Researcher(s)
- Marc Bonnet, Engineering Undecided, Lincoln University
Faculty Mentor(s)
- Ujjwal Das, Institute of Energy Conversion, University of Delaware
Abstract
Optical and Electrical Characterization of Boron Doped P-type Amorphous Silicon Thin Films for High Efficiency Silicon Heterojunction Solar Cell
By: Marc Bonnet
P-type amorphous silicon films are crucial to achieve low resistive contacts, enhanced
carrier transport, and p-n junction formation on n-type Si; but introduces parasitic absorption
loss. Therefore, an adequate optimization in terms of the optical and electrical properties of
p-type amorphous silicon films are essential to achieve high efficiency with an optimal thickness,
band gap, conductivity, and contact resistance of silicon heterojunction solar cells. The thickness
of a p-type amorphous silicon film is determined by performing an ultraviolet-visible
spectroscopy using a double beam instrument. An ultraviolet visible spectroscopy is used to
measure the transmittance and reflectance spectra of a thin film. The double beam instrument has
two light sources, a monochromator, and a series of mirrors to get the beam to a sample to be
analyzed. The transmittance and reflectance data are analyzed using a software called
“OPTICAL” that displays both the transmittance and the reflectance spectra. The software then
determines the thickness of the p-type amorphous silicon film by generating a line of best fit that
closely matches the lines of the transmittance and reflectance spectra.
The band gap of a p-type amorphous silicon film is the difference of energy between the
top of the valence band and the bottom of the conduction band. The band gap is also determined
by the software using Tauc’s plot. The conductivity of a p-type amorphous silicon film is
determined by measuring the lateral resistance between one metal contact pad to another metal
contact pad. The contact resistance of a p-type amorphous silicon film is determined by the
transfer length method, where a series of parallel metal contacts with increasing spacing is
formed on the thin film deposited on p-type Si. The transfer length method is used to calculate
the contact resistance, where the resistance between two adjacent metal pads is plotted as a
function of spacing. The resistance at zero spacing (Y-intercept of the linear fit) is equal to 2
times the contact resistance.