Comparative radiation testing of solar cells for the shuttle power extension package

The Power Extension Package (PEP) is the prime focus of a development program to produce low cost solar cells. The PEP is a 32 kilowatt flexible substrate, retrievable, solar array system for use on the Space Shuttle. Solar cell cost will be reduced by increasing cell area and simplifying cell and coverglass fabrication processes and specifications. The cost goal is to produce cells below $30 per watt. Two and ten ohm-cm silicon cells were investigated. This paper describes a unique radiation damage test and side-by-side comparison of candidate cell types with pre-and post-irradiation airplane calibration of outer space short-circuit current

Preliminary evaluation of Glass Resin materials for solar cell cover use

The glass resins were deposited by several techniques on 200 micron thick cells and on 50 microns thick wafers. The covered cells were exposed to ultraviolet light in vacuum to an intensity of 10 UV energy-equivalent solar constants at air mass zero for 728 hr. The exposure was followed by a single long thermal cycle from ambient temperature to -150 C. Visual inspection of the samples indicated that all samples had darkened to varying degrees. The loss in short-circuit current was found to range from 8 to 24%, depending on the resin formulation. In another test over 40 glass resin-coated silicon wafers withstood 15 thermal cycles from 100 to-196 C in one or more of the thicknesses tested. Several of the resin-coated wafers were tested at 65 C and 90% relative humidity for 170 hr. No change in physical appearance was detected

Temperature and intensity dependence of the performance of an electron-irradiated (AlGa)As/GaAs solar cell

The performance of a Hughes, liquid-phase epitaxial 2 centimeter-by-2 centimeter, (AlGa)As/GaAs solar cell was measured before and after irradiations with 1 MeV electrons to fluences of 1 x 10 to the 16th power electrons/sq cm. The temperature dependence of performance was measured over the temperature range 135 to 415 K at each fluence level. In addition, temperature dependences were measured at five intensity levels from 137 to 2.57 mW/sq cm before irradiation and after a fluence of 1 x 10 to the 16th power electrons/sq cm. For the intermediate fluences, performance was measured as a function of intensity at 298 K only

Performance of epitaxial back surface field cells

Epitaxial back surface field structures were formed by depositing a 10 micron thick 10 Omega-cm epitaxial silicon layer onto substrates with resistivities of 0.01, 0.1, 1.0 and 10 Omega-cm. A correlation between cell open-circuit voltage and substrate resistivity was observed and was compared to theory. The cells were also irradiated with 1 MeV electrons to a fluence of 5 X 10 to the 15th power e/cm2. The decrease of cell open-circuit voltage was in excellent agreement with theoretical predictions and the measured short circuit currents were within 2% of the prediction. Calculations are presented of optimum cell performance as functions of epitaxial layer thickness, radiation fluence and substrate diffusion length

Performance and temperature dependencies of proton irradiated n/p GaAs and n/p silicon cells

The n/p homojunction GaAs cell is found to be more radiation resistant than p/nheteroface GaAs under 10 MeV proton irradiation. Both GaAs cell types outperform conventional silicon n/p cells under the same conditions. An increase temperature dependency of maximum power for the GaAs n/p cells is attributed largely to differences in Voc between the two GaAs cell types. These results and diffusion length considerations are consistent with the conclusion that p-type GaAs is more radiation resistant than n-type and therefore that the n/p configuration is possibly favored for use in the space radiation environment. However, it is concluded that additional work is required in order to choose between the two GaAs cell configurations

Indium phosphide solar cell research in the US: Comparison with nonphotovoltaic sources

Highlights of the InP solar cell research program are presented. Homojunction cells with AMO efficiences approaching 19 percent were demonstrated while 17 percent was achieved for indium tin oxide (ITO)/InP cells. The superior radiation resistance of these latter two cell configurations over both Si and GaAs were demonstrated. InP cells on board the LIPS III satellite show no degradation after more than a year in orbit. Computer modeling calculations were directed toward radiation damage predictions and the specification of concentrator cell parameters. Computed array specific powers, for a specific orbit, are used to compare the performance of an InP solar cell array to solar dynamic and nuclear systems

Potential for use of indium phosphide solar cells in the space radiation environment

Indium phosphide solar cells were observed to have significantly higher radiation resistance than either GaAs or Si after exposure to 10 MeV proton irradiation data and previous 1 MeV electron data together with projected efficiencies for InP, it was found that these latter cells produced more output power than either GaAs or Si after specified fluences of 10 MeV protons and 1 MeV electrons. Estimates of expected performance in a proton dominated space orbit yielded much less degradation for InP when compared to the remaining two cell types. It was concluded that, with additional development to increase efficiency, InP solar cells would perform significantly better than either GaAs or Si in the space radiation environment

GaAs homojunction solar cell development

The Lincoln Laboratory n(+)/p/p(+) GaAs shallow homojunction cell structure was successfully demonstrated on 2 by 2 cm GaAs substrates. Air mass zero efficiencies of the seven cells produced to date range from 13.6 to 15.6 percent. Current voltage (I-V) characteristics, spectral response, and measurements were made on all seven cells. Preliminary analysis of 1 MeV electron radiation damage data indicate excellent radiation resistance for these cells

Voltage controlling mechanisms in low resistivity silicon solar cells: A unified approach

An experimental technique capable of resolving the dark saturation current into its base and emitter components is used as the basis of an analysis in which the voltage limiting mechanisms were determined for a variety of high voltage, low resistivity silicon solar cells. The cells studied include the University of Florida hi-low emitter cell, the NASA and the COMSAT multi-step diffused cells, the Spire Corporation ion-implanted emitter cell, and the University of New South Wales MINMIS and MINP cells. The results proved to be, in general, at variance with prior expectations. Most surprising was the finding that the MINP and the MINMIS voltage improvements are due, to a considerable extent, to a previously unrecognized optimization of the base component of the saturation current. This result is substantiated by an independent analysis of the material used to fabricate these devices

Radiation resistance and comparative performance of ITO/InP and n/p InP homojunction solar cells

The radiation resistance of ITO/InP cells processed by DC magnetron sputtering is compared to that of standard n/p InP and GaAs homojunction cells. After 20 MeV proton irradiations, it is found that the radiation resistance of the present ITO/InP cell is comparable to that of the n/p homojunction InP cell and that both InP cell types have radiation resistance significantly greater than GaAs. The relatively lower radiation resistance, observed at higher fluence, for the InP cell with the deepest junction depth, is attributed to losses in the cells emitter region. Diode parameters obtained from I sub sc - V sub oc plots, data from surface Raman spectroscopy, and determinations of surface conductivity types are used to investigate the configuration of the ITO/InP cells. It is concluded that thesee latter cells are n/p homojunctions, the n-region consisting of a disordered layer at the oxide semiconductor