1. Nonaqueous Photoelectrochemistry of CH3NH3PbI3 Perovskite Thin Films and Single Crystal Wafers ES
Roghi Kalan, Alexander Carl, Ken Zielinski, Weiran Gao, Ronald Grimm*
Worcester Polytechnic Institute (WPI)
Worcester, Massachusetts

2. …will perovskite? What do we expect from perovskite crystal?
ECB Ef
EVB
What do we expect from perovskite crystal?
E(A+/A)
Voc should scale linearly with solution E(A+/A)
E(A+/A)
n-type
semiconductor
…silicon electrodes demonstrate this behavior…
Lewis, N. S. J. Electrochem. Soc. 1984, 131, 2496.
…will perovskite?

3. 1M Bu4NClO4/DCM (dichloromethane)
CH3NH3PbI3
Synthesized in-house
Working
Reference
Counter
300 W ELH
Illumination
1M Bu4NClO4/DCM (dichloromethane)
Back contact: GaIn/Ag
50mV/sec
Diced and polished
Si bandgap:1.11eV
Higher band gap, absorbs higher energy light. Pairing Si with a eV material. Perovskite band gap: ~1.55eV Perovskite has reached 22.1% efficiency alone. Recently, 25.5% was recorded with a tandem perovskite/Si cell.

4. J-E behavior of CH3NH3PbI3 crystal
Voc in DCM/Bu4NClO4 (V)
Redox couple
Cp2Fe+/0
Me2Cp2Fe+/0
Cp2Co+/0
n- Si
0.45
0.34
0.015
CH3NH3PbI3
0.70 ±0.15
0.5 ±0.1
0.25 ±0.1
Correct y-axis
Ideal semiconductor/liquid junctions (e.g. Si) show 1:1 Voc vs E(A/A–).Our hypothesis: Single crystal perovskite will demonstrate 1:1 in non-aqueous redox couple solutions. Perovskite crystals are stable in solvents such as THF and DCM. Currents are small due to cell resistance and poor solubility, however, Voc is unaffected. More redox couples will be tested to further understand photoelectro-chemical behavior and surface states.

5. J-E behavior of CH3NH3PbI3 Thin Film on FTO
Perovskite
Solution
Secondary solvent
in contact with Ferrocene/Ferrocenium,
red trace under illumination
and black trace in the dark
Leone, S, et al. Angew. Chem. 2014, 126, 10056
Zhou. Y, et al. J. Mater. Chem. A, 2015, 3, 8178

6. Tandem Solar Cells ? ? ? ? n+-Si
Perovskite ? ? ? ?
n+-Si
Monocrystalline Si efficiency, Theoretical: ~35%, Record:~25.6% Tandem/heterojunction solar cells can increase this efficiency. Adding light absorbing layer with a different band gap. Absorbs the light that otherwise passes through, or is lost by thermal relaxation by Si. Absorber has no intimate contact with Si, Hard to characterize the interface once it’s been made
One of our goals is to maintain a pristine interface.

7. Suitable surface to deposit the perovskite
Recombination
problem
Bisquert, J, J. Phys. Chem. Lett, 2013, 4, 2597
Grimm, R.L. et al., J. Phys. Chem. C 2012, 116, 23569

8. 3-aminopropyltriethoxysilane (3-APTES)
Coating with
3-aminopropyltriethoxysilane (3-APTES)
0.1 % in Toluene
room Temp
15min-24h
This layer would also act as a passivation layer against oxidation in air and caustic perovskite solutions.
XPS data,
Control exp for VOc
Surface characterization
Pasternak. R, et. Al, Langmuir, 2008, 24, 22, 12963

9. Peak area ratio SiO/N SiO/Si 15min 2.2 0.3 1h 1.2 0.5 12h 1.15 0.7 24h
0.8
26.7
15 min
SiOx
Si 2p
-NH3+
-NH2 1h
-NH2
-NH3+
SiOx
Si 2p
12h
-NH2
-NH3+
SiOx
Si 2p
24h
-NH2
-NH3+
SiOx
Si 2p

10. J-E of CH3NH3PbI3 film on ammonium term. Si
0.05
0.025
-0.025
-0.05
in contact with Ferrocene/Ferrocenium,
red trace under illumination
and black trace in the dark
Current density, J (mA cm-2)

11. amine terminated silicon
Perovskite on the
amine terminated silicon

12. Is there a better route to ammonium functionalization?
Take-home lessons
This layer would also act as a passivation layer against oxidation in air and caustic perovskite solutions.
XPS data,
Control exp for VOc
Methylammonium lead iodide / liquid junctions demonstrate Voc changes with solution redox potential.
Degenerate Si behaves as an Ohmic back contact, but deposition and selective contact need attention.

13. www.wpi.edu/+gg And Thanks for your attention
Funded by
WPI Chemistry and Biochemistry Department start up funds
And Thanks for your attention
WPI campus, just 45 miles away