Bandgap and Carrier Dynamic Controls in CsPbBr3 Nanocrystals Encapsulated in Polydimethylsiloxane

Lianxing Liao,Kunhua Quan,Tao Lin,Ruosheng Zeng,Xiangshi Bin

doi:10.3390/cryst11091132

Abstract

Bandgap tunability through ion substitution is a key feature of lead halide perovskite nanocrystals (LHP-NCs). However, the low stability and low luminescent performance of CsPbCl3 hinder their full-color applications. In this work, quantum confinement effect (QCE) was utilized to control the bandgap of CsPbBr3 NCs instead of using unstable CsPbCl3, which possess much higher emission efficiency in blue spectra region. Studies of microstructures, optical spectra and carrier dynamics revealed that tuning the reaction temperature was an effective way of controlling the NC sizes as well as QCE. Furthermore, the obtained CsPbBr3 NCs were encapsulated in a PDMS matrix while maintaining their size distribution and quantum-confined optoelectronic properties. The encapsulated samples showed long-term air and water stability. These results provide valuable guidance for both applications of LHP-NCs and principal investigation related to the carrier transition in LHP-NCs.

Highlights

Lead halide perovskite (LHP) crystals, be they hybrid organic−inorganic MAPbX3(MA = CH3NH3+; X = Cl−, Br− and I−), FAPbX3 (FA = CH(NH2)2+) or their fully inorganic counterpart CsPbX3, have been attracting widespread attention since Kojima et al [1] demonstrated their high potentials in photovoltaic (PV) applications in 2009 [2,3,4]
Based on the time-resolved PL spectrum results, decay lifetimes of Wannier–Mott excitons were found increasing following the decrease of NC sizes. These results clearly indicated the contribution of quantum confinement effect (QCE) that led to the bandgap enlargement, which provided a well approach for tailoring the emission wavelength of Colloidal perovskite nanocrystals (CPNCs) that are with stable structure
CsPbBr3 NCs with 80–90% photoluminescent quantum yield (PLQY) were synthesized by a hot-injection method

Summary

Introduction

The cubic-phased CsPbBr3 crystals show green emission with photoluminescent quantum yield (PLQY) up to 90% and long-term stability, whereas cubic-phased CsPbCl3 or CsPbCl3–xBrx crystals are not stable at room temperature and show violet to blue emission with PLQY close to 1%, which degrade in few hours [17] These divergences are intrinsically based on differences in radii of the halide ions, which lead to difficulty in fabricating blue and violet light sources based on CPNCs and hinder their full-color applications. If the CPNC diameter is comparable or smaller than the exciton Bohr diameter, the quantum confinement effect (QCE) will lead to the broadening of bandgap and splitting of quasi-continuous in-band energy levels [18] This method has been proved effective in traditional IV, II-VI and III-V group semiconductor NCs [19,20,21,22]. Alivisatos et al [23] and Manna et al [24] reported the layer-by-layer growth of LHP nanoplatelets (NPLs) and their tunable emission due to QCE

Methods

Results

Conclusion