Nonaqueous Photoelectrochemistry of CH3NH3PbI3 Perovskite Thin Films and Single Crystal Wafers ES3.10.07 Roghi Kalan, Alexander Carl, Ken Zielinski, Weiran Gao, Ronald Grimm* Worcester Polytechnic Institute (WPI) Worcester, Massachusetts www.wpi.edu/+gg

…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?

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 1.6-1.8eV material. Perovskite band gap: ~1.55eV Perovskite has reached 22.1% efficiency alone. Recently, 25.5% was recorded with a tandem perovskite/Si cell.

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.

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

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. http://all-len-all.com/tandem-silicon-perovskite-solar-cells-could-provide-solar-power-on-the-cheap/

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

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

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

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)

amine terminated silicon Perovskite on the amine terminated silicon

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.

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