Abstract:
Today’s research works surrounding Solar cells revolve around finding out different ways to
improve efficiency. Open Circuit Voltage is now considered as an important parameter in
determining efficiency of Solar Cell. In this work, analytical modeling of open circuit voltage
(VOC) is performed for Schottky Barrier (SB) Solar Cell and mathematical expression for VOC
is derived for all levels of injection of carriers. No analytical work for finding open circuit
voltage of SB solar cell for all levels of injection has been done previously. Some of the
works attribute to analytical modeling of open circuit voltage of SB Solar Cell for special
cases of low and high level of injection. This work is valid for all levels of injection and it has
tracked down the previous results for low and high level of injection by applying necessary
assumptions. Mathematical expressions obtained after applying necessary assumptions are
then compared with previous mathematical modeling of low and high level of injection.
Mathematical expression of VOC for low and high level of injection is found same to those
obtained by works done previously. For finding out this mathematical representation of open
circuit voltage second order differential equation is required to be solved to obtain excess
minority carrier hole concentration in depletion and neutral region of a n-type SB Solar Cell.
Proper boundary conditions are applied in evaluating constants of the solution of the
differential equation. Effect of doping concentration, Metal work function, effective surface
recombination velocity at the n-n+ interface and thickness of semiconductor on VOC has been
studied. Variation of VOC with doping concentration and metal work function has been
explained. Both Si and GaAs are considered as semiconductors and different metals are used.
Comparison of VOC for different levels of injection as function of doping concentration has
been performed. With the increase of doping concentration and metal work functions VOC
increases for different levels of injection. For changing level of injection from low to all level
it has been found that Voc increases by around 0.1 volt for a certain metal and while
changing level of injection from all level to high level around 0.1 volt increase of VOC occurs
for a certain metal. While changing doping level from 1014 to 1017 range, Voc increases about
0.1-0.25 volt for various metal combinations. Using GaAs instead of Si means increase of
about 0.2 volt in VOC. Increase of metal work function indicates increase in VOC. The
variation of VOC is less prominent among various levels of injection while using n-GaAs
instead of n-Si as semiconductor. Increase of effective surface recombination velocity Seff and
thickness of the semiconductor L does not imply significant change in VOC. With increase of
Seff, VOC decreases slightly for all level and low level of injection. With increase of L, VOC
remains almost constant under all level and low level of injection. High level of injection
indicates slight increase of VOC with Seff and L. In the end comparisons of low level and high
level of injection has been performed while using current analytic model with the previous
result obtained for low and high level of injection.
