Three ways to grow faster and better CIGSe:
In-Ga co-electrodeposition,
1 second laser annealing,
and Cu-rich growth
Phillip Dale1, Joao Malaquias1, Helen Meadows1, Marc Steichen1
Valérie Deprédurand2, Yasuhiro Aida2, Susanne Siebentritt2,
Ashish Bhatia3 and Mike Scarpulla3
(1) Laboratory for Energy Materials, University of Luxembourg (2) Laboratory for Photovoltaics, University of Luxembourg
Luxembourg Cu(In,Ga)Se2 processes
Electrodeposition Annealing Advantage
Talk outline
Electrodeposition Annealing Advantage
Electrodeposition and annealing
WE A V RE CE 1 inch Mo/Cu/In:Ga Electrodeposition of metals Tube furnace ΔT ~ 33 °C min-1 N2,H2 P ~ 10 mbar NH2 C NH2 O Solvent1.Co-electrodeposition of In and Ga could lead to more uniform electrodeposits on the microscale?
Advantages of electrodeposition from ionic liquids
-1.76 -0.76 -0.53 -0.34 0 +0.34 +0.74 Al Zn Ga In H Cu Se
E vs. NHE Aqueous electrodeposition limits
Mo Cu In 3+ H+ V Reference electrode
Ionic liquid electrodeposition window
Wider electrochemical window enables facile deposition of low reduction potential elements like Ga
Co-electrodeposition of In and Ga
Malaquias et al. Manuscript in preparation
Comparison to academic literature
Ga / III ratio controllable over the whole range
Adapted from Zank et al., Thin Solid
Films, 1996 , 286, 259
Coelectrodeposition of In-Ga on Cu
Depositions at Ed = -1.2 V ; constant Q; Ga/IIIobtained = 0.1; 0.4; 0.7 ; T = 60 °C - SEM/EDX Ga/III = 0.1 Ga/III = 0.7 5 µm 10 µm 1 µm Element Atomic % Cu 42.6 In 0.5 Ga 26.5 Element Atomic % Cu 4.6 In 88.5 Ga 4.8
Morphology changes with Ga content
Ga/III = 0.4
Best Preliminary Device Results
Ga/III = 0.4
1 µm
Talk outline
Electrodeposition Annealing Advantage
Electrodeposition and Laser Annealing
Cu2Se + In2Se3 + CuInSe2 Mo CuInSe2 Mo Energy + Se? Room temperature deposited precursor Absorber layerAdvantages of Laser Annealing? 1. heat just the local environment
2. absorber layer temperature can exceed glass softening temperature
Is it possible to anneal an absorber in 1 s?
What does annealing do?
Energy side
1. diffuse atoms to remove
concentration gradients (Cu, In, Se) 2. grow grains
3. drive chemical reactions
4. move defects to grain boundaries 5. move Na or O to pacify defects at grain boundaries
Cu2Se +
In2Se3 +
CuInSe2
Mo
chemical depth profiles
x-ray diffraction
Precursor
Cu2Se +
In2Se3 +
CuInSe2
Laser Annealing for 1s at 945 W.cm
-2Cu2Se +
In2Se3 +
CuInSe2
Mo
Laser Annealing at 945 W.cm
-2Cu2Se +
In2Se3 +
CuInSe2
Mo
FWHM of main peaks decreased after laser annealing indicating increased crystal coherence length
Opto – electronic properties
Cu2Se + In2Se3 + CuInSe2 Mo Furnace LaserLaser annealed absorber layer shows PL properties When completed to full device, shows rectification…
Talk outline
Electrodeposition Annealing Advantage
"Cu-rich": larger splitting of quasi-Fermi levels higher Voc potential Finished cells: actual resulting Voc drops at higher Cu-contents
splitting of quasi-Fermi levels not fully exploited for high Cu-contents Only absorber Finished solar cell
Quasi-Fermi level splitting in polycrystalline layers
Recombination path in Cu-poor and "Cu-rich"
1.0 1.2 1.4 1.6 0.8 1.0 1.2 1.4 1.6 Cu-poor Cu-rich x~0.25 x=0 x=0 x~0.25 y=0 Ac ti v ati on E nergy E a (eV)Band Gap Energy E
g (eV)
Turcu, Pakma, Rau, Appl. Phys. Lett., 80 (2002) 2598
Cu(In1-xGax)(Se1-ySy)
A new process for "Cu-rich" solar cells
"Cu-rich" bulk with Cu-poor surface:
540 °C CuInSe2 + CuxSe KCN etching Cu, In, Se co-deposition Stoichiometric CuInSe2 In-Se deposition 200 °C 1min + annealing (10wt%, 5min) Mo Mo Mo InSe 50nm Stoichiometric CuInSe2 -40 -30 -20 -10 0 10 20 30 40 50 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 0.6 Voltage (V) C u rr e n t d e n s it y ( m A /c m 2 )
VAL004E-1 Cu-rich, etched
VAL005E-2 InSe 200°C1min+ 275°Cannealing YA198 Cu-poor
currently best result: 13.1% efficiency
compare with
14.0% from Cu-poor
Why is the current low?
one reason:
space charge width is too short from capacitance measurements:
space charge width is smaller
the doping is too high!
Depredurand, Tanaka, Aida, Fevre, Siebentritt, submitted
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 300 500 700 900 1100 1300 EQE wavelength (nm) 1 - Cu/In=0.93 2 - Cu/In=0.96 3 - Cu/In=0.98 4 - Cu/In=1.18 5 - Cu/In=1.29 6 - Cu/In=1.71 25 35 45 55 65 75 85 950 1000 1050 1100 1150 1200 1250 EQE (%) wavelength (nm) QE measured Qe fitting
BUT: from QE collection length
diff SCR eff W L L Leff (Cu-rich) 3mm Leff (Cu-poor) 2mm
Then why is the current lower?
0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 300 500 700 900 1100 1300 EQE wavelength (nm) 1 - Cu/In=0.93 2 - Cu/In=0.96 3 - Cu/In=0.98 4 - Cu/In=1.18 5 - Cu/In=1.29 6 - Cu/In=1.71 25 35 45 55 65 75 85 950 1000 1050 1100 1150 1200 1250 EQE (%) wavelength (nm) QE measured Qe fitting QE lower by constant factor
reduced collection probability
high recombination in SCR due to tunneling 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 0.0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 300 500 700 900 1100 EQE wavelength (nm) NA=1.1016 NA=5.1016 QE4/QE3 QE5/QE3 QE6/QE3 QE/QE ratio
Depredurand, Tanaka, Siebentritt et al., submitted
Cu-poor vs. Cu-rich
band diagram:
collection function:
Cu-poor or
Summary
• Indium and Gallium can be simultaneously electrodeposited with good compositional control over a large potential range.
• Laser annealing of nanocrystalline CuInSe2 precursors for one second
Summary and Acknowledgements
• Indium and Gallium can be simultaneously electrodeposited with good compositional control over a large potential range
• Laser annealing of nanocrystalline CuInSe2 precursors for one second
is sufficient to diffuse elements, grow grains, and develop semiconductor products • Cu rich grown absorbers contain fewer defects and have a potential to produce higher Voc devices than Cu poor grown absorbers.
