Small Number of Defects per Nanostructure Leads to “Digital” Quenching of Photoluminescence: The Case of Metal Halide Perovskites

Abstract

in devices. Solution processability implies the presence of a high concentration of crystal defects, making many new materials inefficient emitters and poor conductors. The primary energy loss channel is the nonradiative (NR) recombination of excited electrons and holes assisted by charge trapping. [2] Rationalizing the charge recombination mechanisms, the properties of the NR recombination centers and their origin are crucially important for technological applications. The case of MHPs is very peculiar and seems contradictory. Low temperature solution processing with very fast crystallization under the condition of kinetic competition between many processes should lead to high concentrations of crystal defects. However, somehow it is not a severe problem for device efficiency. [2-5] Here it is important to realize that not every defect leads to NR recombination, and even if some do, their efficiency can vary

Experimental Evidence of Chloride‐Induced Trap Passivation in Lead Halide Perovskites through Single Particle Blinking Studies

“…These trap dynamics are often assigned to ion migration. [6] In these experiments, a gradual decrease in PL intensity upon illumination can be observed. A comparable PL decrease has been reported for MAPbI 3 microcrystals [33] and CsPbI 3 quantum dots (QDs) [34] and may arise from perovskite degradation.…”

“…These traps result in efficiency losses by nonradiative recombination. [5,6] Despite the use of sophisticated synthetic techniques and strictly controlled reaction conditions, the formation of harmful native defects during OMHP crystal growth cannot be avoided. [5,7] For example, MAPbI 3 exhibits high trap densities in both polycrystalline (10 16 -10 21 cm -3 ) and single crystalline (10 10 cm -3 ) morphologies.…”

Presence of Maximal Characteristic Time in Photoluminescence Blinking of MAPbI3 Perovskite

“…This means that PLQY does not depend on the concentration of charge carriers, which, however, is not true for a bulk semiconductor. [34] A detailed analysis of the PLQY dependence on charge carrier concentration as demonstrated by Kiligaridis et al [70] could be the foundation for the quantitative theory. Detailed theory and modeling on PL blinking of large MAPbI 3 crystals will be published elsewhere.…”

“…[19,21] Thus, PL yield depends on the actual number of metastable nonradiative recombination centers per crystal which fluctuates in time and depends on other conditions. [34] Conceptually, this model is same as the multiple recombination center (MRC) model proposed a decade ago as one of the explanations Photoluminescence (PL) blinking is a common phenomenon in nanostructured semiconductors associated with charge trapping and defect dynamics. PL blinking kinetics exhibit very broadly distributed timescales.…”

“…[35] PL blinking phenomenon was used to estimate charge transport in MHPs, find the spatial location of the metastable defects using super-resolution optical imaging and spectroscopy, assess their charge recombination cross sections, and to unravel the nature of the nonradiative recombination centers. [16][17][18][19][20][21][22][23]34,36] Rationalizing PL intensity fluctuations in individual emitters is an active research field for the last 25 years where the largest body of literature is devoted to PL blinking of colloidal semiconductor QDs. [35,[37][38][39][40][41][42][43][44] Blinking of semiconductor QDs, nanorods, nanoplates, and nanowires usually show a wide range of timescales from milliseconds to hours.…”