PRELIMINARY INVESTIGATION ON TRIPLE JUNCTION InGaP/InGaAs/Ge SOLAR CELLS GROWN ON THIN WAFERS FOR SPACE AND TERRESTRIAL APPLICATION

摘要

Development of triple junction solar cells (TJ) on thin germanium substrates is desirable both for space and terrestrial application. In the former case launch cost can potentially be reduced, while in the second case thermal management in concentrator solar cells is facilitated. The use on thin Ge substrates (100 μm or less) represents however a challenge for solar cell growth and device manufacturing, owing to the reduction of the substrate mechanical strength. We have exploited the recent availability of in-situ MOCVD monitoring tools to look at the stress evolution during the growth of the solar cell structure. A Veeco in-situ single beam deflectometer has been installed on a production E450LDM reactor and for the fist time, the curvature and reflectivity behaviour of InGaP/InGaAs/Ge triple junction solar cell structures have been monitored and analysed during the entire growth cycle. TJ solar cells grown on thin wafers with 25.4% AM0 efficiency and 30% out-door 42 sun efficiency values have been obtained combining the optimisation of the solar cell structures suggested by in-situ monitoring of the wafer curvature with the proper modification of the manufacturing process.