Harvesting Betavoltaic and Photovoltaic Energy with Three Dimensional Porous Silicon Diodes

Conventional two-dimensional p-n diodes can be used for betavoltaic and photovoltaic energy conversion, but the device efficiency is limited by the planar geometry. We propose and demonstrate a novel three-dimensional diode geometry based on porous silicon. The 3D pore array provides two very important features: (1) the storage of the radioisotope energy source and (2) its extreme proximity to the p-n junction on each pore wall. The particle energy losses are thereby minimized prior to entering the conversion layer. In betavoltaics, our 3D betavoltaic device efficiency is 10 times that of a similar planar device. In photovoltaics, photons play the role of beta particles and photon trapping inside the pores enhances the conversion efficiency. Further fabrication and geometry optimization can result in practical, high performance devices.