Novel techniques for evaluation of interconnections in solar cells used for spacecraft power generation

Solar cells used to power satellites are subject to diurnal temperature extremes more severe than those found on Earth. The resulting expansion and contraction can cause failure of interconnection welds because of differences among expansion coefficients. An experimental investigation of the reliability effects of thermal cycling on interconnections for one type of solar cell was conducted. The solar cells evaluated are single junction GaAs photovoltaic structures on germanium substrates. Welds are made between silver metallization on the solar cell and a silver plated molybdenum interconnect. Three experimental techniques were used for weld assessment: infrared imaging to identify locations where resistance to current causes Joule heating; cross sectioning of sample solar cells; and ultrasonic imaging. The experimental results are described, and conclusions of how the methods compare in accuracy and ease of use are given.