Extremely Thin Absorber (ETA) solar cells Gary Hodes, Yafit Itzhaik, Eran Edri, Elena Rabinovich, Nir Klein, Michael Kokotov and Hagai Cohen Dept. of Materials and Interfaces and Dept. of Chemical Research Support, Weizmann Institute of Science
VV
Funding Fundacion Chile, AERI (Weizmann Institute of Science), Israel Ministry of Science, Culture and Sport,
What is a semiconductor-sensitized nanoporous solar cell? nanoporous TiO2
light absorption depth
eh+ light-absorbing semiconductor
h+ e500 nm
ZnO nanorod film
Basic mechanism of ETA solar cell porous oxide (TiO2 or ZnO) coated with light absorbing semiconductor
V
Electricallyconducting glass
EC CuSCN
hole conductor (electrolyte, CuSCN) to remove holes
EV
metal contact
h+ e-
Separation of electric charge generated by light to give electricity
e-
h+
TiO2
Electron microscope side view of the cell
Au
CuSCN
Blowup of porous TiO2
TiO2/absorber/CuSCN
dense TiO2 (~120 nm) 500 nm
conducting glass
Various absorbers: CdSe, CdS, Cu2-xS, Sb2S3 Some properties of Sb2S3 Usually deposited by low temp. methods as amorphous Sb2S3 Eg ~2.2 eV Converts to crystalline stibnite ~250ยบC bandgap
~1.75 eV direct (ca. 720 nm)
Melting point
550ยบC
Oxidation to Sb2O3
300ยบC
Abundance of Sb
Similar to In but more available
Fabrication of the cells (using Sb2S3 as example of absorber)
CuSCN infiltration (from PrCN soln.) anneal Sb2S3 In(OH)S ‘buffer’ (CBD) dense TiO2 (spin coat)
Au evap/sputt
Li(K)SCN aqueous soln. treat Sb2S3 (CBD) porous TiO2 (spin coat)
FTO glass
Sb2S3
Inx(OH)ySz TiO2 CuSCN
P25/In-OH-S/Sb2S3/KSCN/CuSCN 0.15 cm2
3.37% (AM1) 3.4%
3.8%
Band gap eV 1.7-1.8
70 60
area 0.7 cm2 EQE 1 sun illumination % VOC 525 mV ISC 13.4 mA/cm2 FF 38% efficiency 2.7%
50 40 30 20
T %
15
10
dark
5
10 0 350
450
illuminated 550 650 wavelength (nm)
Y. Itzhaik et al. J. Phys. Chem. C, 113, 4254 (2009)
20
0 750
Transmission (%)
(0.1 AM1)
External Quantum Efficiency (%)
80
Change CuSCN to Spiro-OMeTAD S.-J. Moon, Y. Itzhaik, Ju-H. Yum, S. M. Zakeeruddin, G. Hodes, and M. Gr채tzel, J. Phys. Chem. Lett. 1, 1524 (2010)
3.1%
4.0%
5.2%
ZnO instead of TiO2 as electron conductor Electron microscope side view of the cells Au
CuSCN
ZnO + CdS + CuSCN
TiO2 + CdS + CuSCN
conducting glass
1 !m
N. Kedem, E. Edri, M. Kokotov, H. Cohen, T. Bendikov R. Popovitz-Biro, P. von Huth, D. Ginley and G. Hodes. Crystal Growth & Design. 10, 4442, (2010).
Treatment of ZnO nanorod surface S2- treatment of ZnO for absorber coverage (0.1 M Na2S room temperature 10 min) ZnO
+ CBD CdS
ZnO/S2-
CdS NH3/thiourea
CdS thioacetamide
CdSe
ED ZnO/CdS
E. Edri, E. Rabinovich O. Niitsoo, H. Cohen, T. Bendikov and G. Hodes. J. Phys. Chem. C, 114, 13092, (2010).
Best ZnO/CdS/CuSCN cells without and with S2- treatment
2
J (mA/cm2)
1
dark
0
light -1
-2
0
200
400 V (mV)
600
800
Diagnostic: CuSCN/ZnO dark I-V
ZnO + S2ZnO ZnO:0.14% Sb ZnO:Sb + S2-
Summary/Conclusions Sb2S3 is a very promising absorber for ETA cells. Very high quantum efficiencies
Energy diagram mapped for the TiO2/Sb2S3/CuSCN cell
ZnO has very different characteristics compared to TiO2 but also promising for cells
Na2S treatment of ZnO improves semiconductor coverage of ZnO