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One of the key requirements to achieve solar conversion efficiencies greater than 50% is a photovoltaic device with a band gap of 2.4 eV or greater. lnxGa1-xN is one of a few alloys that can meet this key requirement. InGaN with indium compositions varying from 0 to 40% is grown by both metal-organic, chemical-vapor deposition (MOCVD) and molecular beam epitaxy (MBE), and studied for suitability in...
We show how semiconductor quantum dots may greatly increase photon conversion efficiencies by producing multiple excitons from a single photon. This is possible because quantization of energy levels in quantum dots enhances Auger processes, eliminates the requirement to conserve crystal momentum, and thus promotes multiple exciton generation, Quantum yields of 300% for exciton formation in PbSe, PbS,...
It is known that solar cells with high current, based on materials of low band gap, present low voltages and vice-versa. Intermediate band (IB) solar cells have been proposed as a means of increasing the current of solar cells without a substantial decrease of the voltage. The present status of the research on this topic is presented. IB materials and the related solar cells have been manufactured...
Results of quantum calculations in M-doped chalcopyrite Cu4 MGa3S8 (with M=Ti, V, Cr or Mn) are evaluated. The purpose of this work is the quest of a compound which possesses an isolated narrow partially-filled electronic band sited into the host semiconductor bandgap. The aforementioned material could be useful for designing novel solar cells with very high efficiency. Density functional theory calculations...
The strain balanced quantum well solar cell (SB-QWSC) provides a novel method of engineering the bandgap of a p-i-n junction to better match the terrestrial solar spectrum. The ability to accurately model the spectral response of a SB-QWSC is vital in optimising cell design. We present a study into two major components of such a model. Firstly, we provide an overview of the model for the confined...
The film quality improvement of amorphous carbon (a-C) layers for C60/a-C superlattice solar cells has been intended. a-C:N films were deposited by C60-cage breaking, and the layer-by-layer hydrogen treatment method was applied to the a-C:N films for the improvement of the film quality, and the structural change by the hydrogen treatment was investigated. Hydrogen radicals reconstruct carbon bonding...
The fundamental efficiency of a photovoltaic device is ultimately constrained by the temperature difference between the sun and the PV device. An ideal "Shockley-Queisser" single junction solar cell shows both a rise in limiting efficiency and reduction in optimum band-gap energy as the cell temperature is reduced. In the case of a solar cell that is dominated by parasitic non-radiative...
Luminescent concentrators may have significant promise for producing low-cost PV energy. Luminescent concentrators convert the solar spectrum and concentrate the sunlight, but the benefit that can be obtained by the spectral conversion is not obvious. This paper presents the results of a theoretical study of the impact of spectral concentration. A well-known set of relationships for PV cell efficiency...
We have theoretically analyzed the potential efficiency improvement to multi-junction solar cell efficiencies which are available through the incorporation of quantum dot using detailed balance calculations. We have also experimentally investigated the Stranski-Krastanov growth of self-organized InAs quantum dots and quantum dot arrays on lattice-matched GaAs by metallorganic vapor phase epitaxy (MOVPE)...
Photoactive nanomaterials are being investigated as multifunctional additives in polymeric photovoltaic devices. Polymer photovoltaic devices which rely solely on photon absorption by the conducting polymer are bandgap-limited (typically > 2 eV) with regard to the solar spectrum. Therefore, nanomaterials with optical absorption below the conducting polymer bandgap can allow composite devices to...
Concepts of bulk sensitization of inorganic semiconductors by organic dye molecules either to increase the absorptivity of indirect semiconductors as μc-Si or to expand in a two photon process the absorption spectrum of wide gap semiconductors to photons of energy below the band gap are introduced. Hybrid composites have been prepared in vacuum by combining CVD and PVD thin film growth methods. Raman...
An approach to third-generation solar cells with a much better figure of merit, i.e., the efficiency/cost ratio, is proposed. It combines the advantages of low-cost wet-chemical fabrication and high-efficiency inorganic crystalline solar cells. The materials which allow wet-chemical fabrication of inorganic crystalline solar cells are semiconducting metal oxides. An analysis is presented on the challenges...
The limits of photovoltaic solar energy conversion by fluorescent collectors are examined theoretically and experimentally. The maximum efficiency of a fluorescent collector corresponds to the Shockley-Queisser limit for a non-concentrating solar cell with a single band gap energy. To achieve this efficiency, the collector requires a photonic structure at its surface that acts as an omnidirectional...
Quantum dot solar concentrators (QDCs) have been fabricated by the incorporation of quantum dots into highly transparent polymer host materials. UV polymerisation techniques were found to reduce the quantum dot quantum efficiency in comparison with thermally polymerised samples. The sample plates were characterised using photocurrent techniques in individual and stacked configurations. Due to the...
Cd1-xMgxTe is a potential candidate for the top cell in two-terminal tandem solar cells. The close match of the lattice constant of MgTe with CdTe and the apparent complete miscibility of MgTe in CdTe and the rapid increase in band gap with Mg content gives flexibility to prepare material with the appropriate band gap for current-matching in a tandem solar cell. We have chosen to deposit Cd 1-xMgx...
We have used electronic and optical techniques to characterize alloys of the Cu(ln,Ga)(S,Se)2 material system. The alloys were prepared such that the bandgap of the resultant materials was near 1.5 eV. These materials are interesting as the absorber layer of thin-film solar cell devices, and were studied in a solar cell device configuration. Electronic characterization techniques included admittance...
We report on the progress in fabricating CIGS solar cells where the absorber thickness is nominally about 1-mum. This is done with the objective of reducing the material cost in large-volume production of CIGS where the cost of the high-purity metals, and especially that of In, will become significant factors. At the present time, we have fabricated a 17.1% efficient solar cell for a 1-mum thick CIGS...
Real time spectroscopic ellipsometry (RTSE) has been applied to characterize process-property relations in polycrystalline CdTe films prepared to 3000 Aring by magnetron sputtering under conditions similar to those yielding 14%-efficient solar cells. In this study, the key process variable is the deposition temperature (T: 188lesTles304 degC), which was calibrated in situ from the CdTe E0 band gap...
CdS films were deposited with chemical bath deposition (CBD) onto Cu(In,Ga)Se2/Mo/soda-lime glass structures. The basic ingredients for the CBD were ammonia (NH4OH), cadmium acetate (CdAc), and thiourea CS(NH2)2. Two recipes with very low thiourea concentration were compared to the baseline recipe. From quantum efficiency measurements we observe an increased carrier collection for longer wavelengths...
Cadmium sulfide thin films have been grown using a modified chemical bath deposition method with four innovative features: i) ethylenediamine was used as the complexing agent, enabling the use of low cadmium concentrations, ii) a rectangular bath geometry with heated glass plate walls was employed, iii) a low deposition temperature (30degC) was used and iv) nitrogen gas was flowed over the substrate...
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