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Bielefeld, Germany

Lukermann F.,Bielefeld University | Heinzmann U.,Bielefeld University | Stiebig H.,Bielefeld University | Stiebig H.,Malibu GmbH and Co
Applied Physics Letters | Year: 2012

By embedding silver nanoparticles (Ag NPs) of approximately 20 nm diameter inside the intrinsic layer of thin hydrogenated amorphous silicon (a-Si:H) n-i-p devices, a photocurrent is measured for photon energies below the a-Si:H bandgap. This is attributed to the excitation of charge carriers from defect states created by the incorporation of the Ag inside the silicon network. The defect location inside the strong electromagnetic fields close to the resonant absorbing NPs enables high transition rates. This is a proof of concept for the use of the impurity photovoltaic effect in a-Si:H devices. © 2012 American Institute of Physics. Source


Grant
Agency: Cordis | Branch: FP7 | Program: CP-IP | Phase: ENERGY.2011.2.1-2;NMP.2011.1.2-1 | Award Amount: 12.88M | Year: 2012

In recent years, the effort in thin-film silicon (TFSi) was made at solving industrialization issues. In 2010, several companies demonstrated 10% stable modules (> 1 m). The major bricks for efficient production are now in place. Next challenges are linked to the fact that TFSi multi-junction devices, allowing for higher efficiency, are complex devices, in which the substrate geometry and each layer have an impact on the full device. This explains why the first industrializations focused on single technology roads (e.g., Jlich-AMAT or EPFL-Oerlikon approaches). This project focuses at bringing the next-generation technology to the market, using newly developed state-of-the art knowledge to solve the complex puzzle of achieving at the same time strong light in-coupling (high current) and good electrical properties (open-circuit voltage and fill factor). In a unique collaborative effort of the leading EU industries and research institutions in the field, the consortium will go beyond the current technology status by Introducing novel materials, including multi-phase nanomaterials (such as doped nc-SiOx, high crystallinity nc-Si materials), stable top cell materials, nanoimprinted substrates and novel or adapted transparent conductive oxides; Designing and implementing ideal device structures, taking into account the full interaction of layers in multi-junction devices; Controlling the growth of active layers on textured materials; Working at processes that could allow a further extension of the technology such as very high rate nc-Si deposition or multi-step superstrate etching; Transferring processes, including static and dynamic plasma deposition, from the laboratory to pilot scale, with first trials in production lines. The targets of the project is to achieve solar cells with 14% stable efficiency, leading to the demonstration of reliable production size prototypes module at 12% level. Potential cost below 0.5/Wp should be demonstrated.


Jovanov V.,Jacobs University Bremen | Palanchoke U.,Jacobs University Bremen | Magnus P.,Malibu GmbH and Co | Stiebig H.,Malibu GmbH and Co | And 6 more authors.
Optics Express | Year: 2013

The influence of realistic interface morphologies on light trapping in amorphous silicon thin-film solar cells with periodic surface textures is studied. Realistic interface morphologies are obtained by a 3D surface coverage algorithm using the substrate morphology and layer thicknesses as input parameters. Finite difference time domain optical simulations are used to determine the absorption in the individual layers of the thin-film solar cell. The influence of realistic interface morphologies on light trapping is determined by using solar cells structures with the same front and back contact morphologies as a reference. Finally the optimal surface textures are derived. © 2013 Optical Society of America. Source


Einsele F.,Julich Research Center | Beyer W.,Julich Research Center | Beyer W.,Malibu GmbH and Co | Rau U.,Julich Research Center
Journal of Applied Physics | Year: 2012

Thermal stability of passivating layers in amorphous/crystalline silicon (a-Si/c-Si) heterojunction solar cells is crucial for industrial processing and long-term device stability. Hydrogenated amorphous silicon (a-Si:H) yields outstanding surface passivation as atomic hydrogen saturates silicon dangling bonds at the a-Si/c-Si interface. Yet, a-Si surface passivation typically starts to degrade already at annealing temperatures in the range of 200 to 250°C depending on annealing time, and optical absorption in front layers of a-Si reduces the short circuit current density. We show that oxygen incorporation into a-Si:H films enhances the thermal stability of the passivation and reduces parasitic absorption. We further show that for good passivation of the a-Si/c-Si interface, a compact material structure of the a-Si:O:H films is required where atomic hydrogen is the dominating type of diffusing hydrogen species. For plasma deposited a-Si:O:H films, oxygen incorporation of up to 10 at. %leads to an increase of the optical band gap while the hydrogen concentration is almost constant at approximately 10 at.%. For oxygen concentrations below 3, the films yield surface recombination velocities as low as 10 cm/s on p-type wafers, and the temperature stability improves by about 50 K compared to pure a-Si:H. For films with relatively low oxygen content, hydrogen effusion spectra and Fourier transform infrared spectroscopy (FTIR) indicate a compact microstructure where only atomic H diffuses. For oxygen concentrations above 3, the passivation quality reduces and H effusion and FTIR suggest the formation of an open, void-rich material where molecular H 2 diffuses. In this case, annealing above 400°C results in improved interface passivation, presumably due to a densification of the material. Likely, this densification results in an increased density of atomic H, which saturates Si dangling bonds near the c-Si interface. © 2012 American Institute of Physics. Source


Beyer W.,Malibu GmbH and Co | Beyer W.,Julich Research Center | Hilgers W.,Julich Research Center | Prunici P.,Malibu GmbH and Co | Lennartz D.,Julich Research Center
Journal of Non-Crystalline Solids | Year: 2012

Effusion measurements of hydrogen and of implanted helium are used to characterize the presence of voids in hydrogenated amorphous silicon (a-Si:H) materials as a function of substrate temperature, hydrogen content, etc. For undoped plasma-grown a-Si:H, interconnected voids are found to prevail at hydrogen concentrations exceeding 15-20 at.%, while isolated voids which act as helium traps appear at hydrogen concentrations ≤ 15 at.%. The concentration of such isolated voids is estimated to some 10 18/cm 3 for device-grade undoped a-Si:H deposited at a substrate temperature near 200 °C. Higher values are found for, e.g.; doped material, hot wire grown a-Si:H and hydrogen-implanted crystalline Si. The results do not support recent suggestions of predominant incorporation of hydrogen in a-Si:H in (crystalline silicon type) divacancies, since such models predict a concentration of voids (which act as helium traps) in the range of 10 21/cm 3 and a correlation between void and hydrogen concentrations which is not observed. © 2011 Elsevier B.V. Source

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