Upload
others
View
4
Download
0
Embed Size (px)
Citation preview
Kanazawa Institute of TechnologyOptoelectronic Device System Research & Development Center
Optoelectronic Device System R&D CenterKanazawa Institute of Technology
JAPAN
Present status and future prospects for super low-cost Cu2O-based solar cells
Toshihiro Miyata and Tadatsugu Minami
Materials Research and Technology 2018, Paris Feb. 19, 2018
1. Introduction
2. Fabrication procedure of heterojunction Cu2O solar cells
3. Photovoltaic properties for various n-type multicomponent oxide thin films/Cu2O heterojunction solar cells
4. Conclusion
Outline
・ Bandgap energy (Eg)≒2.1eV(direct-gap)
Background
Cuprous oxide (Cu2O)
Metal thin film/p-Cu2O Schottky barrier(SB) solar cellsn-type oxide semiconductor/p-Cu2O heterojunction solar cells
It is very difficult to achieve a high efficiency because of the difficulty of obtaining an n-Cu2O semiconductor. (Usually Cu2O have p-type conduction by intrinsic acceptor from Cu Vacancy.)
p-Cu2O
・ Non-toxic, low-cost
Long attracted much interest for application as an active layer in solar cells・ Theoretical energy conversion efficiency ≒ 20%
O
O
O Cu
CuVCu
h+p-Cu2O
Au
light
polycrystallineMetal thin film
electrode
n-type oxide semiconductor
膜厚が40-80[nm]の範囲において5[%]以上のηが得られ、膜厚が75[nm]において5.38[%]の高いηを実現できた。
Structure Eff.[%] Yare Ref.
SiO2/Cu/p-Cu2O 1.76 1982 1)
Al:ZnO(AZO)/p-Cu2O 1.20 2004 2)
Ga:ZnO(GZO)/p-Cu2O 1.52 2006 3)
MgF2/ITO/ZnO/p-Cu2O 2.01 2006 4)
FTO/ZnO/p-Cu2O 1.28 2007 5)
AZO/p-Cu2O(RTA treatment) 2.18 2011 6)
AZO/Sn-Pd/p-Cu2O 2.13 2011 6)
AZO/p-Cu2O(RTA treatment) 2.19 2011 6)
AZO/n-ZnO/p-Cu2O 4.12 2011 7)
AZO/n-Zn0.9Mg0.1O/p-Cu2O 4.29 2012 8)
AZO/n-Ga2O3/p-Cu2O 5.38 2012 9)
1)L.C.Olsen et al. Sol. Cells 7, 240(1982).
Bulk
5) Izaki, et al, J. Phys. D., 40, (2007) 3326.
2) T. Minami et al. Jpn.J.Phys., 43,pp-917-919 (2004).3) T. Minami et al. Thin Solid Films 528 (2013) 72.4) A. Mittiga, et al, J. Phys. D., 40, (2007) 3326.
Bulk Low damagedepositionmethods
Thinfilm
6) Y. Nishi et al. Thin Solid Films 520 (2012) 3819.7) Y. Nishi et al. Thin Solid Films 528 (2013) 72.8) T. Minami et al. ECS Transactions 8 (2012),
Honolulu, PRiME 2012 Photovoltaics for the 21st Century, in press.9) T. Minami et al, Appl. Phys. Express 6 (2013) 044101.
Structure and conversion efficency for Cu2O-based solar cells
An investigation of new n-type semiconductor thin film materials are very important for improvement of photo voltaic propartes of Cu2O heterojunction solar cells
★AZO/n-type semiconductor thin film /Cu2O heterojunction solar cells
4.130.609.690.71ZnO
Voc[V] Jsc[mA/cm2] FF η[%]
Ga2O3 0.80 9.99 0.67 5.38
n-typesemiconductor
1. Introduction
2. Fabrication procedure of heterojunction Cu2O solar cells
3. Photovoltaic properties for various n-type multicomponent oxide thin films/Cu2O heterojunction solar cells
4. Conclusion
Outline
Cu sheet (3×3[cm], thickness:0.2[mm])
Preparation method of p-type Cu2O sheet
Cu sheet p-type Cu2O sheet
1cm
14)
Resistivity ρ[Ωcm] 300-1000
Hall mobility μ[cm2/Vs] 100-120
hole concentrations
[cm-3]3-9×10 13
Air
Tem
pera
ture
[℃]
Time [min]30 60 60 120 120 60
1000
500 Ar Ar
0
14) Jian Li et al., J. Appl. Phys., 1021 (1991) 69.
Electrical properties ofpoly-crystal Cu2O sheet
1cm 1cm 1cm
Small grain size
Large grain size
Surface image of poly-crystal Cu2O sheet
Preparation methods of n-type multicomponent oxide thin film and AZO
Laser light source ArF Excimer laserWavelength [nm] 193
Repetition rate [Hz] 20
Pulse Laser Deposition (PLD)
Substrate RotatorLamp Heater
SubstrateView
PortPlume
Target
Lens
ArFExcimer Laser
O2 gas
p-Cu2O
Au electrode
AZO electrode
n-type Oxide thin film
1. Introduction
2. Fabrication procedure of heterojunction Cu2O solar cells
3. Photovoltaic properties for various n-type multicomponent oxide thin films/Cu2O heterojunction solar cells
4. Conclusion
Outline
Voltage V [V]0.10
2
4
6
8
12
Cur
rent
Den
sity
J[m
A/c
m2 ]
10
0.2 0.3 0.70.50.4 0.6
RT[℃] AZO/ZnO/Cu2O
0.8
150[℃]
300[℃]
AZO/ZnO/Cu2O
Deposition temperature dependence of J-V characteristics for AZO/ZnO/Cu2O solar cells
AZO/ZnO/Cu2O
-2 -1 0 1 2
103
10-210-110
0101102
Voltage V [V]
Cur
rent
Den
sity
J[m
A/c
m2 ]
10-3
0-4
Deposition Temperature[℃]
200
1
RT
:RT
200
temperatureFilm deposition
RT 200℃
2 nm2 nm
5 nm 5 nm
50nm 50nm
ZnOZnO
ZnOZnO
Cu2OCu2O
Cu2OCu2O
Carbon
ZnOZnO Cu2OCu2O
Carbon
EQE observed from AZO/ZnO/Cu2O solar cells fabricated with various deposition temperatures (R.T. And 200 [℃])
Deposition temperature dependence of the J-V characteristic obtained in AZO/ZnO/Cu2O heterojunction
solar cells measured under dark conditions.
Cross TEM images of AZO/ZnO/Cu2O heterojunction solar cells fabricated with various deposition temperatures
Objective
Sn Ti SiGe Group Ⅳ
GroupⅢ2 3
χφ
(GaIn)2O3
ZnGa2O4
(Ga:0.9)
Multicomponent Oxides as an n-type Semiconductor Layer
:3.2~4[eV]:4.1~5[eV]:4.9~5.2[eV]Eg
(Ga:0.975)Optimal Ga Content
2 32 3
GroupⅡ
CdO
MgO(ZnO)
χφ:4.6~4.8[eV]
:2.9~3.2[eV]
:1.95~2.1[eV]Eg
Cu2OWork function
Electron affinity
Energy gap
1
32η
[%]
0
4
0.05 0.15
5
Mg/(Mg+Zn) atomic ratio0.200.10
Optimal Mg Content: 0.09
Conversion efficiency:η
χ
φ
:3.5-3.7[eV]:4.54[eV]:3.6[eV]Eg
:2.5[eV]:8.8[eV]
:4.3~4.5[eV]:3.7~4.6[eV]:3.3~3.6[eV]
χφ
Eg
χ:2.5[eV]:7.8[eV]Eg
χ
Eg
Cu2O Heterojunction solar cells are prepared by using Ga2O3-based multicomponent oxide thin film as a n-type layer◎ Optimaization of the component
◎ Improving of band arrangement
Function n-type multicomponent oxide thin film Transparent electrode
Target (Ga2O3)X-(Al2O3)1-X AZO
Atmosphere O2 gas O2 gas
(Pressure[Pa]) (1.7[Pa]) (0.2 [Pa])Deposition temperature
[℃] RT RT
Film thickness [nm] 50 200
AZO and n-type Multicomponent Oxide Thin Film Deposition Conditions
p-Cu2OAu(back electrode)
AZO thin film
Multicomponent oxide thin film(50[nm])
Substrate RotatorLamp Heater
SubstrateView
PortPlume
Target
Lens
ArFExcimer Laser
O2 gas
Objective
(c) (Ga2O3)X-(Al2O3)1-X
2 3χ
φ
:3.5-3.7[eV]:4.54[eV]:3.6[eV]Eg
χφ
(GaIn)2O3
:3.2~4[eV]:4.1~5[eV]:4.9~5.2[eV]Eg
ZnGa2O4
2 3
2 3:2.5[eV]:8.8[eV]
χ
Eg
O2=1.7[Pa]
1.0
Voltage V [V]0
2
4
6
8
Cur
rent
Den
sity
J[m
A/c
m2 ]
10
0.2 0.80.4 0.6
12
1.0
0.975
Ga Content X [ratio]
0.9
0.8
0.1 0.3 0.5 0.7 0.9
0.95
Obtained FF η Jsc and Voc as functions of Ga content (X)for AZO/(Ga2O3)X-(Al2O3)1-X/Cu2O solar cells.
4
8
0.2
0.4
0.6
0.4
0.6
0.2
12
4.0
2.0
0
1.0
FFVo
c[V
]
Jsc
[mA
/cm
2 ]η
[%]
6.0
0.8
0
0 0
(Ga2O3)
(Ga2O3) (Ga2O3)
(Ga2O3)
η
FF Jsc
Voc
0.90 0.85 0.800.951.0 0.850.95 0.90 0.801.0
0.850.95 0.90 0.801.00.850.95 0.90 0.801.0
Ga Content X [ratio] Ga Content X [ratio]
Ga Content X [ratio] Ga Content X [ratio]
Obtained FF η Jsc and Voc as functions of Ga content (X)for AZO/(Ga2O3)X-(Al2O3)1-X/Cu2O solar cells.
Voltage [V]-2.0 -1.0 0 1.0
Cur
rent
[mA
]
0
2.0
-0.52.0
1.0
1.5
0.5
1.00.9750.950.90.8
Ga Content X [ratio]
100R
s[Ω
/cm
2 ] 200
Rs
0(Ga2O3)
0.850.95 0.90 0.801.0Ga Content X [ratio]
AZO/(GaXAl1-X)2O3/Cu2O
AZO/Ga2O3/Cu2O
Objective
Sn Ti SiGe Group Ⅳ
GroupⅢ2 3
χφ
(GaIn)2O3
ZnGa2O4
(Ga:0.9)
Multicomponent Oxides as an n-type Semiconductor Layer
:3.2~4[eV]:4.1~5[eV]:4.9~5.2[eV]Eg
(Ga:0.975)Optimal Ga Content
2 32 3
GroupⅡ
CdO
MgO(ZnO)
χφ:4.6~4.8[eV]
:2.9~3.2[eV]
:1.95~2.1[eV]Eg
Cu2OWork function
Electron affinity
Energy gap
1
32η
[%]
0
4
0.05 0.15
5
Mg/(Mg+Zn) atomic ratio0.200.10
Optimal Mg Content: 0.09
Conversion efficiency:η
χ
φ
:3.5-3.7[eV]:4.54[eV]:3.6[eV]Eg
:2.5[eV]:8.8[eV]
:4.3~4.5[eV]:3.7~4.6[eV]:3.3~3.6[eV]
χφ
Eg
χ:2.5[eV]:7.8[eV]Eg
χ
Eg
Cu2O Heterojunction solar cells are prepared by using ZnO-based multicomponent oxide thin film (Zn-Ge-O) as a n-type layer◎ Optimaization of the component
◎ Improving of band arrangement
J-V characteristics for AZO/ Zn1-XGeX-O /Cu2O:Na solar cells using various Ge content
0
2
4
6
8
10
0.2 0.4 0.6 0.8
Cur
rent
Den
sity
J[m
A/c
m2 ]
Voltage V [V]1.21.0
Ge Content [at.%]
0
30
62
12
(ZnO)
100 (GeO2)
0.5
1.0
2
4
8
12
η[%
]Js
c[m
A/c
m2 ]
0
0
4
6
1.5
Jsc:Current density
FF:Fill factor
η:Efficiency
Voc:Open circuit voltage
0
8
20 60 1000 40 80Ge Content [at.%](ZnO) (GeO2)
0.4
0.6
0
0.2
0.8
Voc
[V]
FF
Zn2GeO4
1.2[V]
6.67[%]
Ge=62[%]
40
0
Rs
[Ω/c
m2 ]
20 60 1000 40 80Ge Content [at.%](ZnO) (GeO2)
80
120Rs:Series resistance
Ge content dependence of photovoltaice properties for AZO/ Zn1-XGeX-O /Cu2O:Na solar cells
Dark J-V characteristics for AZO/ Zn1-XGeX-O /Cu2O:Na solar cells using various Ge content
GeO2 ZnO
Voltage V [V]-2 -1 0 1 2
Cur
rent
Den
sity
J[m
A/c
m2 ]
10-3
10-2
100
101
102
10-5
10-1
10-4
0
10062
30
Ge Content:[at.%]103
400 500 600Wavelength [nm]
EQ
E1.0
0.8
0.6
0.4
0.2
0350 450 550
0%30.2%
100%
Ge Content [at.%]
61.8%
300 650
EQE spectra for AZO/ Zn1-XGeX-O /Cu2O:Na solar cells using various Ge content
Ev
Ec
Eg=1.96[eV]Cu2O:Na
GeO2Eg=6.00[eV]
=0.87[eV]
Zn0.38Ge0.62OEg=5.00[eV]
=0.04[eV]Ec
Zn0.38Ge0.62O/Cu2OΔ
Zn0.70Ge0.30OEg=4.08[eV]
=0.66[eV]Ec
Zn0.70Ge0.30O/Cu2OΔ
ZnOEg=3.34[eV]
=1.03[eV]Ec
ZnO/Cu2OΔ
GeO2=0[at.%] Ge=30[at.%] Ge=62[at.%] Ge=100[at.%]
As the Ge composition increased, ΔEc decreased and ΔEc reached a minimum (about 0.04 [eV]) at a Ge composition of 62% at which the highest conversion efficiency was obtained
・
Reduction of ΔEc suppressed recombination at the interface・
The decrease of Jsc and FF over the Ge composition of 70 [%] or more is due to the formation of TYPE I junction・
Deposition technology Vacuum deposition methodDeposition material MgF2
Deposition temperature [℃] RT
Film thickness[nm] 75(Determined by simulation)
Atmosphere(pressure[Pa]) Vacuum(10-4)
Deposition technology and deposition conditions for MgF2
Deposition conditions for MgF2 thin film (anti reflection film)
0
20
40
60
80
100
300 350 400 450 500 550 600 650 700
反射
率/ %
波長 / nm
Reflectance properties of MgF 2 film
wavelength 300-600[nm]
Average reflectance reduction: about 8.4[%]
MgF2/AZO/n-(Ga0.975Al0.025)2O3/p-Cu2O:Na soler cells
material Film thickness[nm]MgF2 78AZO 200
n-(Ga0.975Al0.025)2O3 50 p-Cu2O ∞
with MgF2 antireflection film
no MgF2 anti reflection film
η
6.0
4.0
8.0
2.0
10.0
0
η[%
]
40 60 7050Ge Content [at.%]
Voc
1.0
1.5
0.5
0
80
Voc
[V]
7.53[%]
Oxygen pressure:4.0[Pa] Film thickness :50[nm]
Element temperature is constant at 25[℃]
Simulated sunlight (AM1.5G):100[mW/cm2]
Ge content :(Ge/(Ge+Zn)×100)[%]
light
Na doped p-Cu2O(p-Cu2O:Na)
ZnO:Al(AZO)
Zn1-XGeX-O
Ge content dependence of photovoltaic properties of MgF2/AZO/ Zn1-XGeX-O /Cu2O:Na solar cells
▲ : with MgF2 ○ : no MgF2
MgF2
η[%
]
η
6.0
2.0
8.0
Oxygen Pressure [Pa]
4.0
03.0 3.5 4.0 4.5 5.0
Voc
1.0
1.5
Voc
[V]
0.5
0
7.94[%]
Na doped p-Cu2O(p-Cu2O:Na)
ZnO:Al(AZO)
Zn1-XGeX-O
MgF2
MgF2/AZO/Zn0.38Ge0.62-O/Cu2O:Na太陽電池の光起電力特性の酸素ガス圧依存性
▲ : with MgF2 ○ : no MgF2
light
Oxygen pressure dependence of photovoltaic properties of MgF2/AZO/Zn0.38Ge0.62-O/Cu2O:Na solar cells
Film thickness :50[nm]
Element temperature is constant at 25[℃]
Simulated sunlight (AM1.5G):100[mW/cm2]
Ge content :62[%]
η
Jsc
Voc
FF4
8
0.2
0.4
0.6
6.0
4.0
800
1.0
FFVo
c[V
]
Jsc
[mA
/cm
2 ]η
[%]
10.0
40
0 0
0100
1.5
12
Film thickness[nm]
0.8
60
0.5
8040 10060 8040 10060
8040 10060
8.0
2.0
Film thickness[nm]
Film thickness[nm]
Film thickness[nm]
0
0 0
0
MgF2/AZO/Zn0.38Ge0.62-O/Cu2O:Na太陽電池の光起電力特性の酸素ガス圧依存性Film thickness dependence of photovoltaic properties of MgF2/AZO/Zn0.38Ge0.62-O/Cu2O:Na solar cells
8.23[%]
Oxygen pressure:4.0[Pa] Element temperature is constant at 25[℃]Simulated sunlight (AM1.5G):100[mW/cm2]Ge content :62[%]
MgF2/AZO/Zn0.38Ge0.62-O/Cu2O:Na太陽電池の光起電力特性の酸素ガス圧依存性Film thickness dependence of photovoltaic properties of MgF2/AZO/Zn0.38Ge0.62-O/Cu2O:Na solar cells
0
12
10
0.2 0.4 0.6 1.0
Cur
rent
Den
sity
J[m
A/c
m2 ]
Voltage V [V]0.8 1.2
2
4
6
8
8.23 0.6310.801.20η[%] Voc[V] Jsc[mA/cm2] FF
Oxygen pressure:4.0[Pa] Element temperature is constant at 25[℃]Simulated sunlight (AM1.5G):100[mW/cm2]Ge content :62[%]
Film thickness :57[nm]
Conclusion
◎AZO/n-type multicomponent oxide thin film/p-Cu2O solar cells
1) Photo voltaic properties are not only dependent on the component of metal element but also preparation conditions.
2) The efficiency was improved by using multicomponent oxide thin film as a n-type layer, such as Ga-Al-O and Zn-Ge-O.
3) The highest conversion efficiency of 8.23% could be achieved in a MgF2/AZO/ Zn0.38-Ge0.62-O/Cu2O:Na heterojunction solar cell fabricated using a 75-nm-thick Zn0.38-Ge0.62-O thin film and a Cu2O:Na sheet with a P of approximately 4×1015 cm-3.