CIGS2 thin-film solar cells on flexible foils for space power

Abstract

CuIn1-xGaxS2 (CIGS2) thin-film solar cells on flexible stainless steel foil are of interest for space power because of the near optimum bandgap, potential for higher specific power, and superior radiation resistance. This paper describes development of CIGS2 solar cells on 127-μm and 20-μm-thick, flexible SS foils for space power. A large-area, dual-chamber, deposition system has been fabricated. Cu-rich Cu-Ga/In layers were sputter-deposited on unheated Mo-coated foils. p-type CIGS2 thin films were obtained by etching Cu-rich surface layer from CIGS2 films prepared by sulfurization in Ar:H2S 1:0.04 mixture at 475°C for 60 min with an intermediate 30-min annealing step at 135°C. Solar cells were completed by deposition of CdS/ZnO/ZnO:Al layers and Ni/Al contact fingers. AM0 PV parameters of a CIGS2 solar cell on 127-μm-thick SS foil measured at NASA-GRC were: VOC = 802.9 mV, JSC = 25.07 mA/cm2, FF = 60.06%, and efficiency = 8.84%. For this cell, AM1.5 PV parameters measured at NREL were VOC = 763 mV, JSC = 20.6 mA/cm2, FF = 67.4%, and efficiency = 10.4%.