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Betavoltaic energy converters (i.e., β-batteries) are attractive power sources because of their potential for high energy densities (>200 MWh/kg) and long duration continuous discharge (>1 year). However, conversion efficiencies have been historically low (<3%). High efficiency devices can be achieved by matching β-radiation transport length scales with the device physics length scales. In this work, the efficiency of c-Si devices using high-energy (>1 MeV) electrons emitted from 90Sr as a power source is investigated. We propose a design for a >10% efficient betavoltaic device, which generates 1 W of power. A Varian Clinac iX is used to simulate the high-energy electrons emitted from 90Sr, and a high efficiency c-Si photovoltaic cell is used as the converter. The measured conversion efficiency is 16%. This relatively high value is attributed to proper length scale matching and the generation of secondary electrons in c-Si by the primary β-particles.

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h i g h l i g h t sAn iris mechanism proposed in response to fluctuations in solar energy. Iris motion controlled with the use of Nickel-Titanium Shape Memory Alloy springs. Variation of the force exerted by SMA spring w.r.t. temperature tested experimentally. An analytical expression that relates the aperture area and crank rotation is given. SMA springs showed promising actuation mechanism as a replacement to motor.

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