Investigation of valence electron excitation and plasmonic enhancement in sputter grown NMZO thin films: For energy harvesting applications

Abstract

We report a novel approach of sputter-stimulated plasmonic generation in Na-doped MgZnO (NMZO) thin films. Sputtering of material during film growth by utilizing secondary direct-coupled ion-source present in dual-ion beam sputtering system leads to the generation of nanoclusters of its constituent elements due to different sputtering-out rates of various elements present in the films. The authentication of plasmonic generation in NMZO is conducted as follows a) identification of plasmonic signature in electron energy loss spectra obtained by ultraviolet photoelectron spectroscopy measurement, b) valence bulk, valence surface, and particle plasmon resonance energy calculations are performed, and each plasmon peak is indexed with corresponding plasmon energy peak of different nanoclusters, and c) spectroscopic ellipsometric measurement is deployed to verify plasmonic behavior by investigating different optical properties. Additionally, incorporation of the plasmonic feature along with alkali metals plays a crucial role in the improvement of the performance of solar cells. Therefore, plasmon enhanced NMZO as a backscattering layer in between CIGSe/back contact is probed to ascertain the additional benefits of 1) Na incorporation into the absorber layer as a result of the Na diffusion from the NMZO layer, and 2) improvement in the morphology of the CIGSe thin film with the incorporation of NMZO layer in between the back-contact and CIGSe. The diffusion of Na into the absorber layer is probed by deploying secondary ion mass spectroscopy measurements, and improvement in the morphology of CIGSe with the incorporation of NMZO layer between the back-contact/absorber is investigated using field-emission scanning electron microscope analysis. © 2018 Elsevier B.V.