deposited CIDS electrode from the appropriate salt solutions.     

On the relevance of mass transport in thin layer nanocrystalline photoelectrochemical solar cells

A comprehensive analysis of the diffusion and migration processes in the steady state operation of mesoporous photoelectrochemical solar cells has been attempted. The dye sensitized TiO₂ nanocrystalline solar cell utilizing the iodide/triiodide redox mediator serves as the system of reference. The porous nature of the semiconductor plays an important role in this process. Efficient design characteristics for such cells are obtained in order to minimize, e.g., the concentration overpotential, thus minimizing one of the sources of loss in such cells.The models developed illustrate operational aspects such as concentration profiles in the cell under the conditions relevant to existing systems, the limiting or maximum possible currents in the nanocrystalline PEC device, and the anticipated mass-transfer overpotential as a function of current density. The geometric and structural properties of the photoanode as well as the relative position of the counter-electrode with respect to the mesoporous film photoanode can be better exploited towards an efficient operation of the solar energy conversion device.The repercussions of the variation of solar cell design parameters are illustrated experimentally by the performance of practical application devices. These serve as evidence towards the plausibility and the validity of a mass transfer model for the electrolyte function in nanocrystalline PECs.     

Performance of electron beam deposited tungsten doped indium oxide films as anodes in organic solar cells

Tungsten doped indium oxide (IWO) thin films have been investigated as an alternative to indium tin oxide (ITO) anodes in organic solar cells (OSCs). The surface morphology, electrical, and optical properties of the IWO films grown by electron beam deposition were studied as a function of oxygen flow rate. For 120 nm thick IWO films deposited on float glass substrates at 350 °C and oxygen flow rate of 35 sccm, an electrical resistivity of 4.78×10⁻⁴ Ω cm and average transmittance of over 78% between 400 and 2000 nm were obtained. OSCs based on poly(3-hexylthiophene) and [6,6]-phenyl C₆₁-butlyric acid methyl ester were prepared on glass/IWO electrodes and the device performance was investigated as a function of IWO films with different oxygen flow rates. OSCs fabricated on the optimum IWO anode (oxygen flow rate of 30-35 sccm) exhibited a power conversion efficiency of ∼3.5%, which is comparable with the same device made on commercial glass/ITO electrodes (3.75%).     

Charge transport in a-Si: H PIN solar cells under AC excitation

We have made I-V and impedance measurements on a-Si: H PIN solar cells as a function of the frequency and bias voltage to understand the mechanisms that limit the charge transport under AC excitation. The measurements covered the range of frequencies from 1 Hz to 1 MHz. It is concluded that the interaction between gap states and extended states rather than the band transport is the limiting mechanism on the charge transport.     

Effect of indium and tin contamination on the efficiency and electronic properties of organic bulk hetero-junction solar cells

Organic photovoltaic devices using an electrode of indium tin oxide (ITO) coated with a buffer layer of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) exposed to controlled humidity during fabrication showed a 65-75% decrease in efficiency and displayed S-shaped J-V curves, changes, which are attributed to different levels of indium and tin migration into the PEDOT:PSS film. A distinct shift in the secondary electron cut-off in the UV Photoelectron spectra (UPS) of ITO/PEDOT:PSS samples exposed to controlled humidity indicate an increase of the dipole at the ITO/PEDOT:PSS interface, which could explain the appearance of S-shaped J-V curves. Additionally, the electron density at low binding energies is reduced for the humidity exposed PEDOT:PSS suggesting a second mechanism for decreased device performance.     

Studies of coupled charge transport in dye-sensitized solar cells using a numerical simulation tool

In this paper, we present a simulation platform designed to study coupled charge transport in dye-sensitized solar cell (DSC) devices. The platform, SLICE, is used to study the influence of ions in the electrolyte on electron transport in the nanoporous medium. The simulations indicate that both cationic and anionic properties should be considered when modelling DSCs and similar systems. Additionally, it was found that the effective permittivity coefficient, ε, has no influence on the electron transport when the ionic concentration is sufficiently high due to the strong coupling between the respective charged species.     

Losses due to polycrystallinity in thin-film solar cells

The highest efficiency thin-film polycrystalline CuIn_1−xGa_xSe₂ (CIGS) and CdTe solar cells are compared directly with crystalline Si and GaAs cells with similar respective bandgaps. The excess efficiency losses (6.3% for CIGS and 9.9% for CdTe) are quantitatively separated into eight categories. In each case, the impact of polycrystallinity is evaluated, and the differential losses are identified as being directly attributable to polycrystallinity or due to other causes. Approximately, two-thirds of the excess loss for polycrystalline cells is clearly due to polycrystallinity. Thus, strategies such as grain passivation to reduce the impact of polycrystallinity should be examined, but at the same time conventional approaches for incremental improvement should receive attention.     

Influence of electrolyte in transport and recombination in dye-sensitized solar cells studied by impedance spectroscopy

The main features of the characteristic impedance spectra of dye-sensitized solar cells are described in a wide range of potential conditions: from open to short circuit. An equivalent circuit model has been proposed to describe the parameters of electron transport, recombination, accumulation and other interfacial effects separately. These parameters were determined in the presence of three different electrolytes, both in the dark and under illumination. Shift in the conduction band edge due to the electrolyte composition was monitored in terms of the changes in transport resistance and charge accumulation in TiO₂. The interpretation of the current–potential curve characteristics, fill factor, open-circuit photopotential and efficiency in the different conditions, was correlated with this shift and the features of the recombination resistance.     

The effect of introducing a buffer layer to polymer solar cells on cell efficiency

The effect of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) as a buffer layer was investigated in polymer solar cells (PSCs). Four different types of PEDOT:PSS were used: PH, PH500 and their DMSO (dimethylsulfoxide)-doped counterparts. The efficiency of PSCs was independent of the electric conductivity of the buffer layer as a bulk property while it was significantly related to interfacial properties between the buffer layer and a bulk-heterojunction (BHJ) layer. The interfacial properties included charge transfer resistance (R_CT), hole mobility (μ_h) and contact angle (θ) of the solution of BHJ on the buffer layer. Lower R_CT, higher μ_h and smaller θ led to the higher fill factor (up to 72%), enabling highly efficient PSCs with efficiency (η)=4.25%.     

The role of bypass diodes in the failure of solar battery charging stations in Thailand

This paper focuses on the failure of bypass diodes in solar battery charging stations (SBCS) in Thailand. The Thai government has installed over 1000 SBCS in unelectrified villages to be used to charge 12-V batteries for household lights and small appliances. The unnecessary inclusion of bypass diodes in these systems created an unexpected failure mode when villagers misconnected their batteries with reverse polarity. In a survey of 31 stations, 18 stations were disabled by burnt-out bypass diodes. The electrical engineering theory of this failure mode is analyzed. In addition, we discuss how the bypass diode failures have been compounded by lack of end-user feedback to the implementing agencies.     

A channel flow cell system specifically designed to test the efficiency of redox shuttles in dye sensitized solar cells

The construction and use of a thin layer flow cell test system employing a TiO₂ working electrode, a platinum quasi-reference electrode and the ruthenium dye (H₂-dcbpy)Ru(NCS)₂ (H₂-dcbpy=2,2′-bipyridine-4,4′-dicarboxylic acid) is described. The efficient design enables significant advantages to be gained over presently available procedures for the measurement of photocurrents of dye-sensitized solar cells. The widely used iodide/triiodide redox shuttle system has been investigated over a wide range of conditions. A linear dependence of photocurrent on cation radius was revealed. Under certain conditions, the photocurrent measured in the presence of the Li⁺ cation is five times larger than when the (C₄H₉)₄N⁺ cation is used. Additionally, the addition of low concentrations of cations with small diameters has a significant catalytic enhancement effect on the photocurrent. Other redox shuttles, based on ferrocene, thiocyanate, triiodide and bromide, were tested for their performance in the flow cell and compared to iodide. However, despite some apparent thermodynamic advantages, the photocurrents obtained with these redox shuttles were more than two orders of magnitude lower than those measured with iodide. This finding implies that the efficiency of redox shuttles is limited by kinetic restraints rather than their thermodynamic properties and confirms that the iodide/triiodide system is the dominant redox shuttle.     

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.     

Experimental study of variations of the solar spectrum of relevance to thin film solar cells

The influence of variations in the incident solar spectrum on solar cells is often neglected. This paper investigates the magnitude of this variation and its potential influence on the performance of thin film solar cells in a maritime climate. The investigation centres on the analysis of a large number of measurements carried out in Loughborough, UK, at 10 min intervals over a period of 30 months. The magnitude of the spectral variation is presented both on a daily and a seasonal basis. Of the different thin film materials studied, amorphous silicon is shown to be the most susceptible to changes in the spectral distribution, with the “useful fraction” of the light varying in the range +6% to −9% of the annual average, with the maximum occurring in summer time.     

保持太阳电池稳定可靠的焊接品质

<正>一引言持续上涨的电力需求推动着光伏产业向产能高速扩张的方向发展。2001年我国光伏组件产能仅为3MW,而2010年产能预计将达到12.3GW,甚至超过对未来几年线性增长的预期。为了应对如此大规模的增长并满足终端需求,越来越丰富的劳动力资源向光伏行业转移。虽然发展前景乐观,但是为了保证光伏组件生产的稳定性和产品的高品质,需要不断给新手提供工作培训机会,传授生产经验。要保持产能可持续增长,品质必须稳定,这是进一