Electronic processes in organo-metal-halide perovskite nano-crystals probed at the individual crystal level

Daniela Täuber^a, Aboma Merdasa^a, Yuxi Tian^a, Alexander Dobrovolsky^a, Ivan Scheblykin^a

^aLund University, Department of Chemical Physics, Getingevägen 60, Lund, 22241, Sweden

Materials for Sustainable Development Conference (MATSUS)
Proceedings of September Meeting 2016 (NFM16)

Berlin, Germany, 2016 September 5th - 13th

Organizers: Marin Alexe, Enrique Cánovas, Celso de Mello Donega, Ivan Infante, Thomas Kirchartz, Maksym Kovalenko, Federico Rosei, Lukas Schmidt-Mende, Laurens Siebbeles, Peter Strasser, Teodor K Todorov, Roel van de Krol and Ulrike Woggon

Oral, Ivan Scheblykin, presentation 430
Publication date: 14th June 2016

Despite of the great progress reached in solar cells based on organo-metal-halide (OMH) perovskites, many fundamental aspects of photoluminescence and charge recombination are far from been understood. Although at the first approximation OMH perovkites can be seen as direct semiconductors, presence of defects, mechanical softness of the material, ion migration, unusual dielectric properties due to the organic molecule in the crystal structure, formation of crystals of different sizes and topologies makes their optical and electrical properties quite peculiar.Here we present several phenomena observed by analysis of luminescence of micro- and nanocrystals of CH3NH3PbI3.

We employed luminescence spectroscopy of individual OMH perovskite nano-crystals and electron microscopy for the very same sample in order to correlate the sample morphology and properties beyond the ensemble averaging.

In the presentation I will discuss spatial inhomogeneity of the PL intensity and lifetime and PL enhancement by light irradiation.[1,2] We relate these phenomena to the presence of charge carrier traps which concentration depends not only on the sample, but also on the environment (oxygen, nitrogen, vacuum) and light irradiation conditions.

Another interesting phenomenon that we observed was an enhancement of PL of CH3NH3PbI3 in the phase transition temperature region from 130 to 160K in individual nanocrystals. This effect has a direct connection to formation of nano-sized domains of different crystals phases in the transition region temperature.

We also employed 2-dimensional polarization imaging and found for the first time that individual crystals possess PL polarization degree up to 70% at low temperature while the PL excitation was not polarized. Comparing our data with polarization-resolved theoretical calculations of the electronic states will hopefully enable a fully consistent model of the electronic transitions in OMHPs to be obtained.

[1] Y. Tian, M. Peter, E. Unger, M. Abdellah, K. Zheng, T. Pullerits, et al., Mechanistic insights into perovskite photoluminescence enhancement: light curing with oxygen can boost yield thousandfold, Phys. Chem. Chem. Phys. 17 (2015) 24978–24987

[2] Y. Tian, A. Merdasa, E. Unger, M. Abdellah, K. Zheng, S. McKibbin, et al., Enhanced Organo-Metal Halide Perovskite Photoluminescence from Nanosized Defect-Free Crystallites and Emitting Sites, J. Phys. Chem. Lett. 6 (2015) 4171–4177

[3] Y. Tian, A. Merdasa, M. Peter, M. Abdellah, K. Zheng, C.S. Ponseca, et al., Giant Photoluminescence Blinking of Perovskite Nanocrystals Reveals Single-Trap Control of Luminescence, Nano Lett. 15 (2015) 1603–1608

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