The production of crystalline silicon thin-film solar cells on cost effective ceramic substrates depends on a highly reliable diffusion barrier to separate the light absorbing layers from the substrate. Ideally this intermediate layer should be deposited with cost effective techniques, be conductive and should feature optical confinement. Furthermore the intermediate layer should withstand high temperatures and harsh chemical environments like they occur during solar cell processing. Especially stability against oxidizing solvents like HNO3 or inactivity during e.g., oxide removing steps with HF is required. Crystalline silicon carbide (c-SiC) deposited by atmospheric pressure chemical vapour deposition (APCVD) can match all those requirements and additionally fits the thermal properties of crystalline silicon. The c-SiC intermediate layer is deposited from methyltrichlorosilane (MTS) and H2 at 1100 degrees C. Under these conditions, growth of solely cubic 3C-SiC could be observed by X-ray diffraction measurements. Use of such intermediate layers during high temperature steps prevents diffusion of transition metals, originating from the substrates, into active silicon layers. Doping of these 3C-SiC layers with nitrogen results in specific resistivity of less than 100 ohms cm. The different potentially cost-effective substrates are made from graphite, crystalline silicon, sintered silicon carbide and sintered zircon (ZrSiO4). Surface properties of the coated substrates were investigated, explaining changes in surface roughness and influences on the solar cell processing.

Monolithic tandem cells involving a top cell with Si nanocrystals embedded in SiC (Si NC/SiC) and a c-Si bottom cell have been prepared. Scanning electron microscopy shows that the intended cell architecture is achieved and that it survives the 1100 °C anneal required to form Si NCs. The cells exhibit mean open-circuit voltages Voc of 900–950 mV, demonstrating tandem cell functionality, with ≤580 mV arising from the c-Si bottom cell and ≥320 mV arising from the Si NC/SiC top cell. The cells are successfully connected using a SiC/Si tunnelling recombination junction that results in very little voltage loss. The short-circuit current densities jsc are, at 0.8–0.9 mAcm−2, rather low and found to be limited by current collection in the top cell. However, equivalent circuit simulations demonstrate that in current-mismatched tandem cells such as the ones studied here, higher jsc, when accompanied by decreased Voc, can arise from shunts or breakdown in the limiting cell rather than improved current collection from the limiting cell. This indicates that Voc is a better optimisation parameter than jsc for tandem cells where the limiting cell exhibits poor junction characteristics. The high-temperature-stable cell architecture developed in this work, coupled with simulations highlighting potential pitfalls in tandem cell analysis, provides a suitable route for optimisation of Si NC layers for photovoltaics on a tandem cell device level

This work describes the processing of recrystallized silicon thin-film solar cells and its typical defects. Zircon (ZrSiO4) ceramic substrates of technical grade with potential production costs of <; 20 €/m2 were used. Those substrates were encapsulated in crystalline silicon carbide, deposited by atmospheric pressure chemical vapor deposition (APCVD). The active silicon layers were also formed using APCVD. Zone-melting recrystallization (ZMR) was used to enlarge Si grains. Si films crystallized on SiC show characteristic \u7f3 twin grain boundaries parallel to the growth direction. The Si crystals achieve widths up to several mm and lengths of several cm. Solar cells made from such material achieved open circuit voltages up to 566 mV on zircon and up to 600 mV on equally processed mc-Si

The development of crystalline silicon thin films (cSiTF) for several solar cell concepts is pursued by various research groups. A common challenge is the electrical characterisation of silicon films with a thickness in the range of 2 to 20 μm. Since the improvement of layer quality and the optimisation of layer thickness is a critical factor, the measurement of the diffusion length respectively the minority carrier lifetime of such silicon films is a very important factor and will therefore be addressed in this paper. The solar cell structure including substrate and possibly dielectric intermediate layers is one of the major challenges for these lifetime measurements. Besides that the lifetime regime below 5 μs is another challenge for certain measurement techniques. Therefore a system for microwave photo conductance decay (MWPCD) measurements by Semilab was used in these experiments and a modified analysis algorithm was implemented. Finally, the lifetime measurements of cSiTF fabricated by epitaxial growth and by recrystallisation will be presented

No abstract