Institute for Solar Energy Research Hamelin

Hameln, Germany

Institute for Solar Energy Research Hamelin

Hameln, Germany
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Agency: European Commission | Branch: H2020 | Program: RIA | Phase: LCE-07-2016-2017 | Award Amount: 6.62M | Year: 2016

The DISC project addresses the need to reduce the consumption of fossil fuels by developing key technologies for the next generation of high-performance photovoltaic (PV) solar cells and modules, allowing ultra-low solar electricity costs with minimum environmental impact. DISC focuses on the only way to fully exploit the potential of silicon to its maximum: through the use of carrier selective junctions, i.e., contacts which allow charge carriers to be extracted without recombination. Such contacts allow for simple device architecture as considered in DISC - non-patterned double-side contacted cells which can be fabricated within a lean process flow, either by upgrading existing or within future production lines. In DISC, a unique consortium of experienced industrial actors will collaborate with a set of institutes with demonstrated record devices and worldwide exceptional experience in the R&D field of carrier selective contacts. DISC will target efficiencies >25.5% on large area cell and >22% at module level while demonstrating pilot manufacturing readiness at competitive costs. Together with a reduction of non-abundant material consumption (Ag, In), with an enhancement of the energy yield, with modern module design ensuring outstanding durability, DISC will provide the key elements for achieving in Europe very low Levelized Costs of Electricity between 0.04 0.07$/kWh (depending on the irradiation), with mid-term potential for further reduction, making solar one of the cheapest electricity source. The high efficient PV modules developed in DISC are predestined for rooftop installations, i.e., neutral with respect to land use aspects. A life cycle approach applied in DISC prevents the shifting of environmental or social burdens between impact categories. DISC has a chance to contribute towards mitigating the impacts of climate change, improving energy access and towards bringing Europe back at the forefront of solar cell science, technology and manufacturing.

Agency: European Commission | Branch: FP7 | Program: CP | Phase: ENERGY.2013.2.1.1 | Award Amount: 10.26M | Year: 2013

The European photovoltaics PV market still represents the predominant share of worldwide installations and electricity generated from PV is becoming increasingly competitive, with an average levelized cost of energy (LCOE) estimated to be between 0.100.16 /kWh in 2011 . This constant reduction of LCOE means that the European industry can only regain its competitiveness with (i) a concomitant reduction of production and investment costs (current net price level ~0.81.0 /Wp today) in Europe in order to face the strong price competition of emerging countries (China and Taiwan), (ii) investment in novel advanced industrial processes allowing for high efficiencies and low-cost device production (iii) the development of high-end tools and processes which are more difficult to master and duplicate, securing a technology leadership. These conditions are necessary to ensure sustainable PV technology production in Europe and the construction of a robust European PV industry able to beat international competition. However, ultra-high-efficiency PV devices require manufacturing processes that are increasingly complex, which results in an increase in the related investment and fabrication costs. Given that the market still requires a reduction of the technology price, we are left with a paradox, and we must find ways to produce high-efficiency devices with competitive industrial processes. The concept proposed by the HERCULES project is to develop innovative n-type monocrystalline c-Si device structures based on back-contact solar cells with alternative junction formation, as well as related structures including hybrid concepts (homo-heterojunction). These concepts are the most promising technologies to reach ultra-high efficiencies with industrially relevant processes. The HERCULES strategy is to transfer the developed processes to the industrial scale by considering all major cost drivers of the entire manufacturing process chain of modules.

Schmidt J.,Institute for Solar Energy Research Hamelin | Schmidt J.,Leibniz University of Hanover | Titova V.,Institute for Solar Energy Research Hamelin | Zielke D.,Institute for Solar Energy Research Hamelin
Applied Physics Letters | Year: 2013

We characterize the electronic properties of crystalline silicon (c-Si)/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) junctions by means of contactless carrier lifetime measurements. The measurements demonstrate that this type of heterojunction has an unexpectedly high open-circuit voltage (Voc) potential exceeding 690 mV, making it relevant for the implementation into high-efficiency c-Si solar cells. Hybrid n-type c-Si solar cells featuring a PEDOT:PSS hole-transport layer on the front reach an energy conversion efficiency of 12.3%. We observe a humidity-related degradation in cell efficiency during storage in air. The degradation is reduced by capping the entire device by an atomic-layer-deposited aluminum oxide film and is completely avoided in a dehumidified environment. © 2013 AIP Publishing LLC.

Brendel R.,Institute for Solar Energy Research Hamelin | Brendel R.,Leibniz University of Hanover
Progress in Photovoltaics: Research and Applications | Year: 2012

Modeling of transport and recombination of charge carriers in solar cells is useful for understanding and improving the device performance. We implement the fully coupled transport equations for electrons and holes into the finite-element partial differential equation solver COMSOL. The dopant-diffused surface regions such as junctions, floating junctions, or back surface field layers are treated as conductive boundaries of the volume in which the semiconductor equations are solved. This so-called conductive boundary (CoBo) model characterizes diffused layers by their sheet resistances and diode saturation current densities. Both are directly experimentally accessible. The CoBo model exhibits excellent numerical stability and enables two-dimensional simulations on a laptop. We find agreement when testing the two-dimensional COMSOL implementation of the CoBo model for one-dimensional devices against simulations using the code PC1D. We apply the CoBo model to elucidate how the sheet resistance of diffused vias impacts the power conversion efficiency of emitter wrap through solar cells. Copyright © 2010 John Wiley & Sons, Ltd.

Jung V.,Institute for Solar Energy Research Hamelin | Kontges M.,Institute for Solar Energy Research Hamelin
Progress in Photovoltaics: Research and Applications | Year: 2013

Rear sides of crystalline silicon solar cells are usually covered with aluminum on which it is difficult to solder. To ease soldering, we present a durability study for a Ni: V/Ag stack on evaporated Al as rear-side metallization. We adapt this cost-effective metallization stack from the microelectronic industry and investigate it as metallization for silicon solar cells. Here, a long-term stability of the metallization and of the solder joint must be guaranteed for 25 years and is therefore evaluated in detail by thermal aging experiments. During this experiment, the mechanical stability of the solder joints is measured. The chemical stability and the intermetallic compound (IMC) growth within the solder joints are examined by secondary electron microscopy, backscattered electron imaging, and energy dispersive X-ray analysis. Experiments with either a Sn-Ag-coated copper tab or pure Sn-Ag solder show two different sorts of IMCs at the Ni: V/Solder interface. With the copper tab, a Cu-Ni-Sn compound, presumably (Cu1 - xNix) 6Sn5, grows at the Ni/solder interface, whereas in case of a pure Sn-Ag solder, a Ni-Sn compound grows, which is likely to be Ni 3Sn4. Analysis of the reaction kinetics leads to activation energies of 77 and 42 kJ/mol, respectively, for a diffusion-controlled IMC growth. By using temperature histograms of PV modules in the field, the necessary minimum Ni: V layer thickness is estimated: without a copper tab up to 1.6 μm Ni and with a copper tab less than 0.2 μm may be consumed by IMC formation during 25 years of lifetime. Copyright © 2012 John Wiley & Sons, Ltd. A Ni: V/Ag stack on evaporated Al is investigated as rear-side metallization for silicon solar cells by a thermal aging of solder joints on this metallization. Depending on the presence of Cu on top of the solder, varying intermetallic compounds are formed at the Ni: V/solder interface. By analyzing the reaction kinetics and taking module temperature histograms into account, the necessary minimum Ni: V layer thickness for 25 years lifetime is estimated. Copyright © 2012 John Wiley & Sons, Ltd.

Bertram E.,Institute for Solar Energy Research Hamelin
Energy Procedia | Year: 2014

Different concepts of solar assisted heat pump systems with ground heat exchanger are simulated according to IEA SHC Task44/HPP Annex38 reference conditions. Two aspects of the concepts are investigated using TRNSYS simulations. First, the solar impact on system efficiency is assessed by the seasonal performance factor. Second, the solar impact on the possible shortening of the ground heat exchanger is evaluated by the minimum temperature at the ground heat exchanger inlet. The simulation results reveal diverging optimums for the concepts. The direct use of solar energy clearly achieves the best effect on the efficiency improvement. A simple domestic hot water system reaches a seasonal performance factor of 4.5 and solar combi-systems seasonal performance factors up to 6. In contrast, the use of solar energy on the cold side of the heat pump achieves the best effects on the shortening of the ground heat exchanger of up to 20%. Two highly sensitive influences are investigated with the developed transient system model. First, the minimum allowed heat source temperature is varied. Here 1 K equals a variation of 0.25 in the seasonal performance or of around 10% ground heat exchanger length. Second, the ground heat exchanger model is simulated without and with a pre-pipe that improves the transient model behavior. The influence of this pre-pipe on the SPF is small for conventionally designed ground heat exchangers, but of around 2 K for the minimum inlet temperature. Therefore, the dynamic model quality reveals potential to reduce the size of the ground heat exchanger corresponding to investment costs.

Werner F.,Institute for Solar Energy Research Hamelin | Schmidt J.,Institute for Solar Energy Research Hamelin
Applied Physics Letters | Year: 2014

We manipulate the negative fixed charge density Qf at the c-Si/Al2O3 interface by applying a bias voltage in a metal-oxide-semiconductor configuration or by depositing corona charges onto the Al2O3 film. A significant increase of the negative fixed charge density from |Qf| = 4 × 1012 cm-2 to values above 1013 cm-2 is observed for surface Fermi energies close to or within the silicon conduction band. The additional charges are shown to be partly unstable under annealing or changing the polarity of the bias voltage. Our experimental data are best described by assuming at least three different types of charge traps responsible for the formation of the negative fixed charge density at the c-Si/Al2O3 interface. © 2014 AIP Publishing LLC.

Richter A.,Fraunhofer Institute for Solar Energy Systems | Glunz S.W.,Fraunhofer Institute for Solar Energy Systems | Werner F.,Institute for Solar Energy Research Hamelin | Schmidt J.,Institute for Solar Energy Research Hamelin | Cuevas A.,Australian National University
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

An accurate quantitative description of the Auger recombination rate in silicon as a function of the dopant density and the carrier injection level is important to understand the physics of this fundamental mechanism and to predict the physical limits to the performance of silicon based devices. Technological progress has permitted a near suppression of competing recombination mechanisms, both in the bulk of the silicon crystal and at the surfaces. This, coupled with advanced characterization techniques, has led to an improved determination of the Auger recombination rate, which is lower than previously thought. In this contribution we present a systematic study of the injection-dependent carrier recombination for a broad range of dopant concentrations of high-purity n-type and p-type silicon wafers passivated with state-of-the-art dielectric layers of aluminum oxide or silicon nitride. Based on these measurements, we develop a general parametrization for intrinsic recombination in crystalline silicon at 300 K consistent with the theory of Coulomb-enhanced Auger and radiative recombination. Based on this improved description we are able to analyze physical aspects of the Auger recombination mechanism such as the Coulomb enhancement. © 2012 American Physical Society.

Ehrmann N.,Institute for Solar Energy Research Hamelin | Reineke-Koch R.,Institute for Solar Energy Research Hamelin
Thin Solid Films | Year: 2010

We characterize sputter-deposited aluminum-doped zinc oxide (ZnO:Al) thin films on glass and silicon substrates by variable-angle spectroscopic ellipsometry in the spectral range of 240 nm to 1700 nm. The model dielectric function includes the excitonic effects of direct band-gap semiconductors in the presence of high carrier densities as well as the scattering of free carriers by ionized donors. We show that an energy-dependent broadening term of the band-gap model avoids an extended absorption tail below the absorption threshold as it usually results from Lorentzian broadening. Uniaxial anisotropy takes account of the oriented growth of hexagonal crystalline ZnO:Al thin films. All the parameters derived from the optical measurements such as surface roughness, free-carrier concentration and mobility agree with the results of independent thin-film characterization methods such as atomic-force microscopy, Hall and four-point probe measurements. In the case of the glass samples, we need an additional interface layer which is confirmed by transmission-electron microscopy as an intermix layer of ZnO and glass. © 2010 Elsevier B.V. All rights reserved.

Ehrmann N.,Institute for Solar Energy Research Hamelin | Reineke-Koch R.,Institute for Solar Energy Research Hamelin
Thin Solid Films | Year: 2012

In order to increase the efficiency of solar-thermal flat-plate collectors at temperatures above 100 °C or with low solar irradiation, we implement a double glazing with a low-emitting (low-e) coating on the inner pane to improve the insulation of the transparent cover. Since commercially available low-e glazing provides only insufficient solar transmittance for the application in thermal flat-plate collectors we are developing a sputter-deposited low e-coating system based on transparent conductive oxides which provides a high solar transmittance of 85% due to additional antireflective coatings and the use of low-iron glass substrates. Durability tests of the developed coating system show that our low e-coating system is well suitable even at high temperatures, humidity and condensation. © 2011 Elsevier B.V. All rights reserved.

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