Gary Hodes

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