Exciton Binding Energy and the Nature of Emissive States in Organometal Halide Perovskites.
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.
†Department of Chemical Physics, Lund University, Box 124, 22100, Lund, Sweden.
Kaibo
K
Zheng
§Department of Synchrotron Radiation Instrumentation, Lund University, Box 118, 22100, Lund, Sweden.
Qiushi
Q
Zhu
†Department of Chemical Physics, Lund University, Box 124, 22100, Lund, Sweden.|‡Department of Chemistry, Qena Faculty of Science, South Valley University, Qena 83523, Egypt.
Mohamed
M
Abdellah
∥Deptartment of Solid State Physics, Lund University, Box 118, 22100, Lund, Sweden.
Maria E
ME
Messing
†Department of Chemical Physics, Lund University, Box 124, 22100, Lund, Sweden.
Wei
W
Zhang
⊥MAX IV Laboratory, Lund University, Box 118, 22100, Lund, Sweden.
Alexander
A
Generalov
⊥MAX IV Laboratory, Lund University, Box 118, 22100, Lund, Sweden.
Yuran
Y
Niu
#X-ray Science Division, Advanced Photon Source and Materials Science Division, Argonne National Laboratory, Argonne, Illinois 60439, United States.
Lynn
L
Ribaud
∇IFG Structural Dynamics of (Bio)chemical Systems, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077 Goettingen, Germany.|○FS-SCS, Structural Dynamics with Ultra-short Pulsed X-rays, Deutsches Elektronen-Synchrotron (DESY), Notkestrasse 85, D-22607 Hamburg, Germany.
Sophie E
SE
Canton
†Department of Chemical Physics, Lund University, Box 124, 22100, Lund, Sweden.
Tõnu
T
Pullerits
D017610:Calcium Compounds / Q000737:chemistry*; D008163:Luminescent Measurements; D053758:Nanoparticles / Q000737:chemistry; D010087:Oxides / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D017785:Photons; D014025:Titanium / Q000737:chemistry*
D017610:Calcium Compounds; D010087:Oxides; C059910:perovskite; D014025:Titanium
exciton binding energy; fluorescence; nanoparticles; perovskites; photoelectron spectroscopy