Cadth 2015 a2 cadth symposium2015 panel_valuingmedicaltech_13april2015_clessard
Electrodeposition of Solar Grade Silicon Films from Molten...
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Direct reduction of SiO 2 nanoparticles on graphite substrate resulting in photoactive p-type polycrystalline silicon film Silicon carbide (SiC) formation at silicon-graphite interface, indicating Si-C bond is formed at the initial stage of deposition, strengthening adhesion between silicon and graphite Some pinholes between Si crystallites exposing graphite substrate Taeho Lim 1,2 , Ji Zhao 1,2 , and Allen J. Bard 1,2,* 1 Department of Chemistry, The University of Texas, Austin TX 78712 2 Center for Electrochemistry, The University of Texas, Austin TX 78712 Why Electrodeposition of Solar Grade Silicon from Molten Salt? Future work Preparation and Characterization of Electrodeposited Silicon Films Effect of Impurities on P hotoelectrochemical Characteristics of Photoactive Silicon Film Direct reduction of SiO 2 nanoparticles at cathode Graphite (C) as both anode and cathode material Stainless steel-capped quartz vessel Electrodeposition of Silicon f rom Molten Salt ① Optimization of silicon electrodeposition process by controlling parameters such as substrate, chemical purity, current density, potential, counter electrode material, and cell configuration ② Controlling dopant of electrodeposited silicon with various dopants to construct a p-n junction by control of bath composition and/or conventional methods of p-n junction formation ③ Scaling-up and fabrication of solar devices by using optimal silicon electrodeposition process in order to transfer to industry and deployment to developing countries *Photovoltaic (PV) System Pricing Trends, 2014 Ed., SunShot *Forbes SunShot target: $1/W for utility- scale PV system by 2020 Low production cost for solar grade silicon films via electrodeposition Low energy consumption of Si electrodeposition (13 kWh/kg Si), compared to conventional Siemens process (80 kWh/kg Si) Photoelectrochemical cell (PEC ) test Cathode: SiO 2 + 4e - Si + 2O 2- Anode: C + 2O 2- CO 2 (g) + 4e - Liquid junction formation instead of solid-state junction Fast and accurate test method Redox couple: ethyl viologen (EV 2+ /EV + ) in acetonitrile Electrodeposition of Silicon Film from CaCl 2 Molten Salt -Proposed Mechanism- Light (100 mW /cm 2 ) Typical Liquid Junction for p-Type Si h + e - E redox E F Silicon Solution CB VB E g Pinhole SEM SiO 2 nanoparticles e - O 2- Graphite substrate Si Si crystallites Secondary Ion Mass Spectroscopy Depth Profile of Electrodeposited Silicon film Positive ion mode Negative ion mode Impurities in Si films Impurity Concentration after Pre - electrolysis Impurity concentration Estimated dopant concentration from Mott-Schottky plot XRD Pattern XPS Spectra of Si 2p XPS Spectra of C 1s SiC Si C C: Si: Major impurities (Ca, Cl, Mg, Al, Mn) originating from CaCl 2 molten salt Most impurities located at the surface of electrodeposited silicon and interface between silicon film and graphite substrate Successive deposition of silicon films from the same molten salt resulting in reduction of impurity concentrations in silicon film 5000 Hz 6300 Hz 7940 Hz 10000 Hz PEC test Crucible & Pre - electrolysis Leveling impurity concentration down by using a quartz crucible and introduction of pre-electrolysis Reduction of dark current by decreasing number of pinholes and/or impurity concentration 30% of photocurrent (@-0.6 V, vs. Ag/0.01 M AgNO 3 ) of single crystalline p-type silicon wafer (5-10 ohm·cm) Light on Light off Summary Photoactive p-type polycrystalline silicon film was successfully formed via electrodeposition in CaCl 2 molten salt. Most impurities, such as Ca, Cl, Mg, Al, and Mn, were located at the surface of electrodeposited silicon and interface between silicon and graphite substrate. Major impurities (Mg, Al) in bulk silicon film were suspected as p-type dopants, which make electrodeposited silicon film exhibit p-type electrochemical photoresponse. Impurity concentration of electrodeposited silicon film was leveled down by adopting a quartz crucible and pre-electrolysis method. 30% of photocurrent (@-0.6 V, vs. Ag/0.01 M AgNO 3 ) of single crystalline p-type silicon wafer (5-10 ohm·cm) was obtained with electrodeposited silicon film; the relatively low photocurrent of the silicon film probably results from a fair amount of grain boundaries acting as minority carrier recombination centers. EV 2+ EV + Acknowledgement Electrodeposition of Solar Grade Silicon Films from Molten Salt
Transcript of Electrodeposition of Solar Grade Silicon Films from Molten...
Direct reduction of SiO2 nanoparticles on graphite substrate resulting in photoactive p-type polycrystalline silicon film
Silicon carbide (SiC) formation at silicon-graphite interface, indicating Si-C bond is formed at the initial stage of deposition, strengthening adhesion between silicon and graphite
Some pinholes between Si crystallites exposing graphite substrate
Taeho Lim1,2, Ji Zhao1,2, and Allen J. Bard1,2,*
1Department of Chemistry, The University of Texas, Austin TX 787122Center for Electrochemistry, The University of Texas, Austin TX 78712
Why Electrodeposition of Solar Grade Silicon
from Molten Salt?
Future work
Preparation and Characterization of Electrodeposited Silicon Films
Effect of Impurities on Photoelectrochemical Characteristics of Photoactive Silicon Film
Direct reduction of SiO2 nanoparticles at cathode
Graphite (C) as both anode and cathode material
Stainless steel-capped quartz vessel
Electrodeposition of Silicon from Molten Salt
①Optimization of silicon electrodeposition process by controlling parameters such as substrate, chemical purity, current
density, potential, counter electrode material, and cell configuration
②Controlling dopant of electrodeposited silicon with various dopants to construct a p-n junction by control of bath
composition and/or conventional methods of p-n junction formation
③ Scaling-up and fabrication of solar devices by using optimal silicon electrodeposition process in order to transfer to
industry and deployment to developing countries
*Photovoltaic (PV) System Pricing Trends, 2014 Ed., SunShot
*Forbes
SunShot target: $1/W for utility-
scale PV system by 2020
Low production cost for solar grade
silicon films via electrodeposition
Low energy consumption of Si
electrodeposition (13 kWh/kg Si),
compared to conventional Siemens
process (80 kWh/kg Si)
Photoelectrochemical cell (PEC) test
Cathode: SiO2 + 4e- Si + 2O2-
Anode: C + 2O2- CO2(g) + 4e-
Liquid junction formation instead of solid-state
junction
Fast and accurate test method
Redox couple: ethyl viologen (EV2+/EV+) in
acetonitrile
Electrodeposition of Silicon Film from CaCl2 Molten Salt
-Proposed Mechanism-
Light (100 mW/cm2)
Typical Liquid Junction for p-Type Si
h+
e-
EredoxEF
Silicon Solution
CB
VB
Eg
Pinhole
SEM
SiO2 nanoparticles
e-
O2-
Graphite substrate
Si
Si crystallites
Secondary Ion Mass Spectroscopy Depth Profile of Electrodeposited Silicon film
Positive ion mode Negative ion mode
Impurities in Si films
Impurity Concentration after Pre-electrolysis
Impurity concentrationEstimated dopant concentration
from Mott-Schottky plot
XRD Pattern XPS Spectra of Si 2p XPS Spectra of C 1s
SiC
SiC
C:
Si:
Major impurities (Ca, Cl, Mg, Al, Mn)
originating from CaCl2 molten salt
Most impurities located at the surface
of electrodeposited silicon and interface
between silicon film and graphite
substrate
Successive deposition of silicon films
from the same molten salt resulting in
reduction of impurity concentrations in
silicon film
5000 Hz 6300 Hz 7940 Hz 10000 Hz
PEC test
Crucible
&
Pre-electrolysis
Leveling impurity concentration down by
using a quartz crucible and introduction
of pre-electrolysis
Reduction of dark current by decreasing
number of pinholes and/or impurity
concentration
30% of photocurrent (@-0.6 V, vs.
Ag/0.01 M AgNO3) of single crystalline
p-type silicon wafer (5-10 ohm·cm)
Light on
Light off
Summary
Photoactive p-type polycrystalline silicon film was successfully formed via electrodeposition in CaCl2 molten salt.
Most impurities, such as Ca, Cl, Mg, Al, and Mn, were located at the surface of electrodeposited silicon and interface between silicon and graphite substrate.
Major impurities (Mg, Al) in bulk silicon film were suspected as p-type dopants, which make electrodeposited silicon film exhibit p-type electrochemical photoresponse.
Impurity concentration of electrodeposited silicon film was leveled down by adopting a quartz crucible and pre-electrolysis method.
30% of photocurrent (@-0.6 V, vs. Ag/0.01 M AgNO3) of single crystalline p-type silicon wafer (5-10 ohm·cm) was obtained with electrodeposited silicon film; the
relatively low photocurrent of the silicon film probably results from a fair amount of grain boundaries acting as minority carrier recombination centers.
EV2+
EV+
Acknowledgement
Electrodeposition of Solar Grade Silicon Films
from Molten Salt
