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Eggleston B.,Suntech RandD Australia Pty Ltd | Eggleston B.,University of New South Wales | Varlamov S.,University of New South Wales | Green M.,University of New South Wales
IEEE Transactions on Electron Devices | Year: 2012

A new process was presented to anneal crystallographic defects in solid-phase crystallized silicon that produces higher Suns-V oc voltages than the conventional belt-furnace annealing (BFA) process. A few-millisecond continuous-wave diode laser treatment anneals defects present in the polycrystalline silicon and activates dopants. It is shown that the silicon/glass-interface system reaches an effective steady state at every point during the laser treatment, and the relative temperature profile is determined by the laser beam profile rather than its power or scanning speed. The peak temperature that is reached during a few-millisecond laser exposure is shown to increase and then level off with laser dose, indicating partial recrystallization of the film. A reduction in boron-doped p-type sheet resistance and phosphorus-doped emitter resistance is reported for a wide range of laser dose and scanning speed. The highest substrate temperature required during the process sequence is reduced from 960 °C to 620 °C. A peak 1-sun voltage of 492 mV is achieved using a 4-ms exposure at 500-J · cm -2 laser dose, which is an improvement of 32 mV over the voltage after optimized BFA. © 2012 IEEE.

Chowdhury A.,French National Center for Scientific Research | Schneider J.,CSG Solar AG | Schneider J.,Fraunhofer Center for Silicon Photovoltaics | Dore J.,CSG Solar AG | And 3 more authors.
Applied Physics A: Materials Science and Processing | Year: 2012

Thin film polycrystalline silicon films grown on glass substrate were irradiated with an infrared continuous wave laser for defects annealing and/or dopants activation. The samples were uniformly scanned using an attachment with the laser system. Substrate temperature, scan speed and laser power were varied to find suitable laser annealing conditions. The Raman spectroscopy and Suns-V ∞c analysis were carried out to qualify the films quality after laser annealing. A maximum enhancement of the open circuit voltage V ∞c of about 100 mV is obtained after laser annealing of as-grown polysilicon structures. A strong correlation was found between the full width half maximum of the Si crystalline peak and V ∞c. It is interpreted as due to defects annealing as well as to dopants activation in the absorbing silicon layer. The maximum V ∞c reached is 485 mV after laser treatment and plasma hydrogenation, thanks to defects passivation. © 2012 Springer-Verlag.

Dore J.,University of New South Wales | Dore J.,Suntech RandD Australia Pty Ltd | Varlamov S.,University of New South Wales | Green M.A.,University of New South Wales
IEEE Journal of Photovoltaics | Year: 2015

The intermediate layer (IL) between the glass and silicon plays an important role in laser-crystallized thin-film silicon solar cells. {\rm SiO}-x, {\rm SiN}-x, and {\rm SiC}-x deposited by RF sputtering or plasma-enhanced chemical vapor deposition, either as single layers or in stacks, have been tested as ILs with regard to silicon wettability and silicon crystal quality and the effect of hydrogen passivation. {\rm SiC}-x is the best wetting layer, allowing a larger laser crystallization process window than {\rm SiO}-x or {\rm SiN}-x. {\rm SiN}-x layers are limited by pinholing, which increases in severity with laser fluence. {\rm SiO}-x ILs result in lower silicon grain-boundary density compared with {\rm SiC}-x-based layers and to {\rm SiN}-x-based layers. Hydrogen passivation of laser-crystallized silicon on single layer {\rm SiO}-x has no impact on V-{{\rm OC}} , while an improvement of around 60 mV is found for samples on {\rm SiO}-x/{\rm SiN}-x/{\rm SiO}-x stacks. Diffusion of dopants from the IL are found to create a uniformly doped absorber with no evidence of a front-surface field. © 2011-2012 IEEE.

Qiu Y.,IMEC | Qiu Y.,CAS Shanghai Institute of Microsystem and Information Technology | Kunz O.,Suntech RandD Australia Pty Ltd | Fejfar A.,ASCR Institute of Physics Prague | And 6 more authors.
Solar Energy Materials and Solar Cells | Year: 2014

The hydrogen plasma passivation of thin film polycrystalline silicon (pc-Si) was investigated in conjunction with plasma texturing process to make efficient heterojunction solar cells. The pc-Si layers were first treated using direct and remote hydrogen plasma technologies. The heterojunction solar cells were then fabricated by subsequent deposition of i/n+ a-Si:H. Hydrogenation at high temperature (610 C) results in enhanced dissolution and diffusion of hydrogen in pc-Si by a factor of about 3 and 4, respectively, in comparison with those at low temperature (420 C). The hydrogen atoms in the pc-Si layer mainly bond to the silicon dangling bonds and form complexes with dopant atoms. In addition, platelets defects are generated by the hydrogen plasma in the sub-surface region of pc-Si hydrogenated at 420 C and cause higher saturation current in the space charge region whilst they form in the region deeper than 1 μm at 610 C. Removal of the platelets using SF 6/N2O plasma post-texturing after low-temperature hydrogenation not only enhances the short circuit current but also improves the open circuit voltage and the fill factor simultaneously. Combining plasma pre-texturing with high-temperature hydrogenation, the best 2 μm-thick pc-Si heterojunction solar cell reaches an efficiency of 8.54%. © 2013 Elsevier Ltd. All rights reserved.

Steffens S.,Helmholtz Center Berlin | Becker C.,Helmholtz Center Berlin | Zollondz J.-H.,CSG Solar AG | Chowdhury A.,LInstitut dElectronique du Solide et des Systemes | And 5 more authors.
Materials Science and Engineering B: Solid-State Materials for Advanced Technology | Year: 2013

A variety of defect healing methods was analyzed for optimization of polycrystalline silicon (poly-Si) thin-film solar cells on glass. The films were fabricated by solid phase crystallization of amorphous silicon deposited either by plasma enhanced chemical vapor deposition (PECVD) or by electron-beam evaporation (EBE). Three different rapid thermal processing (RTP) set-ups were compared: A conventional rapid thermal annealing oven, a dual wavelength laser annealing system and a movable two sided halogen lamp oven. The two latter processes utilize focused energy input for reducing the thermal load introduced into the glass substrates and thus lead to less deformation and impurity diffusion. Analysis of the structural and electrical properties of the poly-Si thin films was performed by Suns-VOC measurements and Raman spectroscopy. 1 cm2 cells were prepared for a selection of samples and characterized by I-V-measurements. The poly-Si material quality could be extremely enhanced, resulting in increase of the open circuit voltages from about 100 mV (EBE) and 170 mV (PECVD) in the untreated case up to 480 mV after processing. © 2012 Elsevier B.V. All rights reserved.

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