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

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

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

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, 344-347 Manser, J. S. and Kamat, P. V. Nat. Photon. 2014, 8, 737-743 Marchioro, A. PhD. Thesis, 2014 Residual PbI2 CT States Wang, L. J. Am. Chem. Soc. 2014, 136, 12205-12208 Stamplecoskie, K. G. Energy Environ. Sci. 2015, 8, 208-215

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

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

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

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

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

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

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

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

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

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

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

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

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

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 FA9550-14-1-0314 Acknowledgments