Thin film halide perovskite as a triplet fusion sensitizer: present status and open questions
Frederik Eistrup a, Klaus Schwarzburg a, Sergiu Levcenco a, Dennis Friedrich a, Thomas Unold a, Klaus Lips a, Eva Unger a b, Rowan MacQueen a
a Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Germany, Berlin, Germany
b Department of Chemistry & NanoLund, Lund University, Sweden
nanoGe Fall Meeting
Proceedings of nanoGe Fall Meeting19 (NGFM19)
#Exciup19. Excitonic up-downconversion
Berlin, Germany, 2019 November 3rd - 8th
Organizer: Bruno Ehrler
Oral, Rowan MacQueen, presentation 331
Publication date: 16th July 2019

Sensitized triplet fusion upconversion occurs via the collision of triplet-excited annihilator molecules [1]. The optically dark triplet states are populated by triplet sensitizers, which usually consist of molecule-like absorbers such as semiconductor nanocrystals, organometallic complexes, or thermally active delayed fluorescence molecules. In a new approach to triplet sensitization, intended to remove the usual excitonic character of the triplet sensitizer, electron-hole pairs optically excited in a thin film of lead halide perovskite semiconductor are used to drive triplet formation and subsequent triplet fusion upconversion in an adjacent small molecule layer. The approach is reminiscent of an organic light-emitting diode, with key differences arising from the simple bilayer nature of the device. Recent results show that this is a viable approach to implementing triplet fusion upconversion, although the efficiency of the system is thus far modest [2]. In this work, we present our current understanding of the thin film perovskite triplet sensitization mechanism, and discuss the potentials and pitfalls for this method of photon upconversion. We also examine the broader implications of the process as an example of radiationless energy transfer at a hybrid semiconductor interface, and discuss how this may shed light on the nature of surface states in thin film lead halide perovskites.

RWM acknowledges funding support from the Helmholtz Association Initiative and Networking Fund. We thank Prof. John Anthony of the University of Kentucky for provision of the TIPS-tetracene. The authors thank Carola Klimm of Helmholtz-Zentrum Berlin for conducting SEM measurements. We acknowledge PicoQuant for lending the LDH-P-C-705 laser diode head used in this study.

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