Abstract:
In this project the factor of efficiency of excitonic solar cell is studied, especially band gap
energy, binding energy and the second law of thermodynamics that control the efficiency of solar
cell. Excitonic solar cells comprised of materials such as organic semiconductors, inorganic
colloidal quantum dots, and carbon nanotubes, are fundamentally different than crystalline,
inorganic solar cells in that photo generation of free charge occurs through intermediate, bound
exciton states. Here, I reviewed that the second law of thermodynamics limits the maximum
efficiency of excitonic solar cells below the maximum of 31% established by Shockley and
Queisser 1961 for inorganic solar cells (whose exciton-binding energy is small). In the case of
ideal heterojunction excitonic cells, the free energy for charge transfer at the interface, G, places
an additional constraint on the limiting efficiency due to a fundamental increase in the
recombination rate. In a thermodynamic treatment electromagnetic radiation of any kind is
described. The radiation is accounted by introducing the chemical potential of photons. Instead
of an effective temperature all kinds of radiation have the real temperature of the emitting
material. As a result Planck’s law for thermal radiation is extended to radiation of any kind. The
concept of the chemical potential of radiation is discussed in detail in conjunction with lightemitting semiconductor, two-level systems, and lasers. It allows the calculation of absorption
coefficients of emission spectra of luminescent materials, and of radiative recombination
lifetimes of electrons and holes in semiconductors. This review is used to calculate the Fill
Factor (FF) and the power conversion efficiency (η) of the device can be indicated by using
maximum power. At open circuit condition electron-hole pairs are continually created as a result
of the photon flux absorption, the mechanism to counter balance this non-equilibrium condition
is recombination.
