Improved Efficiency in Hydrogenated Amorphous Silicon Solar Cells Irradiated by Excimer Laser
- PDF / 65,391 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 0 Downloads / 186 Views
L8.2.1
Improved Efficiency in Hydrogenated Amorphous Silicon Solar Cells Irradiated by Excimer Laser A. A. Damitha T. Adikaari, S. Ravi P. Silva, Michael J. Kearney and John M. Shannon Nano-Electronics Centre, Advanced Technology Institute, University of Surrey, Guildford, GU2 7XH, United Kingdom. ABSTRACT Excimer laser crystallisation is used to fabricate nanocrystalline thin film silicon Schottky barrier solar cells, in a superstrate configuration with indium tin oxide as the front contact and chromium as the back contact. 150 nm thick intrinsic absorber layers are used for the solar cells, and was crystallised using an excimer laser with different laser energy densities. These layers were characterised using Raman spectroscopy and optical absorption before device fabrication. External quantum efficiencies of the devices were calculated from the spectral response data of the devices. A maximum efficiency of 70 % is observed for low energy irradiation, which is significant for very thin absorber layers. Device operation is discussed with proposed band structures for the devices and supplementary measurements. INTRODUCTION Excimer laser (EL) crystallisation has been the preferred method for nanocrystalline thin film formation from hydrogenated amorphous silicon (a-Si:H) thin film transistors [1-4]. Pulsed laser energy melts and solidifies thin a-Si:H films within nanosecond time scales, systematically evolving hydrogen and forming nanocrystalline silicon (nc-Si:H). The short wavelength, short pulse duration, ultra violet energy of the excimer lasers is absorbed in the a-Si:H within a few nanometres, with a minimum percentage of heat reaching the substrate. This enables the use of cheap substrates such as glass, which cannot withstand conventional annealing temperatures for large area electronic applications. Although the application has primarily been focused on thin film transistors, its adaptability for photovoltaics has attracted considerable interest over time [57]. Significant emphasis has been placed on investigating layered nanocrystalline silicon formation from partially melting a-Si:H using the excimer laser [8,9]. Partial melting occurs when the laser energy density is low, but sufficient to melt a layer of the film, leaving a continuous solid layer underneath. This process results in a stratified structure with large crystallites from the laser irradiated surface, followed by a fine-grained silicon layer. A third unconverted a-Si:H layer is expected at the bottom, depending on how high the laser energy density used, but its properties may be affected due to conducted heat. In this report, we investigate the utilisation of these very thin, stratified nanocrystalline silicon films as absorber layers in Schottky barrier solar cells. The intrinsic nanocrystalline silicon was characterised using Raman spectroscopy and optical absorption measurements before device fabrication. External quantum efficiency (EQE) of the cells was calculated from spectral response of devices and they will be discussed in detail ex
Data Loading...
