Diffusion of Cu, In, and Ga in In2Se3/CuGaSe2/SnO2 thin film photovoltaic structures

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Abstract
This article is a study of copper,indium, and galliuminterdiffusions in In 2 Se 3 / CuGaSe 2 / SnO 2 / glass thin filmheterostructuresannealed at different temperatures. The use of CuGaSe 2 material in place of Cu(In,Ga)Se 2 is only required by the indiumdiffusion studies. The CuGaSe 2 layers were grown by close-spaced vapor transport for two types of sources having different grain sizes. The In 2 Se 3 films were deposited by thermal evaporation. The heterostructures were annealed in vacuum at different temperatures and analyzed by secondary ion mass spectroscopy(SIMS). The copper,indium, and galliumSIMS concentration profiles show that the copper diffuses up to the In 2 Se 3 film surface and that the indium can diffuse far away from the In 2 Se 3 / CuGaSe 2 interface towards SnO 2 . The copper,indium, and galliumdiffusions were studied and the interdiffusion parameters were computed. The simultaneous interdiffusions of copper and indium induces the formation of a p–n junction responsible for the photovoltaic effect of the Zn/In 2 Se 3 / CuGaSe 2 / SnO 2 / glass photocells, the SnO 2 side being lighted. This hypothesis is supported by results carried out from electron beam induced current measurements, showing a notable shift of the junction from the In 2 Se 3 / CuGaSe 2 interface through the CuGaSe 2 layer in terms of the annealing temperature, resulting in an increasing of the photovoltages up to 650 mV.