Sliver Cells in Thermophotovoltiac Systems

Thermophotovoltaic systems are direct conversion heat engines that use photovoltaic cells to generate electricity from the light radiated by a heated object. Sources of heat for thermophotovoltaic (TPV) systems include sunlight, the combustion of fossil fuels, radioactive decay and industrial waste heat. Previous modelling indicated that thin cells, thinner than 100μm, are optimal for use in TPV systems. Sliver cells are a novel type of photovoltaic cell fabricated from single crystal semiconductor wafers. They are bifacial, narrow, have metal contacts at the edges of the cell, and are very thin - of the order of tens of micrometers. A computational model was constructed to examine and compare the performance of sliver cells with state-of-the-art conventional back-contact cells. Silicon was modelled as the semiconductor material due to the availability of modelling data and to provide an indication of the feasibility of thin silicon cells in TPV systems. The analysis of silicon TPV cells was extrapolated to gallium antimonide.

Within the range of parameters investigated, it was found that sliver cells do not offer a clear advantage over well-designed conventional cells in TPV systems. This was observed to be a result of horizontal carrier transport resistances across sliver cell widths, which were limited in this study to 300μm. Optimal cells for thermophotovoltaic systems were found to be thin back-contact cells with spectral filtering that reflects high-energy photons back to the emitter. Practical considerations such as heat-sinking and cell-module circuitry were found to favour sliver cell geometries. Silicon cells were observed to perform well at emitter temperatures that are above the current range of feasibility for TPV systems. Recommendations are made for the design of future TPV systems, potential fabrication processes for the manufacturing of optimal TPV cells are outlined, and the properties of future wholesystem thermophotovoltaic models are discussed.

Keywords: thermophotovoltaics, sliver cells, photovoltaic modelling