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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. It is shown that the normalized values of the unit cell parameters a and c of the ordered defect compounds with respect to their corresponding 1:1:2 phase, that are formed on the In(Ga)-rich side of the pseudo-binary phase diagram of [Cu2(Se,Te)]X–[(In2,Ga2)(Se3,Te3)]1-X, vary linearly with the effective cation radius reff for the tellurides and selenides of Cu-In and Cu-Ga systems. This universal relationship has important significance. The unit cell dimensions of other chalcopyriterelated ordered defect compounds of these systems that have not been synthesized so far can be estimated. 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.