Trap States and Their Dynamics in Organometal Halide Perovskite Nanoparticles and Bulk Crystals

Abstract

Organometal halide perovskites have attracted tremendous attention for optoelectronic applications. Charge carrier trapping is one of the dominant processes often deteriorating the performance of devices. Here, we investigate the details of trap behavior in colloidal nanoparticles (NPs) of CH 3 NH 3 PbBr 3 perovskites with mean size of 8 nm and the corresponding bulk crystals (BCs). We use excitation intensity dependence of photoluminescence (PL) dynamics together with comprehensive simulation of charge carrier trapping and the trap-state dynamics. In the bulk at very low excitation intensities the PL is quenched by trapping. A considerable fraction of the traps become filled if excitation fluence is increased. We identified two different traps, one exhibiting ultralong lifetime (∼70 μs) which leads to efficient accumulation of trap filling even at relatively low excitation intensities. In colloidal NPs, the average number of surface traps is estimated to be 0.7 per NP. It means about 30% excitation would undergo trap-free radiative recombination. The trapping time constant of 7 ns is orders of magnitude longer than the usual trapping times in typical colloidal quantum dots indicating semipassivation of the trap states by a large barrier which slows down the process in the perovskite NPs. We also note that due to the localized character of photogenerated electron−hole pairs in NPs the trapping efficiency is reduced compared to the freely moving charges in BCs. Our results offer insight into the details of photophysics of colloidal perovskite nanoparticles which show promise for light-emitting diode and laser applications.

Enhancing photoluminescence yields in lead halide perovskites by photon recycling and light out-coupling

“…We attribute this monomolecular non-radiative recombination to a trap-assisted Shockley-Read-Hall recombination, which has been reported before and studied in detail253637. The processes of carrier trapping, de-trapping and subsequent recombination can be described in more detail, but this is beyond the scope of this work.…”

Synthesis and Photoluminescence Properties of 2D Phenethylammonium Lead Bromide Perovskite Nanocrystals

“…The layered perovskite forms a semiconductor/insulator multi‐quantum‐well system within which the inorganic semiconducting sheets composed of PbX 6 4− octahedra act as the wells and the surrounding insulating organic layers act as barriers . Such systems provide electronic and optical properties different from bulk materials . Benefiting from the flexibility of material selection of both the organic and inorganic moieties, a variety of atomically thin films of organic–inorganic perovskite materials can be synthesized to form a library of 2D materials .…”

Doping and Photon Induced Defect Healing of Hybrid Perovskite Thin Films: An Approach Towards Efficient Light Emitting Diodes

“…The trade‐off, however, is an increase in surface defects as shown by Chen et al. in their recent report, where trap‐assisted non‐radiative recombination increases exponentially with decreasing NC size ,. Moreover, thermal annealing causes the conglomeration of these NCs, adding to the formation of additional defects ,…”

“…PL spectroscopic measurements have shown a significant change in the PLQY by varying excitation power. This change can be attributed to a high density of defect or trap sites . Low PLQY in bulk perovskites is often a result of non‐radiative recombination due to trapping of the long‐lived charge carriers.…”