1. ISMS 2016 Urbana, IL Vura-Weis Group - UIUC
Ultrafast Extreme Ultraviolet Spectroscopy of Methylammonium Lead Iodide Perovskite
Max Verkamp, Ming-Fu Lin, Elizabeth Ryland, Josh Vura-Weis
ISMS 2016
Urbana, IL
Vura-Weis Group - UIUC

2. Outline Motivation Technique Carrier specificity and dynamics in PbI2
“Hot” carrier relaxation in CH3NH3PbI3

3. Perovskite Structure (ABX3) Visible Absorption CH3NH3PbI3
Hybrid organic-inorganic perovskites reached >20% photovoltaic efficiency within 5 years.
Perovskite Structure (ABX3)
Visible Absorption
Band Gap
CH3NH3PbI3
G. Giorgi and K. Yamashita, J. Mater. Chem. A, 2014

4. The nature of above-band excitation of CH3NH3PbI3 has not been confirmed with traditional methods.CB
Split VB
480 nm
760 nm
Split CB & VB VB
Xing, G. C. Science 2013, 342,
Manser, J. S. and Kamat, P. V. Nat. Photon. 2014, 8,
Marchioro, A. PhD. Thesis, 2014
Residual PbI2
CT States
Wang, L. J. Am. Chem. Soc. 2014, 136,
Stamplecoskie, K. G. Energy Environ. Sci. 2015, 8,

5. Electron and hole dynamics can be observed independently through extreme ultraviolet transitions.CB
Visible pump VB
XUV probe ~
I 4d

6. High-Harmonic Generation (HHG) produces extreme ultraviolet (XUV) light via a non-linear process.1 2 3
Driving laser E field
time
800 nm Ne
~20 nm
XUV
1: Tunnel ionization
2: Propagation
3: Recombination
Potential Energy

7. High-Harmonic Generation (HHG) produces extreme ultraviolet (XUV) light via a non-linear process.

8. XUV measurements show the difference in conduction band shape between perovskite and PbI2.
CH3NH3PbI3 CB
Iodide partial density of states
PbI2
I 4d

9. Transient absorption of PbI2 show independent signals for electrons and holes.CB
Excited State
Absorption (hole)
Bleach (electron)
3.1 eV
2.5 eV VB
400 nm pump
1 μJ/pulse
1 kHz

10. The carrier specific signals in PbI2 arise within the instrument response, then decay into a new signal.

11. The carrier specific signals in PbI2 arise within the instrument response, then decay into a new signal.
IRF = 59 fs
τ = 5.8 ps

12. The carrier specific signals in PbI2 arise within the instrument response, then decay into a new signal.
IRF = 59 fs
τ = 5.8 ps

13. Tests with a heated sample cell confirmed the high temperature nature of the long-lived state.

14. Tests with a heated sample cell confirmed the high temperature nature of the long-lived state.

15. PbI2 Summary On to CH3NH3PbI3
Carrier specific signals were observed at 48 and 51 eV.
The recombination of these carriers generated heat, observable in the XUV transient spectrum.
IRF = 59 fs, τ = 5.8 ps
On to CH3NH3PbI3

16. Transient absorption of CH3NH3PbI3 fits with a “hot” hole excitation.CB
Excited State
Absorption (hole)
Bleach (electron)
1.6 eV
3.1 eV VB
400 nm pump
0.35 μJ/pulse
1 kHz

17. The hole signal in perovskite relaxes towards the band edge over the course of picoseconds.CB
1.6 eV
3.1 eV VB

18. Conclusions Acknowledgments
XUV spectroscopy probes electron and hole dynamics separately and independently.
Excitation in PbI2 results in signals for independent carriers within the instrument response that decay with a 5.8 ps time constant coupled to an increase in temperature in the sample.
Above band excitation in CH3NH3PbI3 results in a “hot” hole that relaxes towards the band edge in the first 2 ps.
Vura-Weis Group
Dr. Ming-Fu Lin
Springborn Endowment
AFOSR YIP FA
Acknowledgments