Ultrafast exciton and band gap renormalization in CH3NH3PbBr3 single crystals

Tania Palmieri^a, Edoardo Baldini^a, Majed Chergui^a, László Forró^b, Endre Horvath^b, Andrea Pisoni^b, Andreas Mann^b, Ana Akrap^c

^aInstitute of Chemistry and Chemical Engineering, École Politechnique Fédérale Lausanne, Station 6 CH-1015 Lausanne, Switzerland

^bInstitute of Physics (IPHYS), EPFL Ecole Polytechnique Federale de Lausanne, Switzerland, Station, Lausana, Switzerland

^cDepartment of Quantum Matter, Université de Genève, 24 quai Ernest Ansermet, 1211 Geneva, Switzerland

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

Poster, Tania Palmieri, 442
Publication date: 14th June 2016

Organo-metal halide perovskite-based solar cells have witnessed an incredibly fast emergence in the last years. This success is primarily due to the rapid increase in conversion efficiency, now approaching 21% [1], and to the low manifacturing costs that make hybrid perovskite materials an attractive alternative to silicon. Moreover, the high photoluminescence quantum efficiency and the narrow and tunable emission band that characterize these semiconductors, make them the perfect candidate for high-performance optoelectronic devices [2]. In order to optimise these unique features, detailed understanding of the photophysics of organo-metal halide perovskites is needed.

In this regard, ultrafast spectroscopy is a powerful approach to reveal the dynamics of charge carriers and gain a deeper insight into the phenomena governing the behaviour of these materials. Here, we perform femtosecond broadband transient-reflectivity measurements on solution-grown single crystals of CH₃NH₃PbBr₃. We tune the pump photon energy to 3.1 eV, in order to excite uncorrelated electron-hole pairs well above the bandgap energy (2.4 eV) at different pump fluences. The high temporal resolution of our experimental setup (<50 fs) [3] allows to follow the evolution of the sample reflectivity in the first hundreds of fs, revealing how the resonant exciton at the absorption onset is affected by the many-body dynamics of the photoinduced carriers. We complement these results with equilibrium ellipsometry in a broad spectral range. Our approach gives access to the evolution of the sample complex optical conductivity without the need of a Kramers-Kronig analysis.

[1] Chen et al, Science 350.6263 (2015)

[2] Tan et al. Nature Nanotechnology (2014)

[3] Mann et al. Physical Review B 92.3 (2015)

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