Optical and electrical detection and localization of solar cell defects on microscale

Abstract

Monocrystalline silicon wafer is up-to-date most used material for the fabrication of solar cells. The recent investigation shows that the quality of cells is often degraded by structural defects emerging during processing steps. Hence the paper gives first an overview of solar cell efficiency investigation on macroscale. Then a detection and microscale localization of tiny local defects in solar cell structures which evidently affect electrical and photoelectrical properties of the cells is targeted. The local defects can be classified as microfractures, precipitates and other material structure inhomogeneities. Detection and localization of the defects in the structure and the assigning of particular defects to corresponding degradation of photoelectrical parameters are key points for solar cell lifetime and efficiency improvement. Although the breakdown can be evident in current-voltage plot, the localization of defects on the sample has to be provided by microscopic investigations as well as by defects light emission measurement under electrical bias conditions. The experimental results obtained from samples where the defects were microscopically repaired by focused ion beam are presented. Electrical and photoelectrical properties of sample before and after milling processing are also discussed.