Solar Cells最新文献

Federal and state agencies have classified cadmium and selenium compounds as hazardous. Consequently, facilities using these materials are subject to various regulations and guidelines developed by these agencies. The intent of these guidelines is to protect worker and public health from accidental and routine chemical exposures. In this context, the agencies provide specific limits on public and occupational exposures, and generalized guidance on methods or approaches for attaining such limits. This paper gives background information on the toxicology and pharmacology of cadmium and selenium compounds, and reviews several newly proposed or adopted Federal and state regulations which can affect photovoltaic manufacturing facility operations using these and other similar chemicals.

Atomic layer epitaxy (ALE) was used to grow several components of the cascade solar cell structure in the AlGaAs/GaAs system. An ALE reactor was constructed for multiwafer growth with a growth rate of 0.6 μm h⁻¹. Device quality GaAs and $\text{As}{}_{\mathrm{x}}\text{Ga}{}_{\mathrm{1-x}}\text{As}$ films were grown with p-type background carbon doping in the ranges 10¹⁵–10¹⁹ cm⁻³ and 10¹⁶–10²⁰ cm⁻³ respectively. N-type films were achieved by SiH₄ doping, producing carrier concentrations in the range 10¹⁶–10¹⁸ cm⁻³. In addition, the potential applications of the ALE technique in the photovoltaic field are discussed.

II–VI semiconductors and their alloys are promising thin film photovoltaic materials. Polycrystalline films of cadmium telluride (CdTe), zinc telluride (ZnTe), cadmium zinc telluride ($\text{Cd}{}_{\mathrm{x}}\text{Zn}{}_{\mathrm{1-x}}\text{Te}$), and mercury zinc telluride ($\text{Hg}{}_{\mathrm{x}}\text{Zn}{}_{\mathrm{1-x}}\text{Te}$) were deposited onto glass and transparent-conducting-semiconductor (TCS) coated glass substrates by metal-organic chemical vapor deposition. Emphasis was directed to the doping of CdTe films, ohmic contacts to p-CdTe, and thin film CdTe homojunctions. CdTe films may be doped intrinsically or extrinsically; gallium and arsenic were used as the extrinsic n and p dopant respectively. p⁺-ZnTe films deposited in situ were used as an ohmic contact to p-CdTe films. Thin film CdTe homojunctions were prepared by the successive in situ deposition of n-CdTe, p-CdTe, and p⁺-ZnTe films on SnO₂-coated glass substrates, and their properties were investigated. The properties of $\text{Cd}{}_{\mathrm{x}}\text{Zn}{}_{\mathrm{1-x}}\text{Te}$ and $\text{Hg}{}_{\mathrm{x}}\text{Zn}{}_{\mathrm{1-x}}\text{Te}$ films with band gap energy in the range 1.65–1.75 eV deposited onto glass and TCS-coated glass substrates were studied.

In this paper, we discuss various aspects of the development of an inverted-grown AlGaAs/GaAs cascade solar cell incorporating a patterned germanium tunnel junction. Topics include the development of the Al_0.37Ga_0.63As top cell, the growth of the GaAs bottom cell over the patterned germanium tunnel junction, and a technique for selective removal of thin AlGaAs/GaAs heterostructures after lattice-matched growth of germanium substrates. The problems to be overcome for the achievement of around 30% efficiencies in the AlGaAs/GaAs cascade cell under concentrator applications are also discussed.

During the research stage, many photovoltaic solar cells suffer substantial power loss due to the use of non-optimum top contact grids. The very nature of solar cell research implies that many cell parameters will be in a continual state of change and thus the grid will seldom be truly optimized. However, several things can be done to ensure that a solar cell grid will perform well even if the parameters vary. In this paper, critical parameters for solar cell grid modeling and design are identified and discussed. Particular attention is paid to the manner in which process aspects affect these parameters and the subsequent power loss of the grid. Finally, practical guidelines are presented, the use of which can minimize the effect of process variation.

Using tandem cell test units with GaAs and GaSb concentrator cells, we have achieved a NASA verified conversion efficiency of 30.8% for space applications. Here, we describe tandem gallium cell assemblies and flex circuit tape interconnect concepts for use in practical power generating concentrator panels. The forward and reverse characteristics of tandem cell voltage-matched circuits are described. It is noted that the GaSb IR cell doubles as a bypass diode, providing shading protection for the GaAs cell.

The availability of commercial spectroscopic ellipsometers (SE) has been restricted to the UV-visible range from 250–900 nm. Although this is useful for many applications, it must be extended to the near IR region (up to 1700 nm) for the study of the optical behavior of most photovoltaic materials. This paper discusses the development of a broad band (300–1700 nm) SE which has been used to measure the optical characteristics of various materials. Among these are the polycrystalline thin film materials, CuInSe₂ and CdTe (for which single crystal samples have also been investigated), and materials for high efficiency cascade solar cells including InP, InGaAs and InGaAsP. Most of these data are not presently available over such a wide spectral range.

Experimentally, a rotating polarizer-fixed analyzer ellipsometer with an a.c. detection system has been developed for accurate measurement of ψ and Δ, the relevant ellipsometric parameters, in the near IR. This approach has certain advantages over the rotating analyzer-fixed polarizer systems including reduced sensitivity to room light. The analytical methods include the use of a specially developed computer modeling program which gives ψ and Δ for a given set of values related to the film thickness (which may be finite or zero) and to the optical properties of the substrate.

We present a summary of our defect chemical microscopic model for the effect that annealing in air or oxygen has on CuInSe₂ and CdTe-based polycrystalline thin film solar cells and explain its generalization to other chalcogenide-based semiconductor devices. The summary includes a hypothesis for specific O₂ (molecule) and surface interaction. From the point of view of device performance, the model provides a specific chemical explanation for the conclusions obtained from device analyses that the performance of the present generation of polycrystalline cells of this type is mainly limited by recombination at grain surfaces and boundaries.