We explore the possibility of utilizing low energy γ -photon radiation from single or multiple radioactive sources, for the production of electron-hole pairs in the semiconductors of photovoltaic cells. Our aim is to produce and store electric energy using this mechanism. The radioactive sources in the GRPVC (gamma ray photovoltaic cell) can be either naturally occurring or manufactured nuclear isomers. The γ -photon intensity can be controlled, hence the output and efficiency can also be controlled. A spherical GRPVC of 40 cm diameter, with the nuclear isomer Th * -229 (E γ = 3.5 eV, T 1/2 = 45 h) can produce a maximum open circuit voltage V ocmax = 2.626 V, at maximum efficiency η max = 52.2% initially, which occurs when the semiconductor energy gap, E g , equals the γ -photon energy, E γ . This reduces to the lower value V oc = 0.5 V at η = 12% after 188 days. The ultimate efficiency for the GRPVC studied here is about 70%, which occurs for E g = E γ ∼ 10 eV, and is above 40% for E g = E γ (with E γ 3 eV). It is also shown that nuclear isomers with long half-life can keep the GRPVC operating at high V oc and high efficiency levels for many decades, and even for centuries.
This paper reports a theoretical study of heterojunction solar cell efficiencies to include the effect of band-band impact ionization, the band-band Auger recombination and the p-n junction structure. We also study conditions under which configuration A (light encounters the large energy gap first) or configuration B (light encounters the small energy gap first) is the optimal heterojunction configuration for a solar cell, other conditions being kept fixed. Constant efficiency contour diagrams having the energy gaps as axes show that, subject to our assumptions, the best efficiencies are only of order 38% for a black body equivalent to one sun. The higher efficiencies are favoured by the smaller semiconductor widths. Open-circuit voltage, short-circuit current density and fill factor are also calculated for several sets of cell parameters.
We present calculations of efficiency, η, and open circuit voltage,
V
oc, of gamma ray photovoltaic cell (GRPVCs), in which impact ionization
processes initiated by electrons in the conduction band (C-B) are taken into account.
The contributions made to η and V
oc by multiple e–h-pair production, caused by high energy γ-photons, are
incorporated by summing up all possible higher order processes for given γ-photon
energy. The discussion is divided into two types of impact ionization: (i) in type-I,
pair creation by γ-photons and by subsequent photons due to electron impact are
treated on an equal footing; (ii) in type-II the probability for impact ionization by
electrons is a function of the γ-photon energy, and the latter is subject to
constraints set by the energy threshold parameter Θe. We find that for a
GRPVC energy gap E
g = 3.5 eV, and single e–h pair creation probability P
e–h =0.8, driven by Th-229m1(E
γ = variable, T
1/2 = 45 h)-like nuclear isomers, V
oc reaches the maximum V
ocmax = 2.7 V at ηmax ≈ 95% when E
γ = 25 eV. In type-II processes the higher orders of e–h production do not
make as high a contribution to η and V
oc because of higher energy losses. Output power is also calculated for
both types of processes and comparisons are made.
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