Emitter formation is one of the most critical processes in the fabrication of silicon wafer solar cells. The process for standard emitter formation adopted in the photovoltaic industry is tube-based diffusion, using phosphorus oxychloride as the dopant source. A potentially low-cost alternative that typically results in lower solar cell efficiencies is in-line diffusion, using phosphoric acid as the dopant source. The Solar Energy Research Institute of Singapore (SERIS) recently developed a technique called the ‘SERIS etch’, a non-acidic etch-back process technology that provides a controllable, uniform and substantially conformal etch-back suitable for solar cell processing. By using the SERIS etch, efficiencies of up to 18.7% have been demonstrated for omogeneous-emitter silicon wafer cells; a 0.4%abs efficiency improvement has also been achieved for a unique selective-emitter approach exploiting this novel etch. All work was carried out on industrial-grade p-type Cz wafers with conventional screen-printed metallization and a full-area aluminium back-surface field (Al-BSF). With Al local BSF (LBSF) homogeneous-emitter solar cells, efficiencies of 19.0% were achieved using in-line emitter diffusion and the SERIS etch, a 0.7%abs efficiency increase over the baseline efficiency at the time. To the authors’ knowledge, these are the highest solar cell efficiencies ever reported for in-line-diffused silicon solar cells. Moreover, the SERIS etch is a costeffective alternative to generating pyramid-textured surfaces without using conventional metal-assisted siliconetching processes.
Despite the drop in price of silicon wafers, they are still one of the main factors influencing the cost and performance of Si-based solar cells. These two consequences have initiated a growing commercial interest in mono-cast (castmono, mono-like or quasi-mono) Si wafers, supported by R&D in the areas of material characterization, correlation with cell efficiencies, and mono-cast material use in advanced cell technologies. This paper gives a broad overview and comparison of commercially available grades of mono-cast material from different suppliers. The performance of the material from production in high-throughput screen-printing lines, as well as an analysis of the main material characteristics influencing these results, is presented. A characterization using a lifetime tester and a photoluminescence (PL) imaging tool has shown that not only grain boundaries but also dislocations could cause a drop in cell Voc of more than 15mV. Wafers with large surface areas of Si lattice planes, when processed with anisotropic texturing, could yield an increase in Isc greater than 400mA for 6" substrates, as compared to the isotropic-textured equivalents. Furthermore, when a high-grade mono-cast material processed in anisotropic texturing was compared with CZ mono material from the same supplier and of the same resistivity, light-induced degradation (LID), presented as combined Voc and Isc degradation, was only one-third of that in CZ material. However, although mono-cast material has the potential to increase cell line performance to the same level as that gained by important process and technological improvements, it imposes very high requirements for better material sorting in order to achieve stable cell electrical performance and module aesthetics acceptable to the market.
Because most of the costs of developing a PV power plant are paid before any energy is generated, optimizing the energy production from the plant is critical during plant design. Lost energy and increased operations costs due to non-optimal site characterization, technology choice, plant design, installation and other factors result in lower
energy production and a higher levelized cost of energy (LCOE). Many design decisions are based on results from PV performance models. Current PV performance models can represent only some of the differences between sites, technologies, designs and operations choices. This paper provides a description of what is currently known about
some of the performance tradeoffs faced by PV plant designers and operators. It presents a vision for improving PV performance models so that in the near future a full optimization can be carried out to improve the performance and lower the costs of PV plants. This will hasten the adoption of clean energy production from the sun.
Economics will always play a crucial role in the way PV technology advances. However, the current generation of products is facing substantial business challenges in the attempt to scale the product technologies. This paper is the fifth in a series covering business analysis for PV processes. The methods applied in these papers fall into two categories: cost of ownership (COO) modelling and cost and resource modelling. Both methods examine the business considerations associated with the adoption of new processes, tools or materials. This is more critical than ever. Nearterm issues – in some cases the survival of the business – heavily influence today's decision processes. This paper tries to identify the areas that it is thought will produce the largest near-term paybacks. The areas identified are n-type wafers, Al2O3 passivation and copper metallization.
This paper provides an overview of reducing the ‘soft costs’ of solar, with a focus on driving down the cost of balance of system (BOS) and operations, primarily in commercial-scale installations. Attention is drawn to the internal data and information on specific case studies/best practices that can be replicated by other companies. Mainstream Energy (which supports three business units – REC Solar, AEE Solar and SnapNRack) aims to simplify system design and configuration by utilizing new technologies and streamlining internal processes to reduce total system cost – and take solar to the mainstream.
This paper provides an overview of reducing the ‘soft costs’ of solar, with a focus on driving down the cost of balance of system (BOS) and operations, primarily in commercial-scale installations. Attention is drawn to the internal data and information on specific case studies/best practices that can be replicated by other companies. Mainstream Energy (which supports three business units – REC Solar, AEE Solar and SnapNRack) aims to simplify system design and configuration by utilizing new technologies and streamlining internal processes to reduce total system cost – and take solar to the mainstream.
Economic success in operating PV systems depends essentially on the likelihood of their long-term operation and their delivery of the expected energy yield. These requirements, for which a lifetime of 20–25 years is often assumed, are demanding and cannot be met without preparation. Preconditions are the acceptable quality and long-term stability of the products employed (particularly the PV modules, but also all other components and materials) and the absence of damage to these items during transport and handling. Moreover, PV systems must be professionally planned and properly implemented. This includes considering energy yield assessments not only in the initial estimation of the energy yield, but also in the subsequent planning for concrete implementation. In addition, professional operational management and appropriate maintenance measures will ensure operation with maximum availability. Yield insurance policies can safeguard profitability and render the risks calculable; various models exist for this purpose and these must be carefully tested. It is important that the insurances services also cover the possible insolvency of the responsible system and component suppliers.
Electroluminescence (EL) imaging for photovoltaic applications has been widely discussed over the last few years. This paper presents the results of a thorough evaluation of this technique in regard to defect detection in photovoltaic modules, as well as for quality assessment. The ability of an EL system to detect failures and deficiencies in both crystalline Si and thin-film PV modules (CdTe and CIGS) is thoroughly analyzed, and a comprehensive catalogue of defects is established.
For crystalline silicon devices, cell breakages resulting from micro-cracks were shown to pose the main problem and to significantly affect the module performance. A linear correlation between the size of the breakages and the power drop in the module was established. Moreover, mechanical stress and temperature change were identified as the major causes of the proliferation of cracks and breakages. For thin-film modules, EL imaging proved the existence of an impressive reduction in the size of localized shunts under the effect of light-soaking (together with a performance improvement of up to 8%). Aside from that, the system voltage was applied in order to monitor transparent conductive oxide (TCO) corrosion effects and laser-scribing-induced failures, as well as several problems related to the module junction box in respect of its sealing and the quality of its electric connectors.
Because potential-induced degradation (PID) can cause power losses of more than 30% for modules out in the field, there has already been an extensive effort placed on avoiding this adverse phenomenon. A key feature at the cell level is the silicon nitride (SiNx) anti-reflective coating (ARC). Apart from the known dependency of PID susceptibility on the refractive index, the impact of the deposition parameters has also been under investigation. This paper illustrates the influence of different silicon nitrite layers and their ability to prevent PID. A large number of cells and modules were therefore manufactured, differing only in the type of ARC. The modules were subsequently PID tested under three different climatic conditions, and acceleration factors and activation energies were determined from these tests. In addition this paper presents the results of addressing the weak-light performance and the hot-spot risk of panels after PID exposure. Finally, the reversibility of PID was also investigated in relation to the state of degradation of these samples.
Since the demonstration of the first CuInSe2 solar cell in 1974 by scientists at Bell Laboratories, a lot of effort has been put into the development of cost-effective processes for highly efficient Cu(In,Ga)(Se,S)2 – or CIGS – solar cell devices. In 2012 these efforts led to the first gigawatt CIGS solar module production facility operated by Solar Frontier, a company that has a long history in R&D and originates from ARCO Solar, who developed the first commercial CIGS solar modules at the beginning of the 1990s. However, several start-up companies employing CIGS technology are presently struggling in the currently harsh market environment. Even though world-record laboratory solar cells now demonstrate 20.3% efficiency using a three-stage co-evaporation process, and full-size modules achieve 14.6% employing a similar method, efforts in research and development are more important than ever in order to increase cell efficiency, to bridge the gap between cell and module efficiencies, and to develop cost-effective and robust manufacturing processes. This paper gives an overview of current research topics under investigation by research institutes and industry, with a main focus on CIGS absorber formation. Along with other research results published by groups all over the world, this paper covers recent research results obtained at the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB) and briefly mentions the work of the Photovoltaic Competence Center Berlin (PVcomB), a joint initiative of the Technical University of Berlin (TU Berlin) and HZB.
