摘要:

CdTe/CdS heterojunction thin film solar cells of 11.7% efficiency have been made by close-spaced sublimation of CdTe. Some results regarding the influence of the CdCI2treatment and contacting are given stressing the requirement of more in-depth analysis of the CdTe cells made by different processes in order to understand the common and basic mechanisms better.

ISSN:0142-5919    

DOI:10.1080/01425919208909756

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Atomic Layer Epitaxy, ALE, has been applied to grow CdS/CdTe-thin film solar cells. ALE offers the possibility to grow both CdS and CdTe in a single process and to taylor the interface of CdS and CdTe. The thickness of CdS was varied and the optimum was found to be in the range of 50-100 nm with good heterojunction performance and CdTe-crystallinity leading to excellent PV-properties. The structures with thinner CdS layers suffered low open circuit voltage but on the other hand with thicker CdS the short circuit current was limited by the absorption of CdS.

ISSN:0142-5919    

DOI:10.1080/01425919208909757

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

By analyzing CdTe/CdS devices fabricated by vacuum evaporation, a self consistent picture of the effects of processing on the evolution of CdTe cells is developed which can be applied to other fabrication methods. In fabricating CdTe/CdS solar cells by evaporation, a 400°C CdCI2heat treatment is used which recrystallizes the CdTe and interdiffuses the CdS and CdTe layers. The interdiffuson can change the bandgap of both the CdTe and CdS which modifies the spectral response of the solar cell. After this heat treatment a contacting/doping procedure is used which converts the CdTe conductivity to p-type by diffusion from Cu from the contact. Finally, the cell is treated with Br2CH3,OH which improves both Voc and FF. Analogous process steps are used in most fabrication processes for CdTe/CdS solar cells.

ISSN:0142-5919    

DOI:10.1080/01425919208909758

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We review the use of laser-driven physical vapor deposition from solid targets for the growth of CdTe-related photovoltaic materials on glass substrates. The physical conditions in the laser-driven plume from 15 nsec pulses at λ = 308 nm from an XeCI laser have been studied by optical multichannel spectroscopy and time-of-flight methods. Film growth has been optimized in terms of substrate temperature, laser pulse energy density, and overall growth rate through the use of optical absorption, Raman scattering, x-ray diffraction, electron microscopy, energy dispersive x-ray spectroscopy, and electrical measurements on the films. Early results of device fabrication have yielded an all-LDPVD CdS/CdTe cell of 8.7% AM 1.5 efficiency.

ISSN:0142-5919    

DOI:10.1080/01425919208909759

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The stacked elemental layer (SEL) technique has been used to synthesise thin films of CdTe. This technique consists of depositing alternate layers of Cd/Te in the stoichiometric ratio and then annealing the stack to react the layers to form the compound. The Cd and Te layers were deposited using thermal evaporation and annealed in nitrogen, vacuum or air. Transmittance and reflectance data, X-ray diffraction data and scanning electron microscopy observations of the surface topology are given for the layers produced. Post synthesis annealing of the layers using CuCl2/CdCl2/methanol was also investigated. This was found to substantially increase the grain size of the layers produced. This process promises to be a low cost method for producing large areas suitable for use in solar cell structures. A preliminary energy analysis has been carried out and energy payback times and energy ratios are presented.

ISSN:0142-5919    

DOI:10.1080/01425919208909760

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A simple new method suitable to grow large crystalline grain CdTe thin films on glass substrates has been developed. CdTe films which exhibit a grain size larger than 20 µm have been obtained. The films are p-type with a resistivity of about 100 Ωcm. Backwall CdTe/CdS thin film solar cells with an efficiency above 9% have been prepared.

ISSN:0142-5919    

DOI:10.1080/01425919208909761

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Heteroepitaxial (111) and (100) oriented CdTe layers have been grown on Si substrates by conventional molecular beam epitaxy (MBE) and photo-assisted MBE (PAMBE) using stacked BaF2-CaF2as a buffer to overcome the 19% lattice mismatch between Si and CdTe. Heteroepitaxial As doped p-type CdTe(lOO) layers have been grown on BaF2-CaF2/Si(100). The dopant activation is accomplished using an extra Cd source and laser illumination of the substrate during growth. The growth kinetics and surface reconstructions have been studied using RHEED during CdTe growth under different conditions, and the induced effects on Te-desorption, Cd-migration, and As-substitution on Te-vacancy site have been correlated. The resistivity of As doped CdTe layers is down to 20 ohm cm. The 8 K photoluminescence spectra of such a layer shows a dominant (A°, X) peak at 1.590 eV and the As acceptor level corresponds to a shallow level with = 60 me V activation energy. A lift-off technique has been used to separate the single crystal CdTe thin films from the Si wafer by dissolving the fluoride buffer. CdS/CdTe solar cells have been fabricated in these layers.

ISSN:0142-5919    

DOI:10.1080/01425919208909762

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

“Art jumps ahead – science plods ponderously on behind to consider, describe, and finally document what “;actually” happened in the chaos of the leap”(ALF)

ISSN:0142-5919    

DOI:10.1080/01425919208909763

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Polycrystalline CdTe thin films have been prepared (using radio frequency (rf) planar magnetron sputtering), characterized, and used to fabricate CdS/CdTe solar cells. The performance characteristics of the best device (as measured under standard reporting conditions) are a conversion efficiency of 8.2% and 0.68 V and 21.7mA/cm2 for open-circuit voltage (Voc) and short-circuit: current density (J), respectively. Photoluminescence emission from the polycrystalline CdTe films (after the high-temperature heat treatment) showed that this material is dominated by four defects, including two donor levels Dl and D2 (at 120 and 180 meV below the conduction band) and two acceptor levels Al and A2 (at 30 and 65 meV above the valence band [VB]). Capacitance-voltage (C-V) measurements have indicated the formation of an n-i-p structure dominated by a high density of interface states. Deep level transient spectroscopy (DLTS) data also confirmed a minority electron trap at about 1.212 meV below the conduction band (CB) dominating the CdTe device. The trap level detected in a Schottky barrier, fabricated on a CdTe film without heating at high temperature, is deeper and higher in density than that in the heterojunction. This explains the enhancement of the Voc of the heterojunction devices after annealing at 400°C or higher. Although the device performance is modest by comparison with state-of-the-art devices, these results support the potential of sputter depositing CdTe films as a production technique. Considerable work must still be done to improve the material quality and reduce the density of defect levels.

ISSN:0142-5919    

DOI:10.1080/01425919208909764

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The structural and electrical properties of the epitaxial CdS-CdTe heterostructures are reviewed. Both CdS epitaxial layers grown on CdTe substrates and CdTe layers on CdS substrates are discussed. In both systems epitaxy appears to be dependent on the substrate polarity, with the best epitaxy occurring on the non-metal polar surfaces. Current transport is controlled by a multi-step tunneling/recombination process in both types of structure. The photovoltaic characteristics of CdS layers on CdTe substrates are dominated by the high bulk resistance of the CdTe. The photovoltaic properties of the CdTe layers on CdS substrates are less affected by substrate resistance (since the CdS substrates are generally more conducting) but are limited by greater junction losses resulting in lower open circuit voltages.

ISSN:0142-5919    

DOI:10.1080/01425919208909765

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor