This paper presents the status of imec’s work on the use of copper for the main conductor as an alternative to screen-printed silver front contacts in solar cells. This work is motivated not only by the limitations that Ag screen-printed contacts have regarding solar cell efficiency (high contact shading, limited line conductivity, and poor contact resistance to moderately doped emitters), but also by the PV industry's desire to reduce Ag usage for reasons of cost. Despite the potential advantages of Ni/Cu contacts, their commercialization has been limited because of increased process complexity and doubts over the €/Wp advantage and long-term reliability. These three factors all depend on the specific process and toolset and are discussed in this paper. A relatively simple process sequence is described that uses industrial pilot-line tools and consists of: 1) defining the front-contact pattern by ps-UV laser ablation; 2) self-aligned plating of the contacts using Ni/Cu/Ag; and, finally, 3) sintering in N2 for nickel silicidation. The process sequence is applied to 15.6 x 15.6cm2 p-type CZ-Si PERC (passivated emitter and rear cell) solar cells with 120Ω/sq. homogeneous emitters; average cell efficiencies of 20.5% are achieved over more than 100 cells. Cost analysis results are then discussed, indicating that this Ni/Cu process sequence has a lower cost/piece than equivalent screen-printed PERC cells while also providing ~0.5% abs. higher cell efficiency. Thermal-cycling and damp-heat reliability data that meet extended (1.5 x) IEC 61215 criteria for singlecell laminates and small modules are reported. The improved efficiency potential of applying this metallization sequence to rear-junction n-type PERT (passivated emitter and rear totally diffused) cells is discussed and preliminary results are given.
For more than a decade, the growth in PV markets surpassed expectations. Then, in 2012, the European market declined for the first time compared with the previous year. As policymakers’ support for PV hesitates over the costs to society of this technology, it is timely to take an overview of the social costs and benefits, also referred to as the ‘external costs’, of PV electricity. In this article, these costs are put into perspective visà- vis those associated with conventional electricity-generating technologies. The external costs of electricity can be broken down into: 1) the environmental and health costs; 2) the costs of subsidies and energy security; and 3) the costs for grid expansion and reliability. Included in these costs are the increased insurance, health, social and environmental costs associated with damages to health, infrastructure and environment,
as well as tax payments that subsidize producers of electricity or fuels, their markets and the electricity infrastructure. A life cycle assessment (LCA) of the environmental impact is used in the quantification of the associated environmental and health costs. Because the environmental footprint of PV electricity is highly dependent on the electricity mix used in PV module fabrication, the environmental indicators are calculated for PV electricity manufactured using different electricity mixes, and compared with those for the European electricity mix (UCTE), and electricity generated by burning 100% coal or 100% natural gas. In 2012$, coal electricity requires 19–29¢/kWh above the market price, compared with 1–1.6¢/kWh for PV manufactured with 100% coal electricity. The sum of the subsidies, avoided fossil-fuel imports and energy security, and the economic stimulation associated with PV electricity deployment, amounts to net external benefits. Integrating high penetrations of renewables, with the same reliability as we have today, appears to be fully feasible and within the cost horizons of the current activities of system operators.
Economic issues are the driving forces behind PV adoption. Even technological advances are measured against their impacts on cost per watt, levelized cost of energy (LCOE), and total cost of ownership for energy (TCOe™). This sixth paper in a series covering business analysis for PV processes looks at two approaches to manufacturing thin-film copper-indium-gallium-diselenide (CIGS) PV – sputtering and co-evaporation – and their potential areas for cost improvement.
The aim of this paper is to shed some light on what difference the quality of a PV product makes to the customer and how much effort is required to deliver it. From the customer’s point of view, the quality of a PV product is key to a worthwhile investment, since the value of a PV system is defined by its cost compared with its yield over the entire lifetime, or the levelized cost of electricity (LCOE). But while many manufacturers make more or less the same promises, in this paper a closer look is taken at what is really involved in living up to those promises. If quality is understood to be a fundamental attitude that is reflected in every single process along the entire value chain, only then will this eventually lead to high-quality products and services. The paper discusses in detail the principles, methods, tests and processes required to secure a superior quality brand.
There have been encouraging signs in recent months of changing fortunes for PV equipment suppliers after a difficult period of consolidation. Shipment figures, actual and forecast, have in many instances seen an upswing, as booming markets in Japan, China and the US continue to drive demand, even as some European markets continue to dwindle. It’s probably too early to call the beginnings of a new PV technology buy cycle, but it seems more a case of ‘when’ rather than ‘if ’ now, and analysts have pointed to mid-2014 as the likely point when supply and demand will be in some kind of equilibrium. Clearly the implication of this is that if demand continues to rise beyond this point, supply will have to keep up, so manufacturers will have to invest in new capacity.
Passivated emitter and rear cells (PERC) are considered to be a next generation of industrial solar cells, and several companies have already started pilot production. The much-reduced rear-surface recombination in PERC cells requires improvements to the front side, for example the emitter, in order to further increase the conversion efficiency in the future. This paper presents an evaluation of the emitter technologies of three industrially applicable PERC cell concepts: 1) with an ion-implanted emitter, 2) with a chemically polished rear surface, and 3) with a selective emitter formed by gas phase etch-back (GEB). The results are compared with a reference high-efficiency POCl3-diffused PERC cell. The three industrial PERC concepts utilize lean industrially applicable process flows which reduce the phosphorus concentration at the wafer surface.
Accordingly, when compared with the POCl3-diffused emitter, the ion-implanted and GEB emitters obtain significantly lower emitter saturation current densities of 40 to 60fA/cm2 for emitter sheet resistances of 90 to 130Ω/sq. When applied to large-area PERC cells with screen-printed metal contacts, the ion-implanted and GEB emitter cells demonstrate up to 10mV higher open-circuit voltages than the POCl3-diffused reference PERC cell, and achieve conversion efficiencies of 20.0 and 20.3%, respectively. The next steps in further increasing the efficiency are outlined.
According to the ITRPV (International Roadmap for PV), a large fraction of future solar cells will be n-type and rear-contact cells with the highest efficiencies and fabricated using low-cost processes. As the standard p-type silicon solar cell in mass production is completely optimized and has therefore reached its cost limit, it is currently very difficult for new solar cell concepts to be cost effective from the outset when introduced into production. Consequently, in the current market situation, the introduction of new solar cell concepts to the market is not straightforward. The only way to achieve this is to use the fully adapted standard processes employed in today's manufacturing lines and only upgrade them with a few industrially approved process steps – such as laser ablation and boron diffusion – in order to implement low-cost device structures with stable efficiencies well above 20%. This paper gives an overview of n-type cell concepts already present on the market and of promising technologies ready for pilot production; the latter were summarized and discussed at the 3rd nPV workshop in April 2013 in Chambéry, France. The consequences for module manufacturing, as well as for measurement techniques and for requirements in respect of new standardization for cell and module characterization, will also be discussed..
As the PV capacity of utility systems increases, utility planners and operators are becoming more and more concerned about the potential impacts of power supply variability caused by transient clouds. Utilities and control system operators need to adapt their planning, scheduling and operating strategies to accommodate this variability while at the same time maintaining existing standards of reliability. Effective management of these systems, however, requires a clear understanding of PV output variability and the methods to quantify it. The present objective is to develop analytical methods and tools to quantify PV fleet output variability. This paper presents a method using location-specific inputs for estimating correlation coefficients, and discusses the key findings that resulted from applying the method to three separate geographical regions in the USA. The approach has potential financial benefits for systems that are concerned about PV power output variability, ranging from individual distribution feeders to state-wide balancing regions.
Whether in the USA as a part of a manufacturing resurgence or elsewhere in the world, solar producers need to be smarter than ever about where they choose to locate new operation centres. Solar manufacturing site selection
demands analytical rigour. The intent of this article is to share strategies and tools that can help owners make the best informed choices about where to locate new manufacturing operations.
Even in the competitive and turbulent present-day PV market, thin-film PV modules based on copper indium gallium selenide (CIGS) have good prospects for capturing a growing market share. Three important factors support the survival and growth of CIGS technology on the market: 1) proven lab results demonstrate considerable room for improvement of conversion efficiency; 2) the potential for cost reduction is high (reduced equipment CAPEX as well as reduced material and BOS costs); and 3) a high degree of freedom in the choice of substrate material and shape
enables efficient application of the technology. These factors should be realized using more-generic or standardized CIGS production equipment to reach economy of scale. Examples of novel and improved strategies for cost-efficient thin-film deposition and absorber formation are presented in this paper. Within the framework of a new thin-film PV research alliance under the name Solliance, a CIGS demonstrator line has recently become available for accelerating R&D of cost-effective processes and equipment, and for demonstrating their capabilities in improving CIGS in terms of
product performance and lifetime..
