Development of High Efficiency Cu2ZnSnS4 Solar cells by Contacts and Interface Engineering

Abstract

Pure sulphide Cu2ZnSnS4 is a promising photovoltaic absorber material. It consists of earth-abundant and environmentally-friendly constituents, and has an optimal bandgap for single junction high efficiency solar cells. In this thesis, contacts and interface of Cu2ZnSnS4 device are engineered and systematically studied toward high efficiency. Chapter 3.1 present the hybrid silver nanowire network/ultra thin ITO as the transparent conductive electrode for Cu2ZnSnS4 solar cells, replacing the scarce and expensive ITO. In chapter 3.2, for the new hybrid transparent electrode, sputtered intrinsic zinc oxide is introduced as an anti-reflective coating replacing MgF2 in traditional Cu2ZnSnS4 solar cells. Chapter 3.3 introduces mechanical transfer method for pre-annealed silver nanowire on Cu2ZnSnS4 devices in order to achieve more conductive transparent conductive electrode. Chapter 4 reports a new route of surface and grain boundary passivation by introducing hydrogen from the atomic layer deposited-Al2O3 layer into Cu2ZnSnS4 solar cells. Different amount of hydrogen is incorporated into Cu2ZnSnS4 / CdS interface and their devices performance is compared. In Chapter 5.1, thermal evaporated MoO3 layer as a primary back contact is introduced. The effects of incorporating MoO3 in back contact are investigated. The MoO3 layer enhances sodium diffusion into Cu2ZnSnS4 absorber, facilitating the formation of larger grains during sulfurization. Chapter 5.2 presents atomic layer deposited-Al2O3 as a blocking layer. Al2O3 layer is deposited on Mo and its function to prevent sulfur diffusion to Mo substrate is discussed.