Annealing induced AgInSe2 formation from Ag/In/Ag/In multilayer film for solar cell absorbing layer

In the present study, the AgInSe2 (AIS) thin films 500 nm in thickness were prepared by selenization of the Ag/In/Ag/In multilayer deposited by DC magnetron sputtering. The selenization was carried out at 250 °C and was followed by annealing at 450 °C, 475 °C and 500 °C. The selenized and annealed films were characterized by grazing incidence X-ray diffraction (GIXRD), UV-Visible-NIR spectroscopy, Field-Emission Scanning Electron Microscopy (FESEM) and Raman spectroscopy. The XRD analysis revealed the formation of the desired AgInSe2 phase along with Ag2Se (AS) impurity phase. The impurity Ag2Se phase is being diminished at higher annealing temperature (500 °C) resulting the formation of AgInSe2 phase. The super ionic nature of α-Ag2Se phase facilities the diffusion of Ag ion with its neighbouring tetrahedral sites. The low band gap Ag2Se impurity phase suppression by annealing at 500 °C lead to optical band gap increase. The Raman spectrum shows individual AgInSe2 and Ag2Se peaks and also the overlapping of these two phases. The Ag2Se peaks are vanished after annealing. The EDXRF study revealed that the film is off-stoichiometric and exhibit n-type conductivity. The RBS analysis indicates the diffusion of the film material to the glass substrate. From Hall measurement it is confirmed that the film shows n-type conductivity and the resistivity decreases with increasing the annealing temperature.