Abstract
CuInSe2 absorber layer prepared by electrodeposited Cu-In metal precursor followed by selenization has been successfully fabricated and the device with 9.3% efficiency on 0.12 cm2 were demonstrated. First, single layer Mo films with different thickness are sputtered on glass and found the sheet resistance and reflectance of visible light approach to a constant value when thickness greater than 100 nm. Sputtered Mo films were under tensile stress (5~7 GPa) and easy exfoliation, thus we conclude a better Mo structure with bilayer and 0.5μm thickness followed the NREL and others results. After electrodepositing Cu-In metal films, the samples were put into tube furnace with Se pieces for selenization. By XAS analysis that In is easilier to react with Se than that of Cu to form binary selenides. During the selenization at 300~350℃ films tend to form bilayer structure with CuSex on top and InSex near the Mo back contact. The film transformed to CuInSe2 uniformly after selenization at 450~500℃. The other issue is MoSe2 formation during selenization, it improves the adhesion at CIS/Mo interface if a moderate thickness (100~200 nm) was formed but it also increases the series resistance of solar cell for a thick MoSe2 (almost Mo were selenized ). We propose a two steps selenization process for supplying overdose Se at first then reducing Se at final step to control MoSe2 thickness below 500 nm without affecting CuInSe2 grain growth.