Marco Ernst

Dislocations in laser-doped silicon detected by micro-photoluminescence spectroscopy

We report the detection of laser-induced damage in laser-doped layers at the surface of crystalline silicon wafers, via micron-scale photoluminescence spectroscopy. The properties of the sub-band-gap emission from the induced defects are found to match the emission characteristics of dislocations. Courtesy of the high spatial resolution of the micro-photoluminescence spectroscopy technique, micron-scale variations in the extent of damage at the edge of the laser-doped region can be detected, providing a powerful tool to study and optimize laser-doping processes for silicon photovoltaics.

Macroporous Silicon Solar Cells With an Epitaxial Emitter

In this paper, we separate a macroporous silicon absorber from a monocrystalline n-type silicon wafer by means of electrochemical etching. The porosity is (31 ± 3)%. The epitaxial growth of a p ⁺-type Si layer onto one side of the macroporous silicon substrate forms a pn-junction that covers the full outer and inner surface of the macroporous layer. Epitaxy reduces the porosity to (19 ± 2)%. The thickness of the epitaxial layer is (3.0 ± 0.2) μm on the rear side and (0.4 ± 0.1) μm on the pore walls. We process (35 ± 2)-μm-thick macroporous silicon solar cells with an aperture area of 2.25 cm². The short-circuit current density is 37.1 mA cm^-2, and the open-circuit voltage is 544 mV. A fill factor of 65.1% limits the energy-conversion efficiency to 13.1%.

Demonstration of c-Si Solar Cells With Gallium Oxide Surface Passivation and Laser-Doped Gallium p + Regions

Gallium oxide (Ga₂O₃) deposited by plasma enhanced atomic layer deposition (PEALD) is shown to passivate crystalline silicon surfaces via a combination of a high negative charge and a reduction in the density of surface defects to below 1×10¹¹ cm^-2 eV^-1 at midgap. The passivation, as determined by the injection dependent excess carrier lifetime, is demonstrated to be commensurate to that of PEALD aluminium oxide (Al₂O₃). In addition, Ga₂O₃ is used as a gallium source in a laser doping process, resulting in an efficiency of 19.2% and an open circuit voltage of 658 mV in a partial rear contact p-type cell design. As such, we demonstrate that Ga₂O₃ is comparable to Al₂O₃ in terms of performance and utility, with potential material advantages over Al₂O₃.

Large area macroporous silicon layers for monocrystalline thin-film solar cells

We produce uniform macroporous double-layers on 6 inch n-type silicon substrates by electrochemical etching under rear side illumination in a hydrofluoric acid (HF)-based electrolyte. The etched area is circular with a diameter of 13 cm. We demonstrate the detachment of 20 µm thick free-standing macroporous silicon layers with an area of 8 × 8 cm2.

Macroporous silicon as an absorber for thin heterojunction solar cells

Meso- and macroporous silicon is widely studied for several applications in photovoltaic devices. We investigate macroporous silicon as an absorber for thin-film silicon solar cells. Here we review the progress of our work. We demonstrate the separation of 85 × 85 mm2-sized macroporous silicon layer from a monocrystalline n-type Cz silicon wafer. The measured optical absorption of a 26 μm thick macroporous silicon layer allows for a short-circuit current density of 37.6 mA cm-2. We measure an effective carrier lifetime of up to (38.8 ± 3.9) μs for (33 ± 2) μm thick surface passivated macroporous silicon layer. We use an analytical model to determine average surface recombination velocity S= (10 ± 2) cm s-1 for the MacPSi layer. We prepare macroporous silicon heterojunction solar cells with an energy-conversion efficiency of 7.2 %.

Efficiency Potential of P-Type Al 2 O 3 /SiN

Technological restrictions on the screen-printed rear-contact feature size on the order of 100 μm are among the limiting factors of the efficiency of p-type passivated emitter rear-contact (PERC) solar cells. Simultaneous contact opening and doping using localized laser processing can overcome these design limitations. We use 3-D numerical device simulations to show that an efficiency gain of 0.3%abs compared with a screen-printed baseline cell, is possible if laser-formed point contacts of 5 μm in size with a contact recombination parameter of 5000 fA·cm^-2 and a contact resistance of 10^-4 Ω·cm² are used. We experimentally demonstrate the implementation of simultaneous rear-surface contact opening and doping on large-area 156 × 156 mm²-sized PERC solar cells using ultraviolet (UV) and green laser systems. We achieve efficiencies of up to 19.9% for this process with a 10-nm atomic layer deposited Al₂O₃/80-nm plasma-enhanced chemical vapor deposited SiN_x rear-surface dielectric stack.

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PV cell and module manufactures optimise their products according to standard test conditions. The key parameter for financing of a solar farm is yield under field or realistic conditions. Field testing modules is expensive and time consuming. Hence we develop a methodology for simulating PV module yield based on the optical, thermal and electrical properties of the components and their stack ands layout. With our procedure we will model optical, thermal and electrical losses under realistic conditions for standard, half cell and encapsulant free modules in different locations. For now we quantify the losses for a standard module installed in Melbourne on a cloudy day. The largest loss factor is electrical, as the module voltage decreases with low irradiance.

Passivated PERC Solar Cells With Locally Laser-Doped Rear Contacts

Thin crystalline Si films (<;100 μm) are used in many applications, such as sensors, photovoltaic absorbers, and optical and particle filters. Such thin crystalline Si films are difficult to handle and break easily under standard semiconductor processing. This paper presents a laser-welding process for the mechanical connection of a thin Si film with a separate stabilizing frame that is also made of crystalline Si. We measure the tear-off stresses to be in the range of 17-50 kPa. The supported thin Si films withstand typical semiconductor processes such as plasma deposition, oxidation, and wet chemical cleaning.

Location specific PV yield and loss simulation based on module stack and layout

This paper experimentally quantifies the degree of Lambertian light trapping in thin macroporous silicon layers. The optical absorption of a 35 µm-thick macroporous silicon sample yields a fraction of 98.5 % of Lambertian light trapping.

Laser Welding for Processing of Thin Crystalline Si Wafers

Black silicon (bSi) surfaces can be effectively passivated by thermal ALD. The nanosturcures with aspect ratios up to 10 show excellent anti-reflection and light-trapping properties with absorption in the visible spectrum of over 97%. Article not available.