Magnetotransport Properties of Copper Ternaries: New Solar Cells Materials

Abstract

Ever since the first solar cell was developed by Bell Laboratories, new materials are being investigated that could yield solar energy conversion efficiency comparable in device production cost to the standard electric power generators. Continuing with this effort, in recent years solar cells with efficiency close to 20% prepared with alloys of CuIn1-xGaxSe2 has been reported. On the other hand, it is, suggested that n-CuIn3Se5 combined with p-CuInSe2 could play an important role in the optimization of solar cells based on Cu-ternaries. In addition to their technological importance, these compounds are also of academic interest. Because of the presence of shallow donor and acceptor levels due to the presence of cation-cation disorders in Cu(In,Ga)Se2 and ordered defects in Cu(In,Ga)3 (Se,Te)5, the impurity band in these compounds starts to form between liquid helium and nitrogen temperatures. This permits to study the variable range hopping (VRH) conduction in the impurity band over a much wider temperature range. In the case of Mott type VRH, the electrical resistivity follows the relation ρ = ρexp (T /T)1/4, where ρ pis the pre-exponential factor and Tρ is the characteristic temperature. In this paper we report on a comparative study of the variation of electrical resistivity over a wide temperature range at different magnetic field values in single crystals of CuInSe2, CuInTe2, CuGaTe2, CuIn3Se5, CuIn3Te5 and CuGa3Te5. Results related to the variable range hopping and metallic conduc-tion mechanisms are discussed. The magnetoresistance data of n–CuInSe2 in the variable range and p–CuGaTe2 in the metallic regimes, measured in pulsed magnetic field up to 25 T between 2 and 300 K are analyzed and compared with the existing theoretical models.