Verification of Type-A and Type-B-HC Blinking Mechanisms of Organic–Inorganic Formamidinium Lead Halide Perovskite Quantum Dots by FLID Measurements

Abstract

Organic-inorganic halide perovskite nanocrystals or quantum dots (PQDs) are excellent candidates for optoelectronic applications, such as lasers, solar cells, light emitting diodes, and single photon sources. However, the potential applications of PQDs can expand once the photoluminescence, and in particular, the blinking behaviors of single PQDs are understood. Although the blinking of PQDs has been studied extensively recently, the underlying mechanism of the blinking behaviors is still under debate. In this study, we confirmed that type-A and type-B-HC (hot carrier) blinking, contributed to PQD blinking using their fluorescence lifetime intensity distribution (FLID). Type-B-HC blinking was experimentally confirmed for the first time for formamidinium based PQDs, and the simultaneous contributions of type-A and type-B blinking were clearly specified. Further, we related different FLID data to the ON/ OFF time distribution as distinct features of different blinking types. We also emphasized that detection capability was crucial for correctly elucidating the blinking mechanism.Lead halide perovskites quantum dots (PQDs) have been successfully used as materials for next-generation optoelectronic devices, such as solar cells, light emitting diodes, lasers, and single photon sources 1-7 . Their primary advantages lie in their large absorption cross-section, high photoluminescence (PL) quantum yield, narrow PL spectral width, wide-range emission tunability, feasibility for scale-up synthesis, and cost-effectiveness 8-12 . Despite their advantages, blinking and irreversible photo-degradation of PQDs have been frequently reported and could limit their optical performance 13,14 .Classifying blinking scenarios into type-A and type-B has been widely accepted. Type-A blinking mechanism is attributed to charging and discharging processes. When quantum dots (QDs) are charged owing to carrier transfer to trapped states, the non-radiative Auger recombination of the trion state competes with the radiative recombination to quench photon emission by transferring its exciton energy to the extra carrier (electron or hole), which results in low PL emission (OFF state). The high PL emission (ON state) is recovered by neutralizing the QDs 15-17 . Type-B blinking is attributed to the activation and deactivation of multiple recombination centers (MRCs) [17][18][19] , which are short-lived traps (e.g., shallow traps) in QDs 17-20 . The activation and deactivation of MRCs modulate the non-radiative recombination rates, and thus, cause PL intensity fluctuations 20 . These two types of blinking mechanisms could be used for conventional semiconductor QDs 15-20 and also, possibly, for PQDs 13,21-23 . In addition, several researchers have suggested in their recent publications, that the two types of blinking simultaneously contribute to PQD blinking [24][25][26][27] .Analysis of fluorescence lifetime intensity distribution (FLID) has been regarded as a very effective experimental approach to distinguish between these two types of blinking mech...

Real-Time Blinking Suppression of Perovskite Quantum Dots by Halide Vacancy Filling

“…Recently, the type-B blinking behavior was subcategorized into (i) the trapping of a hot carrier that does not intervene in the observed PL lifetime and (ii) the trapping of a band-edge carrier or the presence of shallow traps. In the latter case, the PL intensity linearly decreases with the PL lifetime because of the short-lived trap states. , Kim et al . associated the shallow traps with the type-B (i) and (ii) mechanisms, and the deep traps with the type-A mechanism.…”

“…classified the blinking behavior of such QDs into two mechanisms, namely, type-A and type-B, which are respectively due to the nonradiative Auger recombination and the hot-electron trapping processes . These mechanisms were verified in halide perovskite microcrystals (HPMCs), nanocrystals (HPNCs), and quantum dots (HPQDs). − , In the type-A blinking, the ON- and OFF-events occur by charging and discharging of an HPQD, whereas the type-B blinking occurs by trapping–detrapping of charge carriers. These processes were analyzed using the plots of the ON- and OFF-time probability distributions and the fluorescence lifetime intensity distributions (FLIDs).…”

“…Also, the structure and properties of these perovskites are susceptible to moisture, heat, and light. − Although perovskites are termed defect-tolerant, , the deep or shallow traps formed by the B-site cation or halide vacancies, interstitial sites, and anti-sites deteriorate these perovskites . In particular, the vacancies become the centers of nonradiative recombination, adversely affecting the QE and contributing to the undesired photoluminescence (PL) fluctuations/blinking. − Thus, passivation of the halide vacancies and suppression of the PL blinking are inevitable for improving the properties and advancing the photonic/photovoltaic applications of perovskites.…”

“…These processes were analyzed using the plots of the ON- and OFF-time probability distributions and the fluorescence lifetime intensity distributions (FLIDs). Also, the type-A/B blinking concurrently occur in perovskites. − For example, Lee et al . explained that in formamidinium lead bromide (FAPbBr 3 ) QDs Auger ionization and electron transfer contribute to the two blinking mechanisms .…”

“…40 These mechanisms were verified in halide perovskite microcrystals (HPMCs), nanocrystals (HPNCs), and quantum dots (HPQDs). [29][30][31][32]44 In the type-A blinking, the ON-and OFF-events occur by charging and discharging of an HPQD, whereas the type-B blinking occurs by trapping−detrapping of charge carriers. These processes were analyzed using the plots of the ON-and OFF-time probability distributions and the fluorescence lifetime intensity distributions (FLIDs).…”