Julien Bailat

In situ silicon oxide based intermediate reflector for thin-film silicon micromorph solar cells

We show that SiO-based intermediate reflectors (SOIRs) can be fabricated in the same reactor and with the same process gases as used for thin-film silicon solar cells. By varying input gas ratios, SOIR layers with a wide range of optical and electrical properties are obtained. The influence of the SOIR thickness in the micromorph cell is studied and current gain and losses are discussed. Initial micromorph cell efficiency of 12.2% (Voc=1.40V, fill factor=71.9%, and Jsc=12.1mA∕cm2) is achieved with top cell, SOIR, and bottom cell thicknesses of 270, 95, and 1800nm, respectively.

High Rate Growth of Microcrystalline Silicon by VHF-GD at High Pressure

Microcrystalline silicon growth using very high frequency-glow discharge PECVD has been studied under conditions of high pressure and high VHF-power conditions. Hereby, the influence of the total gas flow and the silane concentration on the deposition rate has been investigated. Deposition rates of over 25 A/s have been achieved at relatively low total gas flows of 100 sccm. These high-rate films show device-grade quality with respect to subband gap absorption and microcrystalline structure. Dark conductivity measurements reveal midgap character and transmission electron microscopy investigations confirm a highly crystalline microstructure from the bottom to the top of the μc-Si:H films. These high-rate μc-Si:H layers are very interesting candidates for solar cell and other devices.

Microstructure and open-circuit voltage of n−i−p microcrystalline silicon solar cells

A series of microcrystalline silicon n−i−p solar cells has been deposited by very high frequency plasma enhanced chemical vapor deposition at various values of silane to hydrogen source gas ratio and on two different substrate types. Relationships between microstructure and electrical characteristics of these solar cells are investigated by transmission electron microscopy, atomic force microscopy, and I(V) measurements. A mixed phase (so-called heterophase) layer consisting of amorphous plus microcrystalline material is observed at the bottom of the solar cell and identified here as one of the key microstructural features of the device: the relationship between the crystalline nuclei density and the heterophase layer thickness is presented as well as its relationship with the open-circuit voltage (Voc). The effects of substrate roughness and of silane to hydrogen gas ratio used for the fabrication of the device on the heterophase layer are evidenced. These observations underline the importance of the fir...

Laser-Scribing Patterning for the Production of Organometallic Halide Perovskite Solar Modules

Efficiencies of solar cells based on organometallic halide perovskite absorber material have dramatically increased over the past few years. Most of efficiencies reported so far have, however, been obtained on solar cells with very small lab-scale area of less than 0.3 cm2. Only a handful of studies addressed the performances of minimodules based on perovskite, and all of them showed relatively large dead areas between the solar cell segments. In this study, we used laser-scribing techniques to pattern the module segment, reduce the dead area, and optimize the aperture area efficiency. The fraction of the dead area in the module is less than 16%, which proves that the laser-scribing technology can be adopted for monolithic serial interconnected perovskite modules and paves the way to improving module efficiency.

Limiting factors in the fabrication of microcrystalline silicon solar cells and microcrystalline/amorphous (‘micromorph’) tandems

This contribution presents the status of amorphous and microcrystalline silicon solar cells on glass, and discusses some material/fabrication factors that presently limit their conversion efficiency. Particular attention is focused on recent results and developments at the Institute of Microtechnology (IMT) in Neuchâtel. The performances and stability of microcrystalline silicon single-junction and amorphous/microcrystalline (‘micromorph’) tandem solar cells are discussed, as a function of material properties. Recent results on the electrical effect of cracks in microcrystalline silicon material are presented. Degradation under the effect of illumination is a well-known limiting factor for amorphous silicon solar cells. As a comparison, studies on the stability of microcrystalline silicon with respect to light-induced degradation are commented upon. The importance of transparent contacts and anti-reflection layers for achieving low electrical and optical losses is discussed. Finally, efforts towards industrialization of micromorph tandem solar cells are highlighted, specifically (i) the development and implementation of an in situ intermediate reflector in a large-area industrial deposition system, and (ii) recent achievements in increasing the growth rate of microcrystalline silicon.

Micromorph Solar Cell Optimization using a ZnO Layer as Intermediate Reflector

The insertion of a zinc oxide (ZnO) intermediate reflector (ZIR) between the top and bottom cell of a superstrate (p-i-n/p-i-n) micromorph tandem solar cell is analyzed, experimentally and by numerical simulation. Solar cells are deposited onto glass plates coated by surface-textured ZnO layers deposited by low-pressure chemical vapour deposition (LP-CVD). The gain in the top cell short-circuit current density (Jsc) obtained by ZIR insertion as well as the corresponding loss for the bottom cell are experimentally observed, for different values of ZIR thickness d. The gain and the loss depend nearly linearly on ZIR thickness for d < 100 nm, the maximum gain is almost 3 mA/cm2. Experimental results are compared with an optical simulation. In the latter a three-layer effective media approximation is used for modeling of thin ZIR layers. Micromorph tandem solar cells were deposited on 2 different types of front LP-CVD ZnO layers: (a) a layer optimized for a-Si:H single-junction solar cells; (b) ZnO layers specially developed for muc-Si:H cells and having undergone a novel surface treatment. In case (a) Jsc=12.1 mA/cm2 and initial conversion efficiency is 11.6 %; in case (b) Jsc=12.8 mA/cm2 and initial conversion efficiency is 11.8 %. The open-circuit voltage (Voc) value could be improved from 1.32 V to 1.41 V with an increased surface treatment time

Light-induced degradation of thin film amorphous and microcrystalline silicon solar cells

Absorption spectra of two dilution series of microcrystalline solar cells deposited by VHF-PECVD were measured by FTPS. The dilution series were composed of pin and of nip cells, with i-layers ranging from highly crystalline to mainly amorphous. This paper evaluates stability of the cells when exposed to white light (AM 1.5-like spectrum). Defect-related absorption is minimum for cells of medium crystallinity (deposited in the transition region); but is increased for theses cells by a factor 2 to 4 under light-soaking. It still remains lower than that of highly crystalline cells which show very little degradation. Variation of electrical parameters is also investigated as a function of light soaking and annealing steps. Cells of medium crystallinity show approximately 10% reversible relative efficiency loss after 1000 hours of light soaking.

When PV modules are becoming real building elements: White solar module, a revolution for BIPV

CSEM in its photovoltaic activity has developed white solar modules with conversion efficiencies above 10%. This innovative PV technology is particularly attractive to be used in building industry where PV elements can blend into building skin and become virtually hidden energy sources. The new Swiss company called Solaxess is now working on the industrialization of this new technology and the first products are expected to be in the market at the end of 2015.

Ultra-Light Amorphous Silicon Cell for Space Applications

For space applications, solar cells should be optimized for highest power density rather than for highest efficiency. In this context, relatively low efficiency thin-film solar cell may well surpass multi-junction III-V based solar cells if they can be made thin enough. In thin-film solar cells the power density is mostly limited by the substrate. The introduction of ultra-thin polymeric substrates is the key for decreasing the cell mass. In this work, a very thin polyimide film LaRCtrade-CP1 was used as substrate or superstrate for amorphous silicon solar cell fabrication. CP1 films were either fixed on a glass carrier or spin coated onto a glass carrier coated with a release agent. By depositing amorphous silicon cells on 6 mum thick CP1 films, a power density of 2.9 W/g under AM1.5g and of 3.9 W/g (estimated) under AM0 illumination spectra was achieved, in substrate (n-i-p) configuration (for a cell area of ca. 0.25 cm2). A similar cell deposited in superstate (p-i-n) configuration exhibits a record power density of 3.2 W/g under AM1.5g and an estimated value of 4.3 W/g under AM0 illumination spectra. Release of the finished solar cells from the glass carrier was also tested

Improved interface between front TCO and microcrystalline silicon p-i-n solar cells.

Note: IMT-NE Number: 335 Reference PV-LAB-CONF-2001-002 Record created on 2009-02-10, modified on 2017-05-10