The n-Cu_0.9Ag_0.1In₃Se₅chalcopyrite, 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.

Diffusion coefficients of two mobile ions in three AB3In7VI12 single crystals (AB=Cu and Ag VI=Se or Te). Proposition of an equivalent electrical circuit

“…In order to measure the slice resistivity, graphite paint is utilized as electrodes in both the sample faces due to have a good ohmic contact [6,7]. Electrical properties are analyzed from the electrical circuit in DC polarization using a non-destructive method based in the current or potential decay method that studying changes of potential, V m , or current intensity, I, or sample resistance, R m , within time in a point contact under a fixed external potential.…”

“…Other three broad peaks are assigned to Cu-Se and In-Te vibrations and indicate high disorder attributed entirely to the Cu and In sublattice [5]. In CuIn 3 Te 5 and Cu 0.9 Ag 0.1 In 3 Se 5 single crystals, the electrical resistance varies within time due to current intensity variation that is analyzed in terms of the hypothesis of an ionic motion [6,7]. A single defect (vacancy or interstitial) can be responsible for ion motion, depending on the compound structure [8].…”