Abstract
The sustainable development of clean and efficient electricity generation techniques accelerated the research for invention of alternative electricity generation methods. In this chapter, the conceptual analysis of newly invented photon-enhanced thermionic emission (PETE) energy conversion process has been presented. It is a promising option for harvesting solar energy in terms of capturing photon as well as thermal energy simultaneously and converting solar energy into electrical energy based on photovoltaic and thermionic emission processes of energy conversion. Thus, the PETE process utilizes photons for PV conversion and heat of radiation for thermionic emission process. The main objective of this chapter is to review and analyze the performance of PETE converters including thermal modeling, choice of materials, and parametric optimization. The appropriate choice of material requirements for cathode and anode of PETE converters is necessary for practical design of PETE converters. The PETE converter may be an efficient future option for electricity generation using solar energy.
TopNomenclature
A0: Area (m2)
NC: Effective density of states in conduction band (# per cm3)
c: Speed of light (m/s)
nid: Diode ideality factor
Eg: Energy band gap of semiconductor (eV)
NV: Effective density of states in valence band (# per cm3)
Eg,PV: Energy band gap of semiconductor material used in solar cell (eV)
NA: Electron concentration for ionized acceptor (# per cm3)
EF,p: Quasi-Fermi levels for valence band (eV)
NA: Concentration of p-type acceptor (# per cm3)
EF,n: Quasi-Fermi levels for conduction band (eV)
neq: Equilibrium electron concentration without photo-excitation (# per cm3)
EF: Equilibrium Fermi level (eV)
n: Electron concentration with photo-excitation (# per cm3)
EA: Ionization energy of p-type acceptor (eV)
δn: Excess carrier concentration from equilibrium condition (# per cm3)
EC: Conduction band minimum energy level (eV)
P: Holes concentration with photo-excitation (# per cm3)
EV: Valence band maximum energy level (eV)
peq: Equilibrium hole concentration without photo-excitation (# per cm3)
Ex: Exergy (W)
P: Power (W)
En: Energy (W)
Q: Energy (W)
G: Solar irradiation (W/m2)
R0: Rate of photon emission at equilibrium conditions (# per m2 per sec)
H: Cathode height (cm)
R: Rate of photon emission at non-equilibrium conditions (# per m2 per sec)
H: Planck constant (J-s)
Rr: Rate of photon-enhanced recombination at non-equilibrium conditions (# per m2 per sec)
I0: Reverse saturation current (A)
RC: Rate of thermionic emission in cathode (# per m2 per sec)
Irr: Irreversibilities (W)
RA: Rate of reverse thermionic emission from anode (# per m2 per sec)
Iph: Photocurrent (A)
RS: Rate of photon induced electrons (# per m2 per sec)
I: Electrical current (A)
R: Resistance (Ω)
J: Current density (A/cm2)
S: Entropy (W/K)
KRD: Richardson Dushmann constant (A/cm2K2)
sr: Aspect ratio
kB: Boltzmann constant (J/K)
T: Temperature (K)
m0: Electron mass (9.1x10-31 kg)
U: Overall heat transfer coefficient (W/m2K)
mn: Effective electron mass (kg)
V: Voltage (V)
mp: Effective hole mass (kg)
W: Width (m/cm)
Key Terms in this Chapter
Work Function: It is defined as the minimum amount of thermodynamic work or energy required to remove an electron from a solid to a point in the vacuum immediately outside the solid surface.
Mobility: It is the characteristic of an electron to move through a metal or semiconductor upon application of electric field.
Ionization Energy: It is the minimum energy required to remove an electron from the ground state of an atom.
Absorption Coefficient: It describes how far the light of a particular wavelength can penetrate into a material of a given thickness before it is absorbed by the material.
Current Density: The amount of electric current travelling per unit cross-section area is called as current density.
Electron Affinity: Electron affinity of a semiconductor is the minimum energy required to move an electron from the conduction band bottom to the vacuum level.
Radiative Recombination: When an electron from the conduction band directly combines with a hole in the valence band and releases a photon, it is called radiative recombination.
Carnot Efficiency: It describes the maximum thermal efficiency that a heat engine can achieve as permitted by the second law of thermodynamics.
Vacuum Level: It is the energy of a free electron (an electron outside the semiconductor) which is at rest with respect to the semiconductor.
Diffusion Length: It is the average distance that a carrier covers between generation and recombination.
Fermi Level: the energy level (if it exists) which has a 50% probability of getting occupied by an electron for the given temperature of the solid and at absolute zero temperature occupancy is 100%.
Energy Band Gap: It is defined as the minimum energy required to excite an electron up to a state in the conduction band where it can participate in conduction.
Photon: A photon is the quantum of electromagnetic radiation. A photon is a particle of light defined as a discrete bundle or quantum of electromagnetic radiation or light.