Improved Stability and Exciton Diffusion of Self‐Assembled 2D Lattices of Inorganic Perovskite Nanocrystals by Atomic Layer Deposition

Abstract

colloidal synthesis in 2015, [2] ample work has been published featuring the excellent optoelectronic properties of these solutionprocessable materials, [3] from the emission tunability via size, composition, [2,4] and doping, [5] to the high quantum yields (QY) despite significant structural disorder. [6] These advantages make PNCs particularly suitable for a variety of applications such as solid-state lighting, [7] lasing, [8] solar cells, [9] and luminescent solar concentrators (LSCs). [10] Despite the vast literature devoted to understanding and optimizing their optical properties and some impressive proof of principle devices, [11] PNCs sensitivity to light, temperature, and environmental exposure has thus far prevented their use in widely functional optoelectronic devices. Moreover, such limited stability prevents a thorough study of excitons transport at the nanoscale, which is pivotal in understanding and optimizing the PNCs optoelectronic properties towards the realization of efficient devices. One way to assess their potential for optoelectronics application is by investigating their exciton transport with exciton diffusion measurements. Exciton diffusion mediated by Förster resonance energy transfer (FRET) is responsible for very efficient energy transport in several processes in nature, for instance photosynthesis, but also in artificial systems, such as in quantum dots (QDs) solids. [12] In the latter case, it is possible for an exciton to hop onto an adjacent QD by FRET mechanism, provided that other conditions for FRET beyond the short distance are met, for instance a significant degree of spectral overlap between the emission spectrum of the excited QD and the absorption spectrum of the ground state QD that is receiving the exciton. Our group has recently demonstrated FRET-mediated transport in a carefully engineered system that allowed to create long-range ordered 2D lattices of close-packed PNCs [13] and obtain a record transport of 200 nm, [13] one order of magnitude larger than what previously observed in close-packed arrays of inorganic QDs (30 nm) [14] and PNCs assemblies (up to 50-70 nm). [15] Here, we expanded our investigation by reporting for the first time a complete spectrally resolved map of the exciton diffusion spot in a similar Colloidal inorganic perovskite nanocrystals (PNCs) are solution-processable optoelectronic materials whose emission can be easily tuned via both size and composition while maintaining high photoluminescence quantum yield. Despite their relative defect tolerance, they suffer from photoinduced damage and degradation under ambient conditions. The lack of long-term stability is addressed by investigating how a ≈3 nm transparent ceramic coating applied onto a thin layer of close-packed PNCs via atomic layer deposition (ALD) affects the exciton mobility across the PNCs. Samples coated via both thermal and plasma ALD are compared, as well as an uncoated one. Exciton diffusion measurements yield a record value for all samples, up to λ D = 480 ± 24 nm, one order of m...

Guidelines for the characterization of metal halide nanocrystals

“…The study of the physical properties of MH NCs is a vivid field of research relying on various continuous-wave and time-resolved optical spectroscopies performed under controlled temperature [55][56][57][58][59][60] and environmental conditions [61][62][63] at both the ensemble and the single-particle level (Figure 4) [64][65][66][67]. This enables us to build a comprehensive photophysical picture including the bandgap energy [20,27], the emission spectrum and its excitonic versus defect/dopantbased contributions [6,[68][69][70][71][72], the exciton [73] and biexciton binding energies [74], and the rates of radiative and nonradiative processes in single NC and ensembles [75][76][77] and in hybrid architectures [78][79][80][81][82], as well as the extent of blinking processes and single-photon emission properties [64][65][66][67] (Figure 4). Overall, this information offers design guidelines for the engineering of perovskite NCs with optical properties tailored for specific applications.…”

All-inorganic lead halide perovskite nanocrystals applied in advanced display devices

“…154 In addition, atomic layer deposition (ALD) is an alternative method to realize the precision thickness control of alumina layer on CsPbBr 3 QDs. 155,156 Besides, SiO 2 /Al 2 O 3 monolith binary coating has been already synthesized on CsPbBr 3 QDs, which decreased the pinhole defects of coating layers beyond the individual coatings of SiO 2 or Al 2 O 3 . 157 Interestingly, monodisperse CsPbX 3 /SiO 2 NCs were successfully prepared by combining a water-triggered transformation process and a sol-gel method.…”

Persistent enhancement of exciton diffusivity in CsPbBr 3 nanocrystal solids

“…CsPbBr 3 NCs are a particularly attractive perovskite morphology due to their bright and stable luminescence (15,30), quantum optical properties (31)(32)(33), and evidence for strong excitonic coupling in NC arrays (34)(35)(36). Initial reports suggest highly mobile excitons within CsPbBr 3 NC solids (7,37,38).…”