RF-sputtered Al-doped ZnO thin films: Optoelectrical properties and application in photovoltaic devices

Abstract

An attempt has been made to prepare Al-doped ZnO thin films by rf sputtering at different argon pressures and low substrate temperatures of 80–95 °C to ascertain the conditions rendering optical and electrical characteristics useful for their applications in photovoltaic devices. The increase in argon pressure is shown to influence their morphology, optical absorption, photoluminescence spectrum, and electrical behavior. The increase in resistivity is attributed to reduced carrier mobility. The variation in energy bandgap has been explained by invoking Burstein–Moss widening and bandgap narrowing effects arising due to increase in the carrier concentration. AZO films obtained at argon pressure of 0.15 Pa exhibit (i) wurtzite-type hexagonal structure with [0001] preferred orientation, (ii) high optical transmittance of ∼85% in the wavelength range 400–800 nm, and (iii) low electrical resistivity of 9.54 × 10−4 Ω cm and hence can be potential alternative transparent conducting oxides. Moreover, the performance of the organic solar cells and light-emitting diodes fabricated with AZO films as anode has been demonstrated.