In the photovoltaics industry, contacts to crystalline silicon are typically formed by the firing of screen-printed metal pastes. However, the stability of dielectric surface passivation layers during the high-temperature contact formation has turned out to be a major challenge for some of the best passivating layers, such as intrinsic amorphous silicon. Capping of well-passivating dielectric layers by hydrogen-rich silicon nitride (SiNx), however, has been demonstrated to improve the thermal stability, an effect which can be attributed to the atomic hydrogen (H) diffusing out of the interface during firing, and passivating dangling bonds. This paper presents the results of investigations into the influence of two different dielectric passivation stacks on the firing stability, namely SiNy/SiNx (y < x) and Al2O3/SiNx stacks. Excellent firing stability was demonstrated for both stack systems. Effective surface recombination velocities of < 10cm/s were measured after a conventional co firing process on 1.5Ωcm p-type float-zone silicon wafers for both passivation schemes. On the solar cell level, however, better results were obtained using the Al2O3/SiNx stack, where an efficiency of 19.5% was achieved for a large-area screen-printed solar cell fabricated on conventional Czochralski-grown silicon.
The solar photovoltaics market in the United Kingdom was virtually non-existent until April 2010, when the long-awaited feed-in tariff scheme was implemented. Yet, despite coming late to the game, the UK’s solar industry took off immediately, installing more than 80MW in the first 12 months alone. Now, just two years down the line, the market is placed as the world’s eighth largest. This paper will take a look back at how the UK got to this point as well as considering just how bright the future of this fast-paced market will realistically be.
Predicting what will happen to the global PV market is very nearly an impossible task. Its underlying principles are very similar to the dozens of other electronics markets that IMS Research studies, but the key difference in the PV industry is the very close link to, and ultimate dependence on, government policy. In a few years’ time, the introduction, halting or change (or rumoured change) of a single government’s PV policy will have little effect on the global industry, and the huge swings in demand will be less common and less severe. The reasons for this are clear. First, because of geographic diversification in the industry, a single country will account for a smaller portion of the global total (unlike in 2011, when Germany and Italy accounted for more than half of global demand) and thus individual governments’ policy changes will have a smaller impact. Second, if system prices continue to drop rapidly (and IMS Research believes they will), a growing number of regions will achieve the ‘holy grail’ of grid parity and will thus no longer depend solely on government policy to drive their markets.
The purpose of this paper is to give an overview of the use and potential of diamond wire for the silicon-shaping process in the PV industry. The current market and future prospects for helping to meet the goals of 2020’s roadmap of thinner wafers and reduced $/W are described.
The 15th edition of Photovoltaics International hopes to bring some optimism to 2012 by tackling the key factors on how to cope with the current situation. Contributions come from MIT on using TCAD as a viable method for modelling metal impurity evolution; Alternative Energy Investing presents a comprehensive look at materials cost; and efficiency improvements are on offer by ECN. REC Solar and Tata BP Solar report on module lifetime and IMS Research gives us a brief rundown of 2012 global market expectations.
Crystalline silicon solar modules installed in the field are exposed to atmospheric conditions and experience stress, which induces a wear-out phenomenon in various parts of the modules and degrades performance over time. The performance eventually reaches a point where the output power falls below an acceptable level. Thermal cycling (TC) and damp heat (DH) are two important reliability tests for estimating infant failures related to materials and the manufacturing process, as well as providing the information on performance degradation with respect to time. In this study, modules composed of 156mm × 156mm multicrystalline silicon cells were subjected to TC and DH tests. By applying acceleration models, such as the Norris-Landzberg model for TC and the Hallberg-Peck model for DH, the minimum guaranteed life was calculated. The electrical and reliability results were interpreted and explained on the basis of the respective models.
Coupled device and process simulation tools, collectively known as technology computer-aided design (TCAD), have been used in the integrated circuit industry for over 30 years. These tools allow researchers to quickly home in on optimized device designs and manufacturing processes with minimal experimental expenditures.
The PV industry has been slower to adopt these tools, but is quickly developing competency in using them. This paper introduces a predictive defect engineering paradigm and simulation tool, while demonstrating its effectiveness at increasing the performance and throughput of current industrial processes. The impurity-to-efficiency (I2E) simulator is a coupled process and device simulation tool that links wafer material purity, processing parameters and cell design to device performance. The tool has been validated with experimental data and used successfully with partners in industry. The simulator has also been deployed in a free web-accessible applet, which is available for use by the industrial and academic communities.
This paper presents examples of recent process developments at ECN in silicon solar cells on n-type monocrystalline base material. For all PV manufacturers, the challenge is to increase module efficiencies while maintaining low production cost. An effective way to move to higher and more stable efficiencies, using low-cost industrial-type processing, is n-type solar cell technology. The solar cell considered in this paper is the n-pasha cell – a bifacial solar cell with homogeneous diffusions and screen-printed metallization. The n-pasha cell is currently produced on an industrial scale by Yingli Solar; in 2011 a maximum solar cell conversion efficiency of 19.97% was obtained using this cell concept on 239cm2 n-type Cz at the ECN laboratory. The focus of the paper will be increasing efficiency by optimization of the cell process, in particular the front-side metallization, and by improvements to the rear-surface passivation. These two steps have contributed an increase in efficiency of 0.8%, allowing cell efficiencies of 20% to be reached.
As a relative newcomer to the industrial world compared to more mature manufacturing sectors, the PV industry has not yet been subject to consistent environmental regulatory standards internationally. Like all industries that have preceded it, PV manufacturing is seeing its regulatory future evolve as PV producers migrate to different regions of the world. With this global expansion come significantly different levels of regulatory stringency, reflective of local conditions and cultures.
Non-destructive methods for measuring photovoltaic modules are discussed in this paper, with the aim of comparing different quality-assurance methods for different module technologies (e.g. crystalline and thin-film technologies: a-Si, CdTe, CIS). For a complete quality control of PV modules, a combination of fast and non-destructive methods was investigated. In particular, camera-based measurements, such as electroluminescence (EL) and infrared (IR) technologies, offer excellent possibilities for determining production failures or defects in solar modules, which cannot be detected by means of standard power measurements. These methods are applied effectively in quality control and development support, and EL is already an important characterization tool in industry and research. Most short circuits reduce the voltage in their surrounding area and appear dark in EL images. However, as this failure is not always critical and apparent, short circuits are only precisely identifiable in combination with IR measurements. Therefore, to quickly detect at high resolution the most common defects in a PV module, a combination of EL and IR measurements is advisable.
