  Thermionic energy conversion (TEC) using nano materials is an emerging field
of research. Graphene can stand high temperature as high as 4600 K in vacuum.
Its work function can be engineered from its high value (for monolayer/bilayer)
4.6 eV to 3. 7 eV, 3.8 eV, 3.5 eV and 3.4 eV, through the use of K2CO3, Li2CO3,
Rb2CO3, Cs2CO3 as shown by Kwon et al43 and to as low as 0.7 eV as shown by
Yuan et al. Such remarkable property along with good electrical conductivity,
high dielectric constant makes engineered graphene an ideal candidate to be
used as both emitter and collector in a thermionic energy converter. Since
large size parabolic trough solar concentrator is now available, there is a
great possibility of harnessing solar energy efficiently and cost effectively,
if complex functional relation of efficiency of solar energy conversion with
solar insolation, area of solar concentrator, work functions (We, Wc) &
temperatures, emissivity of emitter and collector, space charge control etc.
can be understood clearly. Using modified Richardson-Dushman equation this work
focuses on theoretical studies of these aspects, excluding the space charge
control. What is necessary for high efficiency is good combination of (We, Wc),
with a difference > 0.5 eV, proper collector temperature and high solar energy
input. Such solar energy conversion would reduce the dependence on silicon
solar panel and has great potential for future applications.
