I am fabricating thinfilm solar cells on metallic copper foils using chemical spray pyrolysis technique. The idea is that by spraying Indium Sulfide(INS) over Copper foils placed on a heater ; copper from the foil will diffuse to the INS layer to form copper indium sulfide( p-type) and hence forming a p-n junction with the INS( n-type ) whatsoever left undiffused. From XRD, I could ensure the formation of CIS. J-V characterization of the device shows good diode characteristics (Please find the attached J-V curve) but on illumination the device doesn’t yield any photovoltaic response. Whatever variations I do, I always get almost the same characteristic curve but no change in J or V on illumination. So is there something of prime importance that I need to check ? How can I check that the junction that I obtained is a p-n junction indeed or a schottky junction? And most importantly what would be the reason that I’m not getting any photovoltaic response though I’m getting good dark characteristics?