Pulsed Laser Deposition of Zn(O,Se) Layers for Optoelectronic Application

Zinc oxyselenide—Zn(O,Se)—could become a novel buffer layer in solar cells and a functional layer in different optoelectronic devices. In this study, we systematically investigated the influence of the deposition temperature ranging from room temperature (RT) to 650 °C on the structural and optoelectronic properties of Zn(O,Se) layers grown on photovoltaic (PV) glass substrates by one-step pulsed laser deposition in a high vacuum. All layers were characterized using energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), X-ray diffractometry (XRD), UV–vis spectroscopy, and the Hall and van der Pauw technique. We demonstrated that polycrystalline, uniform, and electrically conductive Zn(O,Se) layers were grown at the substrate temperatures of 500–650 °C, while those layers grown at temperatures below 500 °C were characterized as amorphous and exhibiting a semi-insulating behavior. According to the XRD data, single-phase layers consisting of a ternary Zn(O,Se) phase were formed only at 500 °C. The lattice parameters monotonously decreased with both increasing deposition temperature and lowering Se concentrations in the films. The electron density increased significantly from 1.0 × 1014 to 3.2 × 1018 when changing the substrate temperature from 500 to 550 °C. We attributed these changes to the formation of vacancy-type defects in the Zn(O,Se) system. For the first time, we demonstrated the applicability of Zn(O,Se) as a buffer layer in a complete solar cell structure. We developed a prospective superstrate configuration FTO/Zn(O,Se)/CdTe/Te/Ni solar cell exhibiting a cell efficiency of 7.6% (FTO, fluorine-doped tin oxide). Our findings revealed the great potential of Zn(O,Se) to replace conventional CdS buffer layers and to open up new strategies to improve solar cell performance.