The three most viable thin-film photovoltaic technologies – cadmium telluride (CdTe), copper-indium gallium (di)selenide (CIGS), and amorphous silicon (a-Si) – continue to mature and grow technologically and in market stature. But apart from the dominance shown by CdTe leader First Solar, the rest of the TFPV manufacturers have had a fairly difficult time making significant commercial inroads as the price of mainstream crystalline-silicon modules plummeted over the past couple of years. Other factors delaying the long-predicted age of thin film include bankability challenges and difficulties in reducing production and system costs. Yet entrants in all three thin-film categories have reason for optimism, as they push toward a competitive market position. This paper provides an overview of the current status of the thin-film PV sector and its players, offering insights into why certain companies might emerge successfully in the years ahead.
As it makes its way towards a non-subsidised market, the photovoltaic sector has to deal with decreasing margins. To ensure investment goals are met in spite of this, it is imperative that PV power plants generate optimal yields. Comprehensive quality assurance for PV power plants covers all phases of the completion process from the planning to system operation. This article explains the extent of standard quality assurance measures that include yield assessments, module measurements, system testing and yield monitoring. It outlines the potential of linking these quality assurance measures and stresses the importance of the measures themselves being of high quality. Up-to-date scientific findings from Fraunhofer ISE are presented in order to further optimise quality assurance measures.
Magnetron-sputtered ZnO:Al is often used as a front contact in thin film silicon solar cells due to its transparent conductive oxide (TCO) properties that allow texturization by chemical etch processes to introduce light trapping. The transparency, conductivity, and surface texture after etching depend strongly on the sputtering conditions. Consequently, the typical preparation method is to find the right balance in TCO properties and light scattering, leading to a very narrow sputtering parameter window. It is preferable to separate the electro optical optimization from that of texturization to allow for a larger process window and improve ZnO:Al film properties further. This paper presents some methods of controlling the surface features using various mixtures of two step etching processes in aqueous solutions of HF and HCl. Results include methods for controlling the density of craters, texturizing compact ZnO:Al films, and fabricating novel modulated surfaces with more than one characteristic feature size. The two step etch process enables the creation of good surface textures even on high rate material that, via state of the art HCl etching, tend to lead to poor solar cell performance.
A hydrogenated amorphous Si (a-Si:H) film, combined with a silicon nitride (SiNx:H) capping layer and a post-deposition anneal, can hugely enhance the surface passivation on crystalline silicon wafers. In this work, the influence of various deposition temperatures of a-Si:H films on the thermal stability of a-Si:H/SiNx:H stacks and a possible mechanism are discussed. Both minority carrier lifetime measurement and grazing-angle XRD were employed to study the thermal stability of a-Si:H/SiNx:H stacks, and the results are interpreted in terms of dihydrides concentration and epitaxial crystallization. With an appropriate thermal treatment, the a-Si:H film deposited at 130°C and capped by SiNx:H showed better passivation performance than 200°C-deposited a-Si:H/SiNx:H stacks, but under an excessive thermal budget the former showed more severe degradation of carrier lifetime. The more dihydride-rich composition within 130°C-deposited a-Si:H/SiNx:H stacks could be regarded as providing more effective intermediates for hydrogen interchanges, but on the other hand, it is also more susceptible to epitaxial crystallization.
Highly conductive transparent films are of significant interest in the field of thin-film photovoltaics. The solar cell type defines the necessary properties of the TCO used, as, besides the obvious qualities of transparency and conductivity, stability and morphology are important. The most significant properties of these aspects for front contacts in amorphous/microcrystalline silicon tandem, CIGS and CdTe solar cells are presented in this paper. Commonly used deposition techniques like CVD and sputter technology are described herein, focusing on particular techniques like SnO2:F and ZnO:B (CVD) and ZnO:Al (sputtering). New developments of deposition methods are also discussed.
Case in point: SolFocus’s recently dedicated 1MW (AC) high-concentrator photovoltaic installation located on the campus of Victor Valley College in the high desert of Southern California northeast of Los Angeles, which is the largest (H)CPV deployment in North America to date and the Mountain View, CA based company’s biggest project as well.
The photovoltaic market, which is dominated by polysilicon-based crystalline solar cells, has been developing rapidly, with growth rates in the double-digit range for several years. In order to meet increasing demand for hyperpure polysilicon, manufacturers need to adhere to environmentally-friendly production processes with low energy consumption. This article highlights the key processes needed to manufacture hyperpure polycrystalline silicon and explores the related challenges and solutions for sustainable polysilicon production. Our findings prove that only an intelligent interaction of all necessary process steps fulfils the requirements for minimized production residue volumes and low energy consumption. Totally integrated production loops for all essential media are prerequisite to reach these targets. Once implemented, these highly efficient production processes serve as an excellent platform technology for the continued healthy growth of the PV industry.
This paper describes a methodology used to establish reliability of a CIGS thin-film photovoltaic module component based on identification of a failure mode through product thermal-cycling. The initial observation of the failure is described as part of a larger reliability program that progresses from failure mode and effect analysis through a test-tofailure program that has an objective of understanding the ultimate consequence of specific applied stresses on product performance. Once the specific failure mode was discovered, four means of characterizing the mode were applied and are discussed: tensile testing and material analysis, computer modelling, coupon rapid thermal cycling, and mechanical fatigue testing. This work identified the relevant root cause for failure and facilitated a materials change, which itself was subjected to an accelerated testing program to quantify the improvement and determine success of the design. The means of verifying success included meeting an endurance thermal-cycle limit for a collection of samples and subjecting corrected designs to a mechanical fatigue test, where the correlation between thermal cycle and mechanical fatigue were compared using Weibull analysis.
A recent spate of solar cell efficiency gains and record results underline the continued efforts to boost conversion efficiencies, which are at the core of reducing cost-per-watt goals. However, bringing such technology into the mainstream volume production world at little or no increase in manufacturing cost will prove more challenging. This paper takes a look at the current mainstream c-Si cell metallization efficiency developments that are starting to enter volume production with a promise of 20% cell efficiencies and low manufacturing costs.
This paper presents and discusses the merits of layout, systems and options for exhaust treatments in PV cell production. Such treatments usually comprise central acid scrubbing, NOx scrubbing, Volatile Organic Compound (VOC) removal and several local treatments for dust, silane, and VOCs, while caustic scrubbing is an option for monocrystalline PV cell production. As direct and indirect major emissions from typical production steps have already been identified [1], this article focuses on a full emission pattern and identifies two sectors, VOC and NOx treatment, as most important for environmental impact analysis.
