Photovoltaics International Papers

The continued tight supply and high cost of polysilicon, coinciding with the growth in demand for solar energy, has been a key catalyst for the rapid adoption of thin-film technologies in just the last two years. Although the technology has in development for over 15 years, it is only now that thin film has emerged as a viable low cost-per-watt alternative to conventional crystalline silicon cells. Taiwan, a powerhouse in the electronics and microelectronics industries, is also turning its attention to photovoltaics. Playing catch-up is something at which the Taiwanese have proven to be very effective, with a growing emphasis on thin film as a means to become another major centre and net exporter.

In the perpetual struggle to reduce the costs associated with PV energy generation, one aspect of the manufacturing process has potential to shine. To date, the PV sector is dominated by crystalline silicon wafers (90%), which largely use silver as the conducting medium for the front side grid, and to a lesser extent the backside contact. The conducting media are crucial to the overall efficiency of the cell by providing the means for current to flow when sunlight strikes the doped silicon wafer. This paper presents silver as a vital factor in the PV process, and discusses the future industry requirements as well as a projection for the overall silver market for the next eight years.

Back-sheet materials for photovoltaic modules serve several purposes such as providing electrical insulation, environmental protection and structural support. These functions are essential for modules to be safe for people working near them and for the structures to which they are attached. To ensure that all modules meet a minimum set of requirement, they must pass qualifications tests such as IEC 61646, 61215, 61730, and 62108. This paper puts forward the design and composition requirements of back- and front-sheet materials for achieving the highest possible quality performance from PV modules.

The reliability of United Solar Ovonic (Uni-Solar) triple-junction amorphous-silicon thin-film photovoltaic modules is critical to their success in an increasingly competitive PV market. Modules must show useful operating lifetimes of 20 to 30 years, and although module efficiency is very important, the total energy that a module will produce largely depends on its operating lifetime. Thus, module reliability must be evaluated to estimate lifetime and establish customer warranty periods. While real-world outdoor exposure testing is necessary and important, accelerated environmental test methods must also be utilized to provide more rapid feedback regarding failure modes, design flaws and degradation mechanisms. The following paper gives an overview of the methodology used to ensure long-term reliability of Uni-Solar flexible thin-film modules.

Solar enterprises will each be faced with the occasional surplus or lack of solar modules in their lifetimes. In these instances, it is useful to adjust these stock levels at short notice, thus creating a spot market. Spot markets serve the short-term trade of different products, where the seller is able to permanently or temporarily offset surplus, while buyers are able to access attractive offers on surplus stocks and supplement existing supply arrangements as a last resort.

The costs of a photovoltaic installation are driving the market and the need for subsidized schemes, such as feed-in tariffs. Concentrated photovoltaics (CPV) is leading the development of future lowcost renewable energy sources in two ways: on one hand offering high efficiency systems, and on the other, being most capable of reducing manufacturing costs. The idea to decrease the cost of the photovoltaic system using optical elements to focus the radiation into the cell to reduce the size of the cells has been in the mind of the scientists since the 1970s [1]. But, apart from a reduced market, there were several issues that did not allow CPV success at that time. This paper puts forth the proposition that the key is to replace the area of active material, which is the most expensive, with optic elements, which are well known and cheaper.

The rapidly-growing photovoltaic market has placed a strong demand on manufacturers to decrease solar cell production costs. For thin-film solar cells, this can be achieved by increasing substrate sizes to achieve a better productivity and by adding more advanced layer stack systems to enhance the solar cell’s efficiency. Nearly all required layers of the prominent thin-film-based solar cell types (a-Si/µc-Si, CdTe and CI(G)S) can be deposited by using plasma processes. On the one hand, plasma-enhanced chemical vapor deposition (PECVD) is used for the deposition of a-Si and µc-Si layers. On the other hand, magnetron sputtering is used for coating with transparent conductive oxides as ITO (indium tin oxide) and ZAO (aluminium-doped zinc oxide), metallic back contact layers such as Ti, Al and Mo, or components of the compound semiconductor layers such as Cu and In. Magnetron sputter processes use direct current (DC) or pulsed DC, whereas radio frequency (RF) power is used for PECVD processes. Of utmost importance to get a reliable, high-efficiency solar cell is a good uniformity of the deposited layers and the need for the layer to be defect-free. Defects such as particles and splashes are created inside the plasma when an unwanted local discharge - a so-called arc - occurs. This arc can be eliminated by switching off the power supply. The faster this is done, and the less energy that is delivered into the arc, the smaller and more insignificant the defect creation will be. For this reason, as well as for precise control of electrical power, advanced, fast-reacting arc management is very important to attain high-quality solar cell coatings.

The deposition of thin films is a key technology for a large variety of technical and scientific applications. Among them is the deposition of silicon nitride (SiNx) to passivate the surface of silicon solar cells. The SiN film serves several purposes. It is a broadband anti-reflection layer, it serves to saturate dangling bonds and/or other surface states of the silicon, and last but not least, it is a protection layer to prevent alkali ions and other impurities from diffusing into the silicon causing perturbations of the performance of the solar cell. This multitude of properties to be fulfilled at the same time often causes difficulties in assessing the effect of a single process parameter, let alone the task of optimizing the SiN film in all required aspects at the same time. The aforementioned technical features of the SiN film provide the very property that largely determines the aesthetically pleasing appearance of a cell, and hence a PV module, as the colour of the module is determined by the cell composition. In order to complicate things further, there are numerous deposition techniques being applied both on a scientific level as well as in production environments.

Climate change, oil shortage, green energy, energy security – these are some of the global `mega´-topics currently dominating the agenda in the news, in politics and in private lives. One of the industries that has most profited from the ever-growing consciousness about the need to de-carbonize current energy use is the photovoltaic industry. With this economic background, the photovoltaic industry has experienced impressive growth rates in the last decade and is expected to grow at 30% per year over at least the next couple of years. Since its upswing, it has become a multi-billion dollar industry and subject to speculation on stock exchanges worldwide.

The rapid growth of the solar energy industry owes its success to the development and production of mono- and multi-crystalline solar cells. This growth has been limited in recent years due to the lack of available supply of polysilicon, the key raw material for making the wafers that serve as the basis of the solar cell. As a result of this limitation, the price of polysilicon has increased dramatically and this has led to significant new and planned capacity expansions. These new capacity expansion announcements have been highly publicized, with little additional outside focus on other chemicals and materials.