Modulation of Excited State Dynamics in Lead Halide Perovskite Films with Electrical Bias
Gergely Samu a b c, R.A. Scheidt c d, A. Balog a, C. Janáky a b, P.V. Kamat c d
a Department of Physical Chemistry and Materials Science, Interdisciplinary Excellence Centre, University of Szeged, Rerrich Square 1, Szeged, Hungary
b ELI-ALPS Research Institute, Szeged, Dugonics sq. 13, 6720, Hungary
c Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, IN 46556
d Radiation Laboratory, Department of Chemistry & Biochemistry, University of Notre Dame, Notre Dame, Indiana 46556, EE. UU., Notre Dame, United States
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
Oral, Gergely Samu, presentation 189
Publication date: 11th February 2019

In recent years the emergence of hybrid organic-inorganic lead halide perovskites revitalized several semiconductor related research fields. This growing interest is mainly caused by the rapid efficiency increase of derived solar cells, which reached 22.3% in the past 10 years. To unravel the reasons behind their outstanding performance, it is important to understand their optoelectronic properties, especially their excited state dynamics under operating conditions.

Spectroelectrochemical methods are viable tools to determine fundamental optoelectronic properties (band edge and trap state energies) and electrochemical bias induced chemical changes in these materials.1 However, to probe charge carrier dynamics, it is essential to utilize ultrafast laser techniques, as the related processes fall into the femto- or picosecond timescale.

In my presentation the effect of applied bias on the charge carrier dynamics of perovskite electrodes will be discussed. Ultrafast spectroelectrochemical experiments were carried out on FTO/TiO2/CsPbBr3 system by coupling ultrafast transient absorption spectroscopy with electrochemical techniques.2 It was found that the excitonic feature of CsPbBr3 is responsive to the applied external bias, within the materials electrochemical stability window. The accumulation of electrons on the TiO2/CsPbBr3 interface had a pronounced effect on charge carrier lifetimes in CsPbBr3. This change in charge carrier lifetimes was completely reversible, showing the dependence of excited state dynamics on the externally controlled charge carrier density. This validates the in situ electrochemical transient absorption measurement as a useful tool to probe the charge carrier injection process in different semiconductor systems.

Samu, G. F., Scheidt, R. A., Kamat, P. V. & Janáky, C. Electrochemistry and Spectroelectrochemistry of Lead Halide Perovskite Films: Materials Science Aspects and Boundary Conditions. Chem. Mater. 30, (2018).

Scheidt, R. A., Samu, G. F., Janáky, C. & Kamat, P. V. Modulation of Charge Recombination in CsPbBr3 Perovskite Films with Electrochemical Bias. J. Am. Chem. Soc. 140, 86–89 (2018).

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