Microstructure analysis of n-doped μ c-SiO x :H reflector layers and their use in stable a-Si:H p-i-n cells. Pavel Babal * , Johan Blanker, Ravi Vasudevan, Arno Smets, and Miro Zeman Photovoltaic Materials and Devices, Delft University of Technology. *. Motivation.
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Microstructure analysis of n-doped μc-SiOx:H reflector layers and their use in stable a-Si:H p-i-n cells
Pavel Babal*, Johan Blanker,
Ravi Vasudevan, Arno Smets,
and Miro ZemanPhotovoltaic Materials and Devices, Delft University of Technology
Microcrystalline hydrogenated silicon oxide (c-SiOx:H) has been successfully applied in solar cells, improving their performance, yet the microstructure of this material is not fully understood. Parameters of c-SiOx:H layers have been optimized and the heterogeneous microstructure has been studied with Raman and FTIR spectroscopy revealing correlations between deposition parameters, the material properties of c-SiOx:H, and solar cell performance. c-SiOx:H/Ag back reflectors have been integrated in a-Si:H single junction cells, achieving through improved light trapping an initial efficiency of 11.1%. The best stable efficiencies are achieved for cells with an intrinsic a-Si:H film of around 200 nm.
n-doped μc-SiOx:H development and characterization
Raman analysis to study crystalline grains
Table of trends associated with increase in each parameter; s=strong trend, w=weak trend, σ=conductivity, n600=refractive index at 600 nm, k600=absorption coefficient at 600 nm, EA=activation energy, Ebg=bandgap.
Raman spectroscopy of n-doped c-SiOx:H. The peak is left of the 521 crystalline silicon peak, evidence of 4-6 nm silicon crystal grains.
Raman peak overview of the CO2 (a) and pressure (b) series.
FTIR analysis to study a-SiOx:H tissue
Gaussian fits of FTIR scans for 2 c-SiOx:H recipes. A microcrystalline sample deposited with pressure of 2 mbar (top) and an amorphous sample deposited with a H2:SiH4 ratio of 0 (bottom).
Assignments of wagging and stretching modes in c-SiOx:H.
Changes in normalized relative contributions of different stretching modes in c-SiOx:H as a function of pressure, CO2:SiH4, and H2:SiH4. Yellow regions show amorphous material.
Solar cell integration of n-μc-SiOx:H
Higher stable efficiency with varying i-layer thickness
JSC improvement with varying μc-SiOx:H thickness
for optimized recipe
EQE spectra of degraded cells with c-SiOx:H and different H2 diluted i-layer thicknesses.
EQE of a-Si cells with different thicknesses of c-SiOx:H. *Cell has double standard a-Si n-layer thickness.
Initial and degraded (in brackets) parameters of cells with different R=5 i-layer thickness.
*) Contact:Pavel Babal
2628 CT, Delft Netherlands [email protected]
Photovoltaic Materials and Devices Laboratory