C.P. Lund

Renewable energy education for sustainable development

Rising international concern about global warming and the rapid development of the renewable energy industry over recent years has led to a need for multidisciplinary programs in energy studies. We have developed a postgraduate program in energy studies which is based on the principles of ecologically sustainable development. This program combines work in energy technology with energy policy, energy economics and environmental and social issues. The program is offered on campus at Murdoch University and by external study, via the internet, throughout Australia and overseas. It has attracted considerable interest from students seeking to find new opportunities within the renewable energy industry. This paper outlines the philosophy of the energy studies program, its implementation and outcomes.

Field and laboratory studies of the stability of amorphous silicon solar cells and modules

If photovoltaic solar cells and modules are to be used as a major source of power generation it is important to have a good knowledge and understanding of their long-term performance under different climatic and operating conditions. A number of studies of the long-term performance of commercially available photovoltaic modules manufactured using different technologies have now been reported in the literature. These have shown clear differences in the seasonal and long term performance and stability of different solar cell techniques. In addition to general module engineering factors that result in a loss of performance in all modules some types of solar cells, such as those made from thin film amorphous silicon (a-Si:H), also suffer specific losses in performance due to fundamental material changes, such as photodegradation or the Staebler–Wronski effect (SWE). A field evaluation of the long term performance of state-of-the-art crystalline and amorphous silicon photovoltaic modules in Australian conditions is currently being undertaken at Murdoch University. The initial results from this monitoring program are reported. This paper also reports on laboratory and field studies being undertaken on the nature of the Staebler–Wronski effect in amorphous silicon solar cells and how the stability of these cells is affected by different operating conditions. Based on a mechanism for the SWE in a-Si:H solar cells developed as a result of our research we propose a number of possible ways to reduce the Staebler–Wronski effect in a-Si:H solar cells.

The potential, practice and challenges of tertiary renewable energy education on the World Wide Web

The Australian Cooperative Research Center for Renewable Energy (ACRE) through its tertiary training projects seeks to help meet the increasing global need for more tertiary trained scientists, engineers and policy makers with the knowledge and skills to develop and implement renewable and energy efficient systems and policies. As part of this objective it is developing a range of undergraduate and postgraduate university courses in renewable energy technology and systems, energy policy, energy efficiency and greenhouse issues which will be available internationally via the World Wide Web. This paper will present the approach and objectives of ACRE in developing its internationally focused, web-based, renewable energy courses. This includes a description of the course structure and examples of the web-based courses developed so far. A discussion of the potential, the practice and the challenges of offering tertiary renewable energy education on the web is given.

Analysis of the M4,5-N4,5N4,5 spectrum of Ag by Auger photoelectron coincidence spectroscopy

A number of high resolution studies of the Ag M4,5-N4,5N4,5 Auger line shape have been reported. Despite some success in explaining the line shape some important questions as to its nature remain. An Auger photoelectron coincidence spectroscopy study of the metallic Ag M4,5-N4,5N4,5 Auger line, collected in coincidence with the 3d5/2, 3d3/2 and 3p3/2 photoelectrons, is presented. This enables a study of the electron correlation effects and complex Auger decay processes in the Auger emission of a representative 4d transition metal.

Studies of photodegradation in hydrogenated amorphous silicon

IR absorption spectroscopy was used to study light-induced structural changes in hydrogenated amorphous silicon (a-Si:H) films. Our results suggest that illumination causes migration of H atoms from the interior of the film towards the illuminated surface. As a consequence, a transformation occurs in the bulk of the material leading to the formation of dangling bonds in the i-layer which could act as traps for minority carriers in solar cells. Using these results, we have formulated a model for the photodegradation of a-Si:H alloys.

More Auger photoelectron coincidence spectra from copper

We have recently re-built our Auger photoelectron coincidence spectroscopy (APECS) system at Murdoch University. The new instrument counts at much higher rates and with greater energy resolution. With this we have looked again at the APECS spectra from Cu. We have been able to see more clearly the L2–L3V–VV(V) Coster–Kronig satellite and, in a reverse experiment, to find out which parts of the photoelectron spectrum are responsible for the satellite. The data also show the importance of shake-up/off processes in the background of the L3–VV line. We will present information on the changes we have made to the apparatus as well as the implications of the data we have collected with it.

Optical modeling of finely textured amorphous silicon solar cells

It has long been known that the use of finely textured transparent conducting oxide layers substantially improves the performance of thin film amorphous silicon (a-Si:H) solar cells. Major efforts to understand the nature of this effect and to fully capture its potential have been made by researchers using advanced modeling techniques. In this work, modeling the oblique angle optical performance and use of an effective medium approximation to simulate microrough interfaces suggests that effective interface grading makes a significant contribution to optical enhancement.

Simulation of the electronic and vibrational structure of hydrogenated amorphous silicon using cluster models

A set of simple models of hydrogenated amorphous silicon (a‐Si:H) consisting of hypothetical silane molecules with diamond or similar lattices was studied by the semiempirical AM1 method. Densities of states and infrared spectra were calculated for the silane molecules and similar molecules with dangling bonds disorder, and with boron or phosphorus substitution to simulate doping. Some examples are presented, and a comparison is made with experimental properties of a‐Si:H. It is proposed to use these models in a study of the Staebler–Wronski photodegradation of a‐Si:H and other aspects of amorphous silicon technology.

An experimental and theoretical study of Auger lineshapes in hydrogenated amorphous silicon structures

Simple models of hydrogenated amorphous silicon (a-Si : H) consisting of hypothetical silane molecules with diamond or similar lattices were studied by the semi-empirical AMI method. Valence band densities of states (VBDOS) were calculated for the silane molecules with and without the removal of hydrogen atoms. Silicon L1L2.3V Auger spectra have also been obtained using X-ray excitation from disordered crystalline silicon (c-Si), and glow discharge produced a-Si : H. Comparisons have been made between the experimental L1L1.2V Auger spectra of samples with different amounts of hydrogen on the surface and the corresponding VBDOS calculations. Ignoring differences due to matrix elements, good agreement is obtained between the experimental and theoretical spectra and it is shown how the theoretical curves can help interpret changes in the experimental spectra after various treatments. The results provide confirmation that disordering of c-Si leads to an increase in the number of Si p-like defect states at the top of the VB. Furthermore, it is shown that hydrogenation plays an important role in stabilising defects in a-Si by tying off dangling bonds, removing the Si p-like states at the VB edge. This leads to the establishment of new electron energy levels in the VB, with different methods of hydrogenation leading to different bonding configurations. It is shown how the success of these methods provides the basis for subsequent studies of annealing, hydrogenation and photodegradation of a-Si : H alloys.

Recovery of Light Induced Degradation in Amorphous Silicon Solar Cells and Modules

This study concentrates on finding a possible method of annealing amorphous silicon solar modules degraded by prolonged exposure to light. The aim of annealing is the recovery of initial efficiency. This should be done on the modules work site or through simple indoor maintenance. Ideally the annealing temperature should be as low as possible and the annealing time as short as possible. The annealing process of laboratory cells and commercially available triple junction solar modules was performed at temperatures 70 degC-110 degC. The degree of efficiency recovery as a function of temperature and time of exposure to heating was investigated. The influence of factors affecting the rate of degradation and recovery such as short-circuiting, work under load or exposure to light, were also taken into account