Regular Article

Copper:molybdenum sub-oxide blend as transparent conductive electrode (TCE) indium free^*

¹ LOPCM, Université Ibn Tofail, Faculté des Sciences, BP 133, 14000 Kenitra, Morocco
² Université de Nantes, Institut des Matériaux Jean Rouxel (IMN), CNRS, UMR 6502, 2 rue de la Houssinière, BP 92208, 44000 Nantes, France
³ Université de Nantes, Dpt Physique, 2 rue de la Houssinière, BP 92208, 44000 Nantes, France
⁴ Université de Nantes, MOLTECH-Anjou, CNRS, UMR 6200, 2 rue de la Houssinière, BP 92208, 44000 Nantes, France

^a e-mail: hss.mehdi@gmail.com

Received: 3 July 2015
Revised: 23 September 2015
Accepted: 2 October 2015
Published online: 3 May 2016

Abstract

Oxide/metal/oxide structures have been shown to be promising alternatives to ITO. In such structures, in order to decrease the high light reflection of the metal film it is embedded between two metal oxides dielectric. MoO_3-x is often used as oxide due to its capacity to be a performing anode buffer layer in organic solar cells, while silver is the metal the most often used [1]. Some attempts to use cheaper metal such as copper have been done. However it was shown that Cu diffuses strongly into MoO_3-x [2]. Here we used this property to grow simple new transparent conductive oxide (TCE), i.e., Cu: MoO_3-x blend. After the deposition of a thin Cu layer, a film of MoO_3-x is deposited by sublimation. An XPS study shows more than 50% of Cu is present at the surface of the structure. In order to limit the Cu diffusion an ultra-thin Al layer is deposited onto MoO_3-x. Then, in order to obtain a good hole collecting contact with the electron donor of the organic solar cells, a second MoO_3-x layer is deposited. After optimization of the thickness of the different layers, the optimum structure is as follow:

      Cu (12 nm) : MoO_3-x (20 nm)/Al (0.5 nm)/ MoO_3-x (10 nm).

The sheet resistance of this structure is R_sq = 5.2 Ω/sq. and its transmittance is T_max = 65%. The factor of merit ϕ_M = T¹⁰/R_sq. = 2.41 × 10^-3 Ω^-1, which made this new TCE promising as anode in organic solar cells.