Exciton Binding Energy and the Nature of Emissive States in Organometal Halide Perovskites.

Summary, in English

Characteristics of nanoscale materials are often different from the corresponding bulk properties providing new, sometimes unexpected, opportunities for applications. Here we investigate the properties of 8 nm colloidal nanoparticles of MAPbBr3 perovskites and contrast them to the ones of large microcrystallites representing a bulk. X-ray spectroscopies provide an exciton binding energy of 0.32 ± 0.10 eV in the nanoparticles. This is 5 times higher than the value of bulk crystals (0.084 ± 0.010 eV), and readily explains the high fluorescence quantum yield in nanoparticles. In the bulk, at high excitation concentrations, the fluorescence intensity has quadratic behavior following the Saha-Langmuir model due to the nongeminate recombination of charges forming the emissive exciton states. In the nanoparticles, a linear dependence is observed since the excitation concentration per particle is significantly less than one. Even the bulk shows linear emission intensity dependence at lower excitation concentrations. In this case, the average excitation spacing becomes larger than the carrier diffusion length suppressing the nongeminate recombination. From these considerations we obtain the charge carrier diffusion length in MAPbBr3 of 100 nm.

• Author: Kaibo Zheng; Qiushi Zhu; Mohamed Qenawy; Maria Messing; Wei Zhang; Alexander Generalov; Yuran Niu; Lynn Ribaud; Sophie E Canton; Tönu Pullerits
• Department/s: Chemical Physics; Synchrotron Radiation Research; Solid State Physics; MAX IV Laboratory; NanoLund: Centre for Nanoscience
• Publishing year: 2015
• Language: English
• Pages: 2969-2975
• Publication/Series: The Journal of Physical Chemistry Letters
• Volume: 6
• Issue: 15
• Links: http://dx.doi.org/10.1021/acs.jpclett.5b01252
• Document type: Journal article
• Publisher: The American Chemical Society (ACS)
• Topic: Physical Chemistry
• Status: Published
• ISBN/ISSN/Other: ISSN: 1948-7185