Doping Sensitive Optical Scattering In Zinc Oxide Nanostructured films For Solar Cells

Abstract

The nanostructured ZnO thin films are used in solar cells as heterojunction window layer as well as to enhance the junction area. Nanostructures also offer advantage of light scattering property to transmit more light into the absorber layer of solar cells. The optical and light scattering property of the nanostructured ZnO thin films doped with Al and Cu have been studied. The homogeneously doped ZnO nanostructured films were synthesized by a flux sublimation technique at ~ 300°C temperature. The structural studies show hexagonal nanocrystal growth in Al doped ZnO film and nanowire structure in Cu doped ZnO film. These doped ZnO films consistently showed two direct band gaps. The low energy band gap of Al and Cu- doped ZnO films originates from the macroscopic structural feature in the film, and the higher energy band gap due to the quantum confinement of nanostructure clusters in the film. Increased transmission in the lower wavelength region is caused by the forward light scattering by the nanostructure. Simulation of the optical absorption spectra of the Al and Cu- doped ZnO films using the modified Mie scattering theory shows consistent match with the experimental absorption spectra. The results show that increased forward scattering of light could be harvested by increasing the nanoparticle density which will enhance the photocurrent generation from the thin film solar cells by using doped ZnO nanostructured film as a window layer or as a transparent conducting electrode. Copyright © 2013 VBRI press.