Highly stable Al-doped ZnO transparent conductors using an oxidized ultrathin metal capping layer at its percolation thickness

Abstract

Metal capping layer can be used to enhance the physical properties of thin films. We propose a transparent conductor structure made of Al-doped ZnO (AZO) and an oxidized Ni capping layer, the latter with a thickness in proximity of its percolation threshold (2.5 nm). The capping layer inhibits the penetration of oxygen and water into the AZO’s grain boundaries thus significantly increasing the stability of the combined structure, as it is shown by its resistance in damp heat testing at 95 °C and 95% humidity. In addition, the oxidized Ni capping layer increases the performance of AZO transparent anodes in organic light emitting diodes by producing efficiencies as high as those of indium-tin-oxide based devices.

On the environmental stability of ZnO thin films by spatial atomic layer deposition

“…31,32 The stability of the electrical and optical properties of ZnO can be enhanced when preventing a direct exposure of the film to atmosphere by using a moisture diffusion barrier. 33,34 The Al 2 O 3 is known to be an excellent gas diffusion barrier, capable of achieving intrinsic water vapor transmission rates (WVTR) in order of 10 À5 g/m 2 /day when grown by conventional ALD. [35][36][37] A similar value of intrinsic WVTR (10 À5 g/m 2 /day) has been measured for spatial-ALD Al 2 O 3 thin-films grown at $0.2 nm/s and a temperature of C, 85% RH environment.…”

Environmental stability of high-mobility indium-oxide based transparent electrodes

“…In fact, capping of DH-sensitive TCOs to improve their stability to heat and humidity is a known effective approach, as demonstrated earlier for ZnO electrodes. 16,34,35 In summary, we have studied the sensitivity to heat and humidity of sputtered ITO, IO:H, IZO, and IO:H/ITO bilayers front contacts used in solar cells by DH test. We found that polycrystalline ITO and amorphous IZO films feature high stability to heat and humidity, thus promising long term stability, needed for large-scale deployment of solar cells, whereas polycrystalline IO:H films degrade under DH exposure.…”

Influence of atmosphere and material properties on damp heat stability of ZnO:Al

“…The stability of ZnO:Al can be improved by introduction of barrier layers . In previous work, we have demonstrated damp heat stable ZnO:Al films after annealing under a protective silicon layer, which had been removed before degradation .…”