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@PHDTHESIS{Lambertz:190115,
author = {Lambertz, Andreas},
title = {{D}evelopment of {D}oped {M}icrocrystalline {S}ilicon
{O}xide andits {A}pplication to {T}hin-{F}ilm {S}ilicon
{S}olar {C}ells},
school = {University Utrecht},
type = {Dr.},
address = {Utrecht},
publisher = {University Utrecht},
reportid = {FZJ-2015-03055},
pages = {177},
year = {2015},
note = {University Utrecht, Diss., 2015},
abstract = {The aim of the present study is the development of doped
microcrystalline silicon oxide (µc‑SiOx:H) alloys and its
application in thin‑film silicon solar cells. The doped
µc‑SiOx:H material was prepared from carbon dioxide
(CO2), silane (SiH4), hydrogen (H2) gas mixtures using
plasma enhanced chemical vapour deposition (PECVD) with
process conditions which are fully compatible with the
overall solar cell manufacturing processes. Doping was
achieved by adding phosphine (PH3) or trimethyl boron
B(CH3)3 to the process gas. Particular focus in the material
development is to establish the relationship between the
deposition process parameters and the material properties of
doped µc‑SiOx:H such as optical band gap, refractive
index, conductivity, and crystalline volume fraction. To
understand the individual influences of the different
structural phases of the composite material µc‑SiOx:H the
link between the optoelectronic properties and the material
structure as well as the material composition was
investigated. It is shown that doped µc‑SiOx:H material
is a mixture of crystalline silicon nanoparticles (highly
crystalline µc‑Si:H) and amorphous silicon oxide
(a‑SiOx:H), where the a‑SiOx:H phase itself consists of
a‑SiO2 and a‑Si:H. This is advantageous since an oxygen
rich amorphous silicon phase (a‑SiOx:H) has a wide optical
band gap, allowing to reduce optical losses in the device,
while a volume fraction of the highly crystalline µc‑Si:H
phase above a value as low as $30\%$ already ensures
sufficiently high electrical conductivity to reduce
electrical losses. The optical properties such as optical
band gap and refractive index of the doped µc‑SiOx:H
films can be conveniently adjusted over a wide range by the
CO2/SiH4 gas flow ratio. The crystalline volume fraction at
a given CO2/SiH4 ratio can be increased by decreasing the
silane concentration SC = SiH4 / (SiH4 + H2). The ideal
preparation conditions to obtain optimum material were
identified and the resulting doped µc‑SiOx:H layers were
evaluated in single and tandem junction solar cells. To
establish a link between the µc‑SiOx:H material
properties and the solar cell performance the research
addresses the parasitic absorption of the doped layers and
the in‑coupling of light to reduce optical losses and gain
more photocurrent in the device. Additionally, the device
stability against light exposure was investigated for a
variety of absorber layer thicknesses. It was shown that in
a‑Si:H/µc‑Si:H tandem solar cells the thickness of the
absorber layer of the a‑Si:H top cell can be reduced,
without impairing device efficiency, by incorporation of
µc‑SiOx:H as intermediate reflector. Most importantly,
such thinner cells show improved stability yielding a
stabilized efficiency of $10.3\%$ for single junction solar
cells. It is concluded that doped µc‑SiOx:H can be
beneficially applied to thin‑film silicon solar cells,
reducing the parasitic absorption, improving
light‑incoupling, and acting as an intermediate reflector
thanks to the low refractive index and the wide band gap at
a sufficiently high conductivity.},
keywords = {Dissertation (GND)},
cin = {IEK-5},
cid = {I:(DE-Juel1)IEK-5-20101013},
pnm = {121 - Solar cells of the next generation (POF3-121)},
pid = {G:(DE-HGF)POF3-121},
typ = {PUB:(DE-HGF)11},
url = {https://juser.fz-juelich.de/record/190115},
}