Broadband Fluorescence Up-Conversion Spectroscopy : A Powerful Tool to Assess Ultrafast Dynamics of Charge Carriers and Excitons in Lead Trihalide Perovskites
Etienne Socie a, Jacques-E. Moser a
a Group for Photochemical Dynamics, Institute of Chemical Sciences & Engineering, École Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, Switzerland
Proceedings of International Conference on Hybrid and Organic Photovoltaics (HOPV19)
Roma, Italy, 2019 May 12th - 15th
Organizers: Prashant Kamat, Filippo De Angelis and Aldo Di Carlo
Poster, Etienne Socie, 240
Publication date: 11th February 2019

Time-resolved fluorescence spectroscopy is a powerful tool to investigate the photo-luminescence dynamics of semiconductor systems on the femtosecond timescale. Available experimental techniques, such as those based on the use of streak cameras or time-correlated single photon counting (TCSPC) are limited by a temporal resolution of a few picoseconds [1]. A resolution of at most 0.2-0.5 ps, however, is deemed necessary to monitor the early events occurring during the relaxation of hot carriers and the formation of excitons in direct bandgap materials. To allow for such a time-resolution, the emission of the sample can be upconverted (gated) by sum-frequency mixing with an ultrashort pulse in a nonlinear optical crystal.

Here, we are presenting a new broadband (λ = 420-750 nm) fluorescence up-conversion setup (FLUPS) developed by Ernsting et al. [2], which allows single-scan pump-gate measurements. The time resolution of the FLUPS instrument is only limited by the gate pulse duration and has been found to be < 200 fs for our setup. A spectral discrimination of less than 50 cm–1 is achieved, moreover, using an unfolded Czerny-Turner spectrometer for signal detection.

We demonstrate the ability of FLUPS by investigating the early-time evolution of the fluorescence of two-dimensional lead trihalide perovskites. The rise of the photoemission of such 2-D films has been found to be of the order of 0.9 ps to 1.2 ps, depending on the cation and fluence, which is well above the experimental response function. A deeper analysis of the kinetics of the fluorescence rise will provide insights into the dynamics of the charge carriers and pseudo-particles upon light excitation of low-dimensionality perovskites of various compositions and architectures.

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