An implantable assembly is disclosed comprising a diode device charging assembly having the means for transferring thermal energy from a living organism to a diode device, means for creating electrical energy from said thermal energy, and means for charging an implantable device with said electrical current. The diode device of this invention is a thermotunneling or thermionic converter. In a preferred embodiment the electrodes of the diode device have been modified to reduce their work function by through the addition a periodically repeating structure comprised of one or more indentations of the dimensions so as to create de Broglie wave interference, leading to a change in electron work function. The implantable assembly utilizes a temperature difference in a body to efficiently generate energy to be harnessed by a wide range of devices.