Nanoscale electrical characterization by advanced conductive atomic force microscopy techniques of all oxide heterojunctions

Abstract

This thesis investigates the nano - electrical properties of a metal oxide semiconductor for photovoltaic applications. Three p-Cu2O/n-TiO2 and one TiO2 (bare) samples were investigated during the thesis. The main difference between the three p-Cu2O/n-TiO2 nanowires samples is the thickness of the absorber layer, the cuprous oxide. Amplitude Modulation Kelvin Probe Force Microscopy (AM-KPFM) and Intermodulation Electrostatic Force microscopy (ImEFM) have been employed to map nanoscale surface potential of Cu2O/TiO2 and TiO2 (bare) under ambient condition and under nitrogen atmosphere. The four samples were tested in dark, light condition and the best results were obtained in the case of ALD208 where the thickness of the absorber layer it was the smallest among the set of the samples. The conductive atomic force microscopy it was employed to obtain the current distribution on the surface of the sample and the best result were obtained in the case of ALD208. The scanning electron microscopy showed a sample with a uniform topography where the average diameter of the nanowires was 84 nm in the case of TiO2 (bare) and 118 nm in the case of Cu2O/TiO2. The Micro Raman spectroscopy confirmed the presence of the dominant peaks of titania (as rutile) at 240, 430 and 630 cm-1 and the presence of cuprous oxide 218 and 148 cm-1. The results demonstrate that the use of p-Cu2O/n-TiO2 could make possible to construct a high performance solar cell, which could revolutionise the field of clean energy.