Candidate
Navid Mohammad Sadeghi Jahed
Title
Top-down formation and Surface States studies of ZnO nanowires for PV device application
Supervisor
Siva Sivoththaman
Abstract
The development of scalable techniques for fabrication of nanowire arrays is among the primary goals of third generation photovoltaic (PV) technologies. Application of nanowires in PV devices increases the junction area and provides orthogonality between light absorption and charge collection paths for enhanced power conversion efficiency. Nanowires made from bottom-up techniques are often prone to low geometrical control and random orientation, which limits the performance of the PV device while top-down techniques allows better control over nanowire geometry and orientation. Electron-beam lithography (EBL) is the most studied and widely used top-down method for nanowire fabrication. However, E-beam lithography is expensive and time consuming. We report on top down formation of ZnO NWs combining nanosphere lithography (NSL) and plasma etching which provides a practical, inexpensive and scalable alternative method for fabrication of ZnO nanowires. In order to decrease the surface trap states from the etched ZnO NWs, they were treated with both wet and plasma processes. The effect of these surface treatments were studied through the photoluminescence spectroscopy. Time-resolved spectroscopy was also used to further investigate the transfer dynamics of carriers interface between the treated NW surfaces and quantum dot (QD) films deposited on to the NWs to form the light absorbing layer as a part of PV device. The effect of QD size, ligand types and length on the carrier transfer efficiency will be also presented. This study provides insight and knowledge required for optimizing a QD heterojunction PV device.