Alpha-Photovoltaics for Milliwatt Applications

Abstract

Isotope power sources can serve applications for sensor or communication nodes that are required to last the lifetime of infrastructure because they possess at least 1000 times higher energy density, long operational lifetimes (> 10 years), and wider operational temperature range compared to chemical power sources. There are different methods of converting radiation energy into electrical energy at low power (nW – mW) levels, the most prevalent is betavoltaic devices which convert beta particles energy directly into electrical energy using a semiconductor junction. However, the current state-of-the art betavoltaics can only produce 10’s of micro-watts/cm2, and are not suitable for applications requiring mW output power. Alpha particle emitting isotopes have higher energies than beta isotopes and can be used to produce power in mW range, but require radiation tolerant ultra-wide-bandgap semiconductor junctions, which are not widely available yet. Therefore, it is necessary to look at alternate approaches to harvest energy from alpha decay using existing semiconductor technology. In this paper, we have validated one such approach to convert alpha particles energy into electrical energy by employing an intermediate phosphor layer placed between an alpha source and an InGaP PV cell. We simulated the average energy emission of Am-241 using a pelletron source accelerating He2+ ions and exposed the InGaP PV with phosphor film deposited on top while measuring the IV characteristics throughout the experiment. We measured an output power of 165 μW/cm2 at 4.5 MeV beam, representing a fluence of 3.75 × 1013 ions.