High-efficiency GaInP/GaAs tandem solar cells

GaInP/GaAs tandem solar cells have achieved new record efficiencies, specifically 25.7% under air-mass 0 (AMO) illumination, 29.5% under AM 1.5 global (AM1.5G) illumination, and 30.2% at 140-180x concentration under AM 1.5 direct (AM1.5D) illumination. These values are the highest two-terminal efficiencies achieved by any solar cell under these illumination conditions. The monolithic, series-connected design of the tandem cells allows them to be substituted for silicon or gallium arsenide cells in photovoltaic panel systems with minimal design changes. The advantages of using GaInP/GaAs tandem solar cells in space and terrestrial applications are discussed primarily in terms of the reduction in balance-of-system costs that accrues when using a higher efficiency cell. The new efficiency values represent a significant improvement over previous efficiencies for this materials system, and we identify grid design, back interface passivation, and top interface passivation as the three key factors leading to this improvement. In producing the high-efficiency cells, we have addressed nondestructive diagnostics and materials growth reproducibility as well as peak cell performance     

The CLFM: A Method of Generating Linear Frequency-Coded Radar Pulses

A simple method of generating a coherent linear frequency-modulated pulse, suitable for use in a radar pulse-compression system, is described. The method, termed CLFM, employs a swept-frequency oscillator with closed-loop control of its phase. The phase-error voltages for the loop are obtained by sampling the waveform at regular intervals. The sampling technique itself is unconventional and avoids the need for large bandwidth circuitry. Results obtained with a demonstration model of the CLFM, generating a signal with a time-bandwidth product of 1000, are described.     

CAVORT: A Radar Pulse Train Optimum Processor for Accelerating Targets

The CAVORT analog radar signal processor for matched filtering of coherent pulse trains from targets displaying significant radial acceleration is described. CAVORT employs a scanning technique to search repeatedly through trial pairs of values for Doppler and Doppler rate. When a target appears, it is detected, and the best-fitting pair of values determined. The principle of operation is illustrated, using photographs of waveforms generated by the equipment. The resuilts of satellite observations are included. It is demonstrated that the experimental CAVORT which integrates half-second segments of signal gives satisfactory estimates of acceleration.