Synthesis of conducting Zn 1 − xMg xO: Al layers by spray pyrolysis for photovoltaic application

Abstract

In recent years, Zn 1 − x Mg x O has attracted the attention of many researchers as its physical behavior can be suitably controlled by varying the Zn/Mg ratio. Also, it has high stability with low toxicity and the abundance of constituent elements. Further, the band offsets can be tuned to a minimum level with respect to a heterojunction partner by suitably controlling the Zn/Mg ratio. These properties make this material as a potential candidate as a buffer layer in the fabrication of Cu(In,Ga)Se 2-based solar cells. In our previous study, Zn 1 − x Mg x O films prepared by spray pyrolysis at 300 °C have shown high resistance and optical transmittance with wide energy band gap. However, it is interesting to note that if the films were conducting, then they can also be used as window layers. In the present investigation, Zn 0.76Mg 0.24O films have been prepared by spray pyrolysis at an optimized substrate temperature of 300 °C with different dopant concentrations that vary in the range, 0–6%. X-ray diffraction analysis showed that the films were polycrystalline and exhibited wurtzite crystal structure with a preferential c-axis orientation. The influence of Al doping on the electrical resistivity was found to be significant. The average transmittance of the films was found to be > 60% in the visible range with a small variation in the optical energy band gap. The changes occurred in the structure, topography, composition, electrical and optical properties of the layers as a function of dopant concentration have been studied.