Evolution in morphological, optical, and electronic properties of ZnO:Al thin films undergoing a laser annealing and etching process

Abstract

The use of a combined excimer (XeCl=308nm) laser annealing (ELA) and chemical etching process (dubbed the “LaText” process) to generate textured ZnO:Al thin films suitable for thin-film silicon photovoltaic applications has been previously shown, but the evolution of the material during the laser annealing and texturing steps has not been thoroughly examined. In this work, we examine in detail the evolution of the properties of room-temperature sputtered ZnO:Al thin films during such a process. We reveal (i) the bulk structural changes induced during laser annealing through X-ray diffraction measurements (XRD) and Raman spectroscopy, (ii) the dramatic changes in surface morphology and macroscopic electronic properties before and after each step of the LaText process, through Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Hall effect measurements, and (iii) the exceptional light scattering properties of these films in both air and in a cell configuration, as measured by optical transmission and reflection measurements. In all, we show that the electronic transport properties in the final state are acceptable for thin film PV applications, and the optical properties are exceptional and demonstrate great potential for light-trapping performance for both a-Si:H and µc-Si:H solar cells.