Phosphorus dopant pastes are an attractive alternative to the conventional phosphorus oxychloride (POCl3) dopant source for emitter processing in solar cells, as they allow the fabrication of selective emitters on an industrial scale. In this paper it is demonstrated that single-sided uniform screen-printed emitters, processed with phosphorus dopant pastes, can getter multicrystalline silicon (mc-Si) wafers more effectively than conventional double-sided uniform POCl3 emitters. This result is confirmed by minority carrier lifetime measurements with the quasi-stead-state photoconductance (QSSPC) method. Solar cells with selective emitters were processed using phosphorus dopant pastes on mc-Si wafers and were subsequently characterized. The current-voltage (I-V) results are improved compared to uniform POCl3 emitter solar cells and an increased internal quantum efficiency (IQE) for selective emitter solar cells is demonstrated.
Upgraded metallurgical-grade silicon (UMG-Si), once looked on as a cost-effective and energy-efficient alternative to Si produced via the Siemens route, has experienced a severe regression of late. This has been caused both by the market conditions and by specific physical properties of these materials. Meanwhile, the qualities and the rated influence of negative physical effects have changed partially. Hopes are again rising that these materials, which have to be compensated to meet the desired net doping specifications, might achieve an economical breakthrough instead of long-dreaded low breakdown voltages. In the following paper, we summarize a few of our results on multicrystalline UMG silicon as well as results published by other research groups in the last few years.
The 12th Edition was published in May 2011. Highlights from this edition include Conergy’s in-depth study of MES in PV facilities; University of Konstanz heralds the return of UMG-Si; RWTH Aachen University details the gettering options available for selective emitters; TU Delft presents an overview of breakage issues for silicon wafers and cells; and the University of Toledo outlines the benefits of RTSE in polarized light metroscopy.
Technology computer-aided design (TCAD) is pervasive throughout research, development and manufacturing in the semiconductor industry. It allows very low-cost evaluation of process options and competing technologies, guides process development and transfer to production and supports more efficient process improvement with minimal down time in the factory environment. This paper reviews the use of TCAD in the semiconductor industry and shows, with some illustrative examples, its important enabling role for the PV industry.
Reduction of silicon wafer thickness without increasing the wafer’s strength can lead to a high fracture rate during subsequent handling and processing steps. The cracking of solar cells has become one of the major sources of solar module failure and rejection. Hence, it is important to evaluate the mechanical strength of silicon solar wafers and influencing factors. The purpose of this work is to understand the fracture behaviour of multicrystalline silicon wafers and to obtain information regarding the fracture of solar wafers and solar cells. The effects on silicon wafer strength of saw damage and of grain size, boundaries and triple junctions are investigated, while the effects of surface roughness and the damage layer removal process are also considered. Significant changes in fracture strength are found as a result of different silicon wafer crystallinity and surface roughness. Results indicate that fracture strength of a processed silicon wafer is mainly affected by the following factors: the saw-damage layer thickness, surface roughness, cracks/ defects at the edges and the number of grain boundaries – which all serve as possible crack initiation points. The effects of metallization paste type and firing conditions on the strength of solar cells are also considered, with findings indicating that the aluminium paste type and firing conditions influence the strength of solar cells.
Exceptional demand characterized the PV industry in 2010. Uncertainty regarding incentive schemes in a number of key markets drove global installations, and inverter shipments grew by over 160% as investors and developers rushed to complete projects, fearing that incentives would be reduced or removed altogether. IMS Research estimates that inverter shipments exceeded 20GW in 2010 and sales of small three-phase inverters, rated between 10-20kW, grew by around 200% in 2010. Inverters rated at over 500kW are estimated to have grown at a similar rate, but continue to represent a smaller share of revenues.
This paper presents the Q-Cells research line (RL) as a core of the Reiner Lemoine Research Centre, including the technical set-up, the organization of the operation and current results of cell concepts processed in the RL on a regular basis. Trends of cell parameters for those processes are shown, and a focus is presented regarding the results of our high-efficiency cell concepts for multi- and monocyrstalline material processed in the RL with stabilized record efficiencies of 18.4% and 19.2%, respectively. In addition, we discuss the process flow and the results of a monitoring procedure that is used to check the rear-side passivation quality of the company’s equipment. Results of our current passivation stack show a surface recombination velocity of below Srear < 10cm/s, well suited to fabricating p-type Si solar cells with efficiencies above 20%.
The behaviour of PV markets over the last decade in Europe has taught us that not only it is necessary to optimally design support schemes, but that priority access to the grid for renewable energy sources and the reduction of administrative barriers are the key market drivers for sustainable development and essential for the markets to sustainably develop in the long term. This paper provides an overview of Europe’s PV market performance and delivers policy recommendations by means of EPIA’s PV Observatory model.
Processing silicon substrates for PV applications involves texturing, cleaning and/or etching wafer surfaces with chemical solutions. Depending on the cleanliness of the industrial equipment and the purity of the chemical solutions, surface contamination with metals or organic residues is possible [1]. The presence of trace contamination at PV junctions leads to both mid-level traps and photonic defects, which ultimately cause reduced efficiency and rapid cell degradation. Metallic impurities have a greater impact on PV cell lifetime due to their deeper energy levels in the silicon band gap [2]. On the other hand, non-metallic impurities may modify the electrical activity of PV cells because these species involve complex interactions with the host silicon lattice and its structural defects. In other words, very small amounts of contamination can result in poor PV efficiency. This paper presents an overview of the effects of adding a biodegradable complexing agent in cleaning and rinsing baths to minimize surface contamination and thereby enhance solar cell efficiency.
After the encapsulation step, a c-Si solar module’s output is usually decreased, in comparison to its cells’ power, which is referred to as ‘power loss’. This paper focuses on the various factors that can impact power loss of solar modules, such as solar cell classification, encapsulation material, match of solar cells, the encapsulation process used, and so on. The conclusion indicates that power loss in solar modules can be significantly decreased with a resulting increment of a module’s output by appropriately optimizing those factors.
