The n-Cu0.9Ag0.1In3Se5 chalcopyrite, electronic as well as ionic conductor

Abstract

A resistance increase with time of the n-Cu0.9Ag0.1In3Se5 chalcopyrite has been observed. This new effect is analysed in terms of a hypothesis of ion migration and Schottky barrier formation. These results might explain why different solar cell efficiencies are obtained for the chalcopyrites, CuInSe2 and CuIn x Ga1−x Se2, when an In-rich film is deposited on top of the chalcopyrite. In these solar cells, ion migration can exist and a new effect appears similar to the one observed in our compound. The ions, probably the cations, are moved by the electrical field towards the cathode. A gradient of mobile ions appears across the sample and the positive charge is accumulated near this electrode such that it varies the metal–semiconductor interface. This interface is a Schottky barrier where the contact potential is a function of time due to the arrival of ions. The electrical measurements have been carried out on a solid state device, graphite/n-Cu0.9Ag0.1In3Se5/graphite. The current intensity and the potential drop across the sample have been measured with time when a constant electrical potential is applied for 600 s at dark or under ultraviolet illumination and at room temperature. A comparative study in similar electrical conditions is done; the current intensity difference and the potential drop across the difference (under ultraviolet illumination minus at dark) are not constant and both measurements increase with time.