Technical Papers

The emitter or p-n junction is the core of crystalline silicon solar cells. The vast majority of silicon cells are produced using a simple process of high temperature diffusion of dopants into the crystal lattice. This paper takes a closer look at the characteristics of this diffusion and possible variations in the process, and asks whether this step can lead to optimal emitters or whether emitters should be made with different processes in order to obtain the highest possible efficiency.

Photovoltaic modules are designed to meet the reliability and safety requirements of national and international test standards. Qualification testing is a short-duration (typically, 60-90 days) accelerated testing protocol, and it may be considered as a minimum requirement to undertake reliability testing. The goal of qualification testing is to identify the initial short-term reliability issues in the field, while the qualification testing/certification is primarily driven by marketplace requirements. Safety testing, however, is a regulatory requirement where the modules are assessed for the prevention of electrical shock, fire hazards, and personal injury due to electrical, mechanical, and environmental stresses in the field. This paper examines recent reliability and safety studies conducted at TÜV Rheinland PTL’s solar module testing facility in Arizona.

Solar currently represents less than 0.5% of global electricity generation. However, as renewable electricity gains importance in the US$1 trillion global electricity market, we forecast solar photovoltaic shipments to rise at a compound annual growth rate of 50% for the next four years. We expect an increasing number of countries to promote solar energy as the cost gap between solar and fossil fuel-generated electricity closes. This paper provides an overview of what to expect from the PV market in 2010.

The key to delivering highly efficient solar cells is to absorb as much light as possible from the solar spectrum and convert it effectively into electrical energy. Anti-reflective coatings have served as agents for reducing reflective losses and improving bulk and surface passivation thus enhancing both of the parameters – short circuit current and open circuit voltage of a solar cell. Simulation studies show that an SiN/MgF dual-layer anti-reflective coating is best for a bare cell. This paper takes a closer look at how this coating can reduce the reflectance for a broad range of wavelengths and thus enhance the quantum efficiency of the cell in the blue and red region of the solar spectrum.

Highly conductive transparent films are of significant interest in the field of thin-film photovoltaics. ZnO-based films in particular have attracted much interest due to the low cost of materials with good film properties for CIGS and a-Si/µc-Si solar modules. Investigations have been ongoing at Fraunhofer IST into ceramic ZnO:Al2O3 targets from different manufacturers. This paper presents a comparison of target material, sputter characteristics and film properties of ZnO:Al. Sputter characteristics are in this case determined by voltage and current data showing arcing rates at different power loads and process pressures. ZnO:Al films are deposited by DC magnetron sputtering with various deposition parameters (e.g oxygen flow, total pressure, sputtering power and substrate temperature) and investigated with respect to optical and electrical properties. A correlation between film properties, sputter characteristics and target material can therefore be determined. As it appears that arcing has the biggest influence on film properties, the ceramic target material can be optimized for minimal arcing.

Despite the fall in silicon prices, wafer thickness continues to be reduced. The handling of thin wafers between 120 and 160µm is under research at the Fraunhofer IPA, where gripper-dependent and independent variables were determined as parameters for the handling process. Diverse grippers are tested on an automated test platform. Among these are grippers that are specifically designed for wafer handling, as well as others that are not but are used for wafer manipulation. The test platform includes several different test and handling equipments and utilizes critical parameters that might be required for achieving a high production rate via shortest cycle times to investigate the impact on thin wafers. The first results of the position accuracy measurement in relation to the physical movement parameters and other industrial key figures in ongoing handling research are presented within this paper.

Building-integrated photovoltaics or BIPV is one form of solar electricity that looks set to dominate the solar market in the coming years. The increase in BIPV installations is already evident in some European countries as governments begin to tweak their policies in order to provide a platform for this technology. The past few months have seen countries such as France and Italy make efforts to up the installation rate of this integrated form of solar, increasing the feed-in tariff (FiT) rate quite substantially for BIPV and lowering it for the more common installations such as roof and ground-mounted systems in order to increase the uptake. This BIPV-dedicated section will focus on the new policies implemented in France and Italy, concentrating on France’s policies as a blueprint for others. It will provide a focus on why governments are so keen to increase incentives in favour of BIPV and what the future implications of this market shift will be.

In most complex manufacturing environments, equipment failures dominate. These failures are commonly referred to as ‘fires’ because of the chaos and damage they inflict on factory operations. For example, a key piece of equipment fails, creating a blockage in the production line. One or more personnel are quickly dispatched to fix the problem. The situation is dire, threatening to slow daily product starts and slip output goals. Those working the problem know this failure is of the utmost importance and know if they can just get the machine at an acceptable level, the stress from management will be lifted. Logic leads these personnel to suspect a specific component, which is then replaced. This paper discusses the best method of ensuring that this ‘patching’ of problems does not become part of the regular maintenance routine.

Thin-film module production has proven itself as a forerunner in the race to drive down costs for photovoltaics. The type of semiconductor material used is the most differentiating factor for thin-film photovoltaics, playing the decisive role for determining which core processes are employed and what type of equipment is used. This explains why discussions related to thin-film costs and technologies usually focus on the semiconductor type. However, the effects of glass production, processing and handling are often underestimated: factors such as scaling, yield, unit cost and total cost of ownership of the equipment are defined by the glass-production side of the industry. This paper discusses the challenges faced in glass washing and handling in thin-film PV production.

As polysilicon producers perform expansions and upgrades to increase production and improve operations, plant safety remains critical. Companies should routinely review their safety policies and effectively plan their projects to ensure uninterrupted product supply and create a safe environment for employees and the communities in which they operate. Both the design and the execution of expansion and upgrades to projects are critical as companies strive for minimal down time so that productivity is not affected. Such hazards and scenarios that may hinder and delay start-up, specifically in relation to polysilicon plants, are highlighted in this paper. Furthermore, the paper outlines how best to avoid these situations, offering methods of execution to achieve the three key measures of success: safety, high purity and minimal downtime.