Effects of sputtering conditions on the photovoltaic properties of Al-doped zinc oxide films for Cu(In,Ga)Se2 thin-film solar cells

Abstract

This study aimed to elucidate the effects of sputtering conditions on the optical and electrical properties of AZO films prepared via a RF-magnetron sputtering. A rise in the substrate temperatures promoted the grain growth and reduced the grain boundaries of AZO films, thereby resulting in reduced resistivity. As the substrate temperature was raised to 150 °C, the crystallinity of the prepared films was improved and AZO films having high conductivity were obtained. With further supply of oxygen as the sputtering gas during deposition, the average transmittance of AZO films in NIR region was gradually increased from 86.2 to 91.4% due to reduced free carrier absorption. The improvement in the optical transmittance leads to an increase in the short-circuit current of the fabricated Cu(In,Ga)Se2 solar cells. Hence, the conversion efficiency of solar cells fabricated by using the obtained AZO films was enhanced from 11.2 to 11.7% when the oxygen concentration was increased from 0 to 0.5%. As the oxygen concentration was further increased to 10 vol%, the obtained AZO films exhibited elevated resistivity and low carrier mobility which deteriorated the photovoltaic properties of the solar devices. This investigation revealed that the photovoltaic performance of Cu(In,Ga)Se2 solar cells was improved via adjusting the oxygen concentration in the sputtering gas.