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1. Photoinduced carrier dynamics of
CH3NH3PbI3 thin films
Ryuichi. Ito
Department of Electrical and Electronics
Engineering, University of Fukui

2. Contents
1. Introduction
2. Purpose
3. Experiments
4. Results
5. Conclusion

3. Contents
1. Introduction

4. Introduction
Perovskite structure
Unit cell of the CH3NH3PbI3
CH3NH3PbI3 has self –organizing
quantum well structure.
・Properties of ferroelectric
・Piezoelectric effect
・Photovoltaic material
Applications such as photovoltaic
solar cells and light-emitting devices
etc.

5. VB VB2
VB1
CB <200fs
CH3NH3PbI3TiO2
~0.7ps
~0.5ps
CB
1.55eV
Perovskite solar cell
It remains unknown about electron-lattice interaction and
carrier dynamics.
Time constants is reported.
• cooling time of CH3NH3PbI3
and TiO2.
Introduction
• electron transfer between
CH3NH3PbI3 and TiO2.

6. Contents
2. Purpose

7. We investigate transmittance spectra of CH3NH3PbI3 thin
film by pump probe spectroscopy.
Purpose
Observing carrier dynamics of
CH3NH3PbI3 directly and investigate details.
Method

8. Contents
3. Experiments

9. Pump-probe spectroscopy Measurement condition
Energy Power
Pump 1.55 eV
(800 nm)
2 mW
Probe 1.55 eV
(800 nm)
7 mW
Absorbance spectra of CH3NH3PbI3 thin film[4]
Experiments
[4]C. Wehrenfennig, G. Eperon, M. Johnston, H. Snaith and L. Herz: Adv. Mater. 26 (2014) 1584.

10. FTO
TiO2
CH3NH3PbI3
Production process
Synthesize hydriodic acid and
methylamine.
Dissolve neutralized salt and
lead iodide educed.
Fabricate CH3NH3PbI3 with
spin-coating.
PbI2+CH3NH3I →CH3NH3PbI3
Experiments
Sample : CH3NH3PbI3

11. Contents
4. Results

12. ①
②
① delay time < 1 [ps]
An aperiodic component near zero delay.
It is attributed to electron-lattice interaction.
② delay time > 1 [ps]
Exponential decay and absorption saturation.
It is attributed recombination of electrons
from TiO2 to CH3NH3PbI3
Results

13. Detail of ①
(An aperiodic component)
We use continuous wavelet
transform.
Results
Frequency component of
2~3 THz
It corresponds to phonon
in PbI2.
Phonon at CH3NH3PbI3 and
TiO2 interface is observed.
As a result

14. We found differential
transmittance corresponding to
back electron transfer.
VB VB2
VB1
CB <200fs
CH3NH3PbI3TiO2
~0.7ps
~0.5ps
CB
1.55eV
Back electron transfer …
Electron at the bottom of CB in
CH3NH3PbI3 is excited with pump pulse
(800nm) and transfer to the bottom of CB
in TiO2.
Then, it transfers to the top of VB in
CH3NH3PbI3
Results
The dephasing time is 26 [ps].
Detail of ②
(absorption saturation)

15. Contents
5. Conclusion

16. Conclusion
• We observed an aperiodic component near zero delay.
It corresponds to phonon in PbI2.
It is thought that phonon in PbI2 has an impact on carrier
transfer at interface.
• We observed absorption saturation correspond to back
electron transfer.
It can not be fitted well by single exponential fit.
We should use more appropriate fitting model for recombination.