The solar photovoltaics industry has shifted from multicrystalline to monocrystalline silicon in manufacturing silicon solar cells over the past few years. Monocrystalline silicon is a single crystal lattice structure with high purity due to relative low concentration of metallic impurities that significantly contribute to the production of high-efficiency commercial silicon cells. However, extrinsic and intrinsic defects are still inevitably present in monocrystalline silicon. These defects are introduced during growth and processing of the crystal and tend to act as potential carrier traps and recombination centers that greatly affect the minority carrier lifetime and efficiency of silicon solar cells. In this thesis, float zone- (FZ) and Czochralski- (Cz) grown silicon cells were used to investigate the electrical characteristics of the defects that act as minority carrier traps or deep level centers in silicon crystals. Electrical techniques were employed which include capacitance-voltage measurements (C-V), deep-level transient spectroscopy (DLTS), high resolution Laplace DLTS, and minority carrier transient spectroscopy (MCTS). The main goals of the thesis are to understand the origin of the defects and to come up with ways to eliminate these defects that significantly impact the performance of silicon cells. This thesis is divided into three research topics: i) Recombination-active thermally-induced defects in float zone- grown silicon; ii) Defects responsible for the light-induced degradation (LID) of solar cells from Czochralski-grown silicon doped with boron; and iii) Minority carrier traps and deep level defects in Cz-grown silicon doped with boron, gallium, aluminium, or indium impurity atoms. The origins of the defects were investigated and some techniques to deactivate the recombination-active defects in FZ- and Cz- grown silicon cells were presented and discussed.
|Date of Award
|1 Aug 2022
- The University of Manchester
|Matthew Halsall (Supervisor) & Iain Crowe (Supervisor)