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31st European Photovoltaic Solar Energy Conference and Exhibition; 365-368, We describe the process for fabricating interdigitated back-contacted cells compatible with thin (40μm) monocrystalline silicon foils. Throughout the process, the foils are supported by either the silicon parent substrate, or by a host (glass) superstrate using adhesive bonding. For a number of process steps, we describe possible issues, boundary conditions and performance. Using the integrated process which is fully compatible with bonded foils, cells were fabricated on a freestanding, non-textured wafer. An efficiency of 18.0% was achieved, the main limitations being the absence of surface texturing and a non-optimized amorphous silicon emitter.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1967-1970, ITRPV roadmaps predict that the thickness of wafers will continuously decrease. For thicknesses below 100 μm, alternatives for wafer sawing need to be developed. IMEC proposes a foil creation technique by lifting off a thin epitaxially grown layer as a substitute for wafer sawing to create substrates with a thickness around 40 μm. To enable integration of those foils into solar cells, with sufficiently high yield, an ‘i2-module’ concept is proposed. This is an interdigitated back-contact solar module process that can be applied on very thin foils, and where those foils are supported by either the parent substrate or the module glass at all times. To define a process flow adapted to the requirements and limitations of the epitaxial foils, the stability of the foils is tested during a wide range of front-side processes. It is found that epitaxial foils are not sufficiently stable during high temperature processes. Therefore, a process sequence based on low-temperature processes is defined for front-side processing. The yield of each step in the front-side process flow is evaluated. The constrains for front-side processing, together with the constrains defined by the silicone bond, lead to the choice of a back-contact heterojunction (HJ) cell with a PECVD a-Si:H emitter.

29th European Photovoltaic Solar Energy Conference and Exhibition; 1024-1027, In this paper, the electrical and optical characteristics of the Indium-Doped Tin Oxide (ITO) are tuned in order to design an ITO-based spacer between the a-Si:H and the metal contact suited for Amorphous / Crystalline Heterojunction interdigitated Back Contact Solar Cells (a-Si:H / c-Si HJ i-BC). ITO carrier concentration, mobility, resistivity, extinction coefficient, and work function, as well as the ITO / a-Si:H specific contact resistances are evaluated as a function of O2 relative flow rate during ITO deposition. An ITO having carrier concentration of 4.5x1019 cm-3, mobility of 20.2 cm2/(V.s) and resistivity of 6.24 mΩ.cm is found to be an optimum leading to ITO / a-Si:H(p/i) and ITO / a-Si:H(n/i) specific contact resistances values of 0.6 Ω.cm2 and 0.1 Ω.cm2 respectively and a RS reflectance of 58% at 1200nm when integrated in Silver / ITO / a-Si:H / c-Si(textured) test structures.

28th European Photovoltaic Solar Energy Conference and Exhibition; 1351-1354, In imec's i2Module concept, rear-contacted solar cells are fabricated after bonding monocrystalline silicon foils to module glass. The specific structure of the substrate after bonding imposes a temperature budget limitation of 300°C. This presents a challenge to device integration, amongst others for emitter passivation. It is shown that state-of-the-art emitter passivation by thermal oxide can be degraded by plasma processes and metal sputtering. Hydrogenated amorphous silicon presents an alternative that is compatible with low process temperatures and is not affected by subsequent processing. J0 values of approximately 50fA/cm2 have been obtained, both on freestanding wafers and on bonded thin silicon foils.