Role of Pre-Layer Mo Films in Microstructural and Morphological Properties of Over-Layer CIGS Films
- PDF / 996,746 Bytes
- 10 Pages / 612 x 792 pts (letter) Page_size
- 116 Downloads / 181 Views
Role of Pre-Layer Mo Films in Microstructural and Morphological Properties of Over-Layer CIGS Films Hamda A. Al-Thani1 and Falah S. Hasoon1 1 National Energy and Water Research Center (NEWRC), POBOX 54111, Abu Dhabi, UAE ABSTRACT This study focuses on establishing a microstructural and morphological correlation between CIGS films and its precursor layer of Molybdenum (Mo) coated soda-lime glass (SLG). Therefore, variations in the morphology and microstructural properties of Mo thin films, using DC planar magnetron sputtering, were induced systematically by varying the sputtering pressure from 0.6 to 16 mT with a sputtering power density of 1.2 W/cm2. Subsequently, under fixed deposition conditions (deposition rate and substrate temperature), a growth of Cu(In,Ga)Se2 (CIGS) films was carried out on the Mo-coated SLG substrates, using the 3-stage growth process of the physical vapor deposition (PVD) technique. High-Resolution Scanning Electron Microscopy (HRSEM) was used to examine the Mo and CIGS films morphology. X-Ray Diffraction (XRD) was applied to study in detail the microstructure of Mo and CIGS films. Where, the films’ crystal structure including the preferred orientation and the lattice parameters were determined by the /2 XRD technique and by applying Cohen’s least-square method. Furthermore, Atomic Force Microscopy (AFM) was used to determine the root-mean-square (RMS) surface roughness of the CIGS films. INTRODUCTION Molybdenum (Mo) is one of the most important materials used as a back contact for thin film solar cells. This interest in using Mo thin films arises from its high thermal stability (high melting temperature), mechanical strength, and its electronic properties (low resistivity) [1, 2]. Sputter deposition is the common deposition process for Mo thin film [3]. Significant changes in the properties of the growing Mo films may be induced by varying the working gas pressure during the sputtering process. The films experience lattice expansion and thus compressive stress with dense microstructure at relatively low sputtering pressure due to the high kinetic energy of the arriving atoms. When less energy is provided to the film at relatively high sputtering pressures, films exhibit tensile stress with open porous microstructure [4-6]. The current highest CIGS, CIS, and CGS based solar cells’ efficiency has been achieved by physical vapor deposition technique from elemental sources using three stage (3-stage) process [7, 8], deposited on Molybdenum coated soda lime glass (Mo/SLG). The efficiency of laboratory scale solar cells is now near 21% and that of commercial modules is around 17.5% [9]. At CIGS thin film processing temperature of ~ 580C, Na content in the SLG exhibits a low diffusivity in the Mo lattice through its grain boundaries, whereas for the temperature range of 800 1000C the diffusivity of Na becomes quite high (~ 10-10 cm2/s) [10]. Hence, the microstructure properties of Mo films, which depend on the sputtering conditions, affect strongly the out-diffusion of Na and its incorporat
Data Loading...
