Abstract
A new class of thermophotovoltaic cells converting thermal radiation power into electrical power from sources at very high temperature (>1800 °C) is currently emerging. Like concentrating solar cells, these cells are subject to resistive losses due to high current densities. Hence, tandem cells with horizontally stacked junctions have been recently developed and have achieved record pairwise efficiencies and electrical power densities. Here, we employ alternatively a silicon vertical multijunction cell as a means of reducing current density while operating at high voltage. Both under 1-Sun illumination and that of a thermal source at 2100 °C, the cell kept at 25 °C exhibits open-circuit voltages above 25 V and short-circuit currents below 6 mA. With a series resistance below a few milliohms, Joule losses are negligible. The cell receiving 2.01 W/cm 2 and absorbing 1.24 W/cm 2 generates an electrical power density of 0.14 W/cm 2 , leading to a pairwise efficiency of only 11.4% because of substantial out-of-band absorption. With photonic engineering of the emitter ensuring no out-of-band emission, this efficiency could reach 52.9% under the same illumination conditions. The cell could also be used under bifacial conditions, which would double the electrical power. However, due to the heat generated in the cell, its temperature can exceed 25 °C. Advantageously, a moderate temperature coefficient of the electrical power of (−0.309 ± 0.005)%/ °C is measured under 1-Sun illumination and it becomes much smaller, (−0.18 ± 0.01)%/ °C, in thermophotovoltaic conditions. These results suggest reopening the path of research aimed at optimizing the design and fabrication of vertical multijunction cells for thermophotovoltaic conversion.