Solar Cells For Terrestrial Applications Research Articles

Optoelectronic optimization of graded-bandgap thin-film AlGaAs solar cells.

An optoelectronic optimization was carried out for an $ {{\rm Al}_\xi }{{\rm Ga}_{1 - \xi }}{\rm As} $AlξGa1-ξAs (AlGaAs) solar cell containing (i) an $ n $n-AlGaAs absorber layer with a graded bandgap and (ii) a periodically corrugated Ag backreflector combined with localized ohmic Pd-Ge-Au backcontacts. The bandgap of the absorber layer was varied either sinusoidally or linearly. An efficiency of 33.1% with the 2000-nm-thick $ n $n-AlGaAs absorber layer is predicted with linearly graded bandgap along with silver backreflector and localized ohmic backcontacts, in comparison to 27.4% efficiency obtained with homogeneous bandgap and a continuous ohmic backcontact. Sinusoidal grading of the bandgap is predicted to enhance the maximum efficiency to 34.5%. Thus, grading the bandgap of the absorber layer, along with a periodically corrugated Ag backreflector and localized ohmic Pd-Ge-Au backcontacts, can help realize ultrathin and high-efficient AlGaAs solar cells for terrestrial applications.

Numerical simulation of the temperature distortions in InGaP/GaAs/Ge solar cells working under high concentrating conditions due to voids presence in the solder joint

The presence of voids in solar cell solder joints causes a modification of the heat fluxes inside the device during its operation, which in turn leads to local increases in cell temperature and thermal resistance. These temperature increases at device surface lead to a modification of the photovoltaic cell voltage map which translates in a drop in cell output power. Moreover, for pv cells working under high concentration conditions such as III–V multi-junction solar cells for terrestrial application, very high temperature increases can arise as a consequence of void presence, both above the void volume and around it, leading in extreme cases to irreversible damages of the device. In this paper a matlab script is implemented to assess the temperature increase at the top surface of a InGaP/GaAs/Ge solar cell, in the device regions lying outside the void coverage area, for different void sizes found in concentrator solar cells. The obtained results are compared to those of finite element method (FEM) simulations, which are based on an equivalent 2.5 D thermal representation of the cell. A good agreement between FEM simulations and the developed thermal model is observed for small and medium size voids, while for larger voids the error between FEM simulations and the developed model becomes not-negligible. An analytical expression is obtained to assess the device thermal resistance in presence of a random distribution on not-interacting voids. The developed model can be used as starting point to assess the influence of void presence on the power performances of InGaP/GaAs/Ge multi-junction solar cells working under high concentrating conditions.

Optimized multi-junction photovoltaic solar cells for terrestrial applications

Sunlight, undoubtedly, is the future source of energy for humans. The current conversion technologies of sunlight to electricity using photovoltaic technologies are still moderate and relatively costly. The multi-junction photovoltaic cell design offers the highest achieved conversion efficiency that already exceeded the 40%. This work aims for maximizing the conversion of the sunlight for terrestrial application using the series-multi-junction photovoltaic cells by an optimal choice for the bandgap energies.

Influence of window layer thickness on double layer antireflection coating for triple junction solar cells

The optimization of a SiO2/TiO2, SiO2/ZnS double layer antireflection coating (ARC) on Ga0.5In0.5P/In0.02Ga0.98As/Ge solar cells for terrestrial application is discussed. The Al0.5In0.5P window layer thickness is also taken into consideration. It is shown that the optimal parameters of double layer ARC vary with the thickness of the window layer.

Copper (I) oxide (Cu<sub>2</sup>) based solar cells - a review

Copper (I) oxide (Cu2O) is a potential material for the fabrication of low cost solar cells for terrestrial application. A detailed survey on the previous work so far carried out on Cu2O based solar cells has been presented. The aspects discussed include the fabrication of Schottky (metal/semiconductor) barrier Cu2O solar cells, where different low work function metals are used to form the Schottky barrier solar cells. The problems associated with the Cu2O Schottky barrier solar cells and efforts made at improving the performance of these solar cells are highlighted. Discussions on heterojunction solar cells with Cu2O have also been presented. Various transparent conducting oxides (TCOs) used in forming the heterojunction cells are mentioned, and successes and failures of using them highlighted. The technological developments of these cells are still in their infancy and the performance remains very poor. The root causes of this poor performance are analyzed and possible areas for future research in the field are outlined. Keyword: Copper (I) oxide, Solar cells, Solar cells, Schottky barrier sola cells

Effect of Au contamination on the electrical characteristics of a “model” small-angle grain boundary in n-type direct silicon bonded wafer

We have investigated the electrical characteristics of a “model” small-angle grain boundary (GB) in n-type direct silicon bonded wafers with intentional Au contamination. It is found that the Au aggregated at the GB can cause new acceptorlike states, developing a potential barrier. The density of Au-related GB states is about 1–2×1012 cm−2 eV−1 in the energy range of Ec-0.65–Ec-0.33 eV. With the energy level becoming deeper, the corresponding electron capture cross-section becomes larger, in the order of magnitude 10−16–10−15 cm2. It is believed that Au contamination has strong influence on the electrical properties of GB. These results are interesting for the GB engineering of n-type multicrystalline silicon solar cells for terrestrial application.

A Novel Poly-Si Solar Cell using Grain Boundary Etching Treatment and Transparent Conducting Oxide

ABSTRACTThis paper deals with a novel structure of polycrystalline silicon (poly-Si) solar cell for terrestrial applications. Grain boundary (GB) in poly-Si degrades a conversion efficiency of poly-Si solar cell. To reduce the GB side-effect, we investigated various parameters such as the preferential GB etch, etchtime, ITO electrode, heat treatment, and emitter layer effect. Among various preferential etchants such as Sirtl, Yang, Secco, and Schimmel, a Schimmel etchant illustrated an excellent preferential etching property. We observed a 10μm deep trench along grain boundaries and randomly textured grain surface with pyramid structure. We used rf magnetron sputter grown tin doped indium oxide (ITO) film as a top contact metal. ITO films showed a resistivity of 1.14 ×10-4 Ω-cm and transmittance of 90.5% for the wavelength of 594 nm. ITO films served as a top electrode as well as an effective AR coating layer. ITO film properties were strongly influenced by the preparation temperatures. Substrate temperature of 400oC gave the highest conversion efficiency of poly-Si solar cell. With well-fabricated poly-Si solar cells, we were able to achieve conversion efficiency as high as 16% at the input power of 20 mW/cm2.

III-Vs advance on silicon

With a plentiful (and free) supply of 1 kW/m 2 of sunlight at the earth's surface, the market for solar cells for terrestrial applications is expected to expand rapidly as the cost of power from conventional sources rises and, due to technology advances and economies of scale, the cost of solar cells falls. So far most cells have been made of single-crystal silicon. However, GaAs currently holds the efficiency record for single-junction photovoltaic cells [I], with further advances using other III-Vs being made.

Electrodeposition of copper-indium alloy under diffusion-limiting current control

The aim of this work was to study a method of electrodeposition of stoichiometric copper-indium alloy to be used as a precursor for obtaining CuInSe 2 by selenization. This compound represents one of the most promising materials in terms of low cost and high efficiency for the realization of large-area thin film solar cells for terrestrial applications. However, to avoid the growth of secondary phases such as CuSe and In 2Se 3, the stoichiometry and morphology of the alloy have to be carefully controlled. We investigated the relationship between the ratio of Cu 2+ to In 3+ in the solution and the metal ratio in the deposited film. In order to avoid the use of complexing agents we chose to control the stoichiometry of the copper-indium alloys, electrodepositing them under diffusion-limiting current. Since the diffusion currents are, as a first approximation, proportional to the concentrations, there is a simple relationship between the individual diffusion currents of the ions and the stoichiometry of the deposited alloy. Thus we can change the CuIn content in the deposited film by controlling the ratio between the ions in the deposition bath.

Cu 2O solar cells: A review

The status of Cu 2O solar cells is reviewed. Cu 2O is a potential material for the fabrication of solar cells for terrestrial application particularly as the top cell in a cascade cell structure. The technological development of the cells, however, is still in its infancy performance remains very poor. An analysis of the causes of this poor performance is given and possible areas for future research in the field are outlined.

Epitaxial films grown by vacuum MOCVD

We are developing high efficiency multicolor solar cells for terrestrial applications using a novel MOCVD growth technique, vacuum MOCVD, for growing the sequential epitaxial layers. We believe the vacuum MOCVD growth technology offers several advantages for production scale-up including the more efficient use of the metal alkyl source materials. In addition, the use of stainless steel rather than glass offers important safety advantages. For two color cell applications, we are currently developing the GaAs 1− x P x and GaAs 1− y Sb y ternary alloys. In this paper, we first describe our vacuum MOCVD system and then the current status of our vacuum MOCVD grown GaAs 1− y Sb y materials. Triethyl-Sb and trimethyl-Sb are compared as sources of Sb, and dicyclopentadienyl-Mg and diethyl-Zn are compared as p-type dopant sources

Use of tin oxide as an inexpensive antireflection coating for p on n polycrystalline silicon solar cells

The potential of tin oxide as an inexpensive antireflection (AR) coating for polycrystalline silicon solar cells has been investigated. Undoped tin oxide films of a desired thickness were deposited over p on n polycrystalline silicon solar cells by spray pyrolysis of an alcoholic solution of hydrated stannic chloride at 500°C. Evaluation of cell performance before and after this AR coating showed that the AR coating is highly compatible with the polycrystalline silicon solar cells. About 40-50 percent improvement in the short-circuit current of p on n polycrystalline cells has been measured. The coating may be highly suited to large-scale production of low-cost polycrystalline silicon solar cells for terrestrial application.

Die Silicium-Solarzelle f�r terrestrische Anwendungen

The direct conversion of solar energy to electrical energy (photovoltaic effect) by solar cells is receiving increasing attention on a world-wide scale. Photovoltaic energy conversion offers itself to a practical and meaningful implementation in regions without a conventional energy grid. This paper deals with the principles of silicon solar cells for terrestrial applications and new methods for the production of the necessary silicon.

Cr-MIS solar cells using thin epitaxial silicon grown on poly-silicon substrates

Cr-MIS solar cells were fabricated on 18-30 µm epitaxial-Si layers grown on poly-Si substrates. Solar conversion efficiency values ranged from an average of 8.8% to 4.0% depending on choice of substrate. Nonuniformity of certain substrates led to low efficiency values. Interface state density > 5 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">12</sup> /cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> -eV contributed to low V <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">oc</inf> and high n-factor. Low minority carrier diffusion length caused J <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">sc</inf> to drop to 60% of the optimum value. Substrates with imperfections caused an increase in dark current density by three orders of magnitude, which served to decrease photovoltaic response. The procedures given herein could lead to a low-cost solar cell for terrestrial applications.

Silicon films on foreign substrates for solar cells

Silicon films on foreign substrates have been used for various device applications for over fifteen years. The current interest in the photovoltaic conversion of solar energy for terrestrial applications has stimulated investigations on the feasibility of using polycrystalline silicon films on low cost substrates for solar cell purposes. In this paper, the deposition and properties of silicon films on several low cost substrates, such as steel, aluminum, graphite, and metallurgical silicon, are reviewed. The characteristics of solar cells prepared from these films are discussed. The present results indicate that the deposition of a silicon film containing a p-n junction on a purified, recrystallized metallurgical silicon substrate is a promising approach for the fabrication of low-cost solar cells for terrestrial applications.

Silicon solar cells for terrestrial applications

The ways in which silicon solar cells can be designed to give maximum efficiency are reviewed. It is suggested that, although the reduction of processing costs is an extremely important objective of the development programme aimed at widespread application in highly developed countries, the improvement of design might have sufficient cost benefit even if based on current processing technology for the application of solar cells in remote localities which are not easily served with electricity via transmission lines.

Design of solar cells for terrestrial use

The various aspects that must be considered to successfully design solar cells for terrestrial systems are presented. Some of the more recent developments in solar cell technology are mentioned. It is concluded that the most logical approach to the use of silicon solar cells for terrestrial applications is to utilize solar concentrators in conjunction with cells specially designed for such operations. The factors that affect solar-cell performance are discussed, and an experiment is described that optimizes the most important parameters for obtaining the best performance at intensities of between 100 and 400 milliwatts per square centimeter. The characteristics of such optimized cells are compared with the more common cell designs with regard to the various electrical parameters. A discussion of cell-concentrator systems is presented and some cost estimates are given.

Use of concentrated sunlight with solar cells for terrestrial applications

Methods for obtaining less-expensive power generation from sunlight are described. The use of large area solar cells in conjunction with simple, conical concentrators indicate that costs can be decreased by a factor of five compared to present-day bare solar-cell systems. The solar cells used in this experimental concentrator system were specially designed to operate at high intensities. The concentrator system was designed to operate efficiently with no auxiliary cooling equipment and to produce about one-half watt per cell, or about three times the bare solar cell output. Experimental voltage-current characteristic curves for the system were obtained under equilibrium temperature conditions. The effects of sun angle of incidence on system performance was also determined.