John D. Meakin

High efficiency CuInSe2 based heterojunction solar cells: Fabrication and results

Abstract A process for fabricating CuInSe2/CdS solar cells is described. A data set of 202 substrates each containing 12 cells from 129 separate deposition runs is used to examine the processing parameters for fabricating high efficiency cells. The data show a broad range of CuInSe2 compositions over which high efficiency cells can be made. The use of a thin CdS layer, less than 2 μm in thickness, can increase the short-circuit current by more than 3 mA cm−2. High efficiency devices have also been made on low cost sodalime glass. Air heat treatments at 200 °C for between 8 and 60 h are required to optimize the output of the CuInSe2/CdS cells.

Thin‐film polycrystalline Cu2S/Cd1−xZnx S solar cells of 10% efficiency

Polycrytalline, thin-film Cu/sub 2/S/Cd/sub 1-x/Zn/sub x/S heterojunction solar cells with conversion efficiencies of 10% have been prepared on Cd/sub 1-x/Zn/sub x/S with 0.1< or =x< or =0.2. Light-generated currents of up to 26 mA/cm/sup 2/ (prorated to 100 mW/cm/sup 2/) have been achieved, comparable to the best observed in Cu/sub 2/S/CdS cells of the same design. The improved performance for Cu/sub 2/S-based devices is as a consequence of the higher open-circuit voltage achieved with the addition of zinc.

Thin-film polycrystalline Cu/sub 2/S/Cd/sub 1-x/Zn/sub x/ S solar cells of 10% efficiency

Polycrytalline, thin-film Cu/sub 2/S/Cd/sub 1-x/Zn/sub x/S heterojunction solar cells with conversion efficiencies of 10% have been prepared on Cd/sub 1-x/Zn/sub x/S with 0.1< or =x< or =0.2. Light-generated currents of up to 26 mA/cm/sup 2/ (prorated to 100 mW/cm/sup 2/) have been achieved, comparable to the best observed in Cu/sub 2/S/CdS cells of the same design. The improved performance for Cu/sub 2/S-based devices is as a consequence of the higher open-circuit voltage achieved with the addition of zinc.

Study of phases formed during production of copper indium diselenide by reacting copper, indium and selenium layers

Abstract CuInSe 2 films were grown by reacting stacked layers of Cu, In and Se in an atmosphere of Se vapor. Incremental growth of the various phases was followed at different temperatures until a single phase CuInSe 2 film was formed. Conventional X-ray diffraction was used in identifying the different phases formed. Along with the knowledge of different phases formed at increasing reaction temperatures, it was concluded that CuInSe 2 is formed at temperatures as low as 235°C, although a single phase film is obtained only at higher temperatures (≈350°C).

Thin film tandem solar cells based on CuInSe2

Abstract The CuInSe 2 /(CdZn)S heterojunction is the best developed low bandgap solar cell for use in a two-junction tandem device. The potential performance of large area terrestrial systems based on this junction is reviewed. A monolithic tandem cell in which the high bandgap cell is a (CdHg) Te/CdS heterojunction deposited onto a CuInSe 2 /(CdZn)S cell is being developed and progress with this system is described.

Formation and characterization of (CdZn)S films and (CdZn)S/Cu2s heterojunctions

The present status of (CdZn)S/Cu2S thin film solar cells is reviewed. A new source design has been used to improve the (CdZn)S films. Light reflection loss has been reduced to ∼ 5% by texturing the (CdZn)S surface prior to Cu2S formation. Using 90% transparent grids, current densities over 16 ma/cm2 and open circuit voltages over 0.7 volts have been obtained, with a best power conversion efficiency of 6.29%.

Degradation of monumental bronzes

Abstract Under the United States National Acid Precipitation Assessment Program a metallurgical and corrosion study has been made of sample of the 50 bronze replicas of the Hiker statue cast by the Gorham Foundry, Providence, Rhode Island, between 1906 and 1966. To study corrosion damage on a microscopic scale a technique was developed to take molds of selected features on the statue. The molds were examined by optical and scanning electron microscopy and surface profilometry. The overall approach has the potential for quantitatively monitoring the local corrosion at selected sites over a period of years and also characterizing the impact of conservation procedures. In a parallel research program, run-off samples were taken from selected Brigade Markers in a series of bronze tablets in the Gettysburg National Military Park; parallel rainwater samples were collected. Analysis for pH, metal content and various ion species in the run off yields information on the total rate of corrosion as a function of dry and wet precipitation.

Status Of CuInSe2 Solar Cells

CuInSe2 has unique optical and electronic properties which make it a prime candidate for low-cost high efficiency thin-film polycrystalline solar cells. Within a decade of the first experiments with thin-film solar cells efficiencies had exceeded 10% and already pre-commercialization efforts are underway. The status and prospects of single junction CuInSe2 based solar cells are reviewed and the potential extension into multijunction configurations considered.

Low Cost Thin-Film CdS-Based Solar Cells—Progress and Promise

The direct conversion of sunlight to electricity using thin film solar cells is potentially a low cost renewable source of energy. A major factor contributing to the low projected costs is the very small quantities of materials required as the active layers of the cells can be as little as 2 μm thick. The efficiency of solar cells will have to exceed ten percent to achieve economic power generation. Until 1976 no thin film solar cells with above seven percent efficiency in sunlight had been reported, but since then the Institute of Energy Conversion has successively reported 7.8, 8.55 and 9.15 percent. This paper will describe the loss minimization methodology utilized to achieve these increases in performance. Analysis shows that efficiencies as high as 14–16 percent for CdS-based solar cells are achievable. The research and development necessary to achieve these high efficiencies will be described. The feasibility of an extremely low cost manufacturing process capable of producing solar cells costing 250 dollars/kWatt will be discussed. Recent progress in development of low-cost thin-film devices shows great promise that direct conversion of sunlight to electricity can make a measurable contribution to the electrical energy supply both nationally and internationally.

AlxGa1−xSb window layers for InGaAsSb/GaSb thermophotovoltaic cells

We report results of a comparative study of AlSb-based window layers for InGaAsSb/GaSb TPV cells made by liquid-phase epitaxy (LPE). Previous work has shown that an AlGaAsSb window layer significantly improves the performance of InGaAsSb/GaSb TPV cells. As expected, the window layer enhances short-wavelength spectral response and increases the open-circuit voltage by reducing the reverse-saturation current of the diode. We present results for a simpler alternative window layer based on the ternary AlGaSb alloy. We fabricated, characterized, and compared InGaAsAsSb TPV of three types: 1. with an AlGaAsSb window layer, 2. with an AlAsSb window layer, and 3. with no window layer. Both p-on-n (p-type InGaAsSb emitter; n-type InGaAsSb base) and n-on-p (n-type InGaAsSb emitter; p-type InGaAsSb base) homojunction cell configurations were investigated. The InGaAsSb layers have a ∼0.55-ev bandgap and are lattice-matched to a GaSb substrate. As anticipated, both AlGaSb and AlGaAsSb passivated TPV cells were superio...