AgGaSe2 material is a chalcopyrite semiconductor and has a high absorption coefficient because of direct band gap structure.
AgGaSe2 material is well known as a nonlinear optical semiconductor but it is hardly studied as solar cell device. An efficiency of energy conversion of more than 8% has been reported recently on Ag(InGa)Se2 [1]. Therefore, we study AgGaSe2 material to prepare a tandem solar cell of Ag(InGa)Se2.
AgGaSe2 thin film was deposited on glass substrates by vacuum evaporation method. The starting material was mixed Ag2Se and Ga2Se3 powders. Ag/Ga rates were between 0.7 and 1.5. The samples were annealed from 100 to 600 °C for 10 min. This method is very low cost and easier than any other methods. After these processes, crystallographic properties of AgGaSe2 thin films were investigated using X-ray diffraction (XRD). Optical properties by using transmittance and reflectance.
XRD spectra showed Ag, Ag2Se, Ga2Se3 peaks below annealing temperature at 300 °C. AgGaSe2 phase started to grow at 400 °C. Single phase AgGaSe2 could be grown at 600 °C. It was considered that AgGaSe2 single phase could be grown by thermal energy. By using optical transmittance and reflectance measurements, a high absorption coefficient more than 104 cm-1 could be obtained. Furthermore, a bandgap energy could be estimated to be 1.782 eV.
[1] K. Yamada, N. Hoshino and T. Nakada: Ex. Abstract, PVSEC-14 (2004), p.118.
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