Wide-Bandgap CIAS Photovoltaic Absorber on Flexible Substrates

Thin-film photovoltaic cells offer the promise of high specific power arrays for space applications. Two thin-film photovoltaics technologies are presently vying for use in space applications; copper-indium-gallium-diselenide (CIGS), and amorphous silicon. This proposal focuses on efficiency improvements to the CIS-alloy technologies by the continued development of a third possibility, copper-indium-aluminum-diselenide (CIAS). This wide-bandgap thin-film technology will be deposited by co-evaporation at low substrate temperatures on sub-bandgap light transparent back contacts and lightweight, flexible and sub-bandgap light transparent polyimide substrates. To achieve the optimum bandgap of about 1.45 eV for the space solar spectrum, less than half the amount of aluminum (Al) is needed in CIAS, then gallium (Ga) in CIGS. Thus, using Al may avoid a concentration limit (bandgap limit) similar to the amount of Ga in CIGS for the degradation of material electrical quality due to Ga-Ga defect complexes. Other advantages of the proposed technology include: higher-efficiency modules due to lower resistive and distributed diode losses; higher-efficiency modules at higher operating temperatures due to more favorable temperature coefficients of cell parameters and complete IR transmission; potential for backside array visible light collection, and high end-of-life-efficiency modules due to inherent charged particle radiation resistance of CIS based alloys.