Abstract:In semiconductors, increasing mobility with decreasing temperature is a signature of charge carrier transport through delocalized bands. Here, we show that this behavior can also occur in nanocrystal solids due to temperature-dependent structural transformations. Using a combination of broadband infrared transient absorption spectroscopy and numerical modeling, we investigate the temperature-dependent charge transport properties of well-ordered PbS quantum dot (QD) solids. Contrary to expectations, we observe … Show more
“…The exciton diffusion rate is denoted by k Δ E , and the fitted values are (0.113 ± 0.005) and (0.455 ± 0.055) ns −1 for PeNCs and PeSCAs (Figure 8b,d), respectively. The results show that the PeSCAs possess a much narrower energy state distribution than that of PeNCs, [ 56 ] whereas the exciton diffusion rate of PeSCAs is significantly higher than that of PeNCs. As shown in the schematic diagram in Figure 8e, the bandgaps in the PeSCAs are all close to the theoretical value of the bulk materials’ bandgap with extremely reduced quantum confinement effects (size effect).…”
Directly growing perovskite single crystals on charge carrier transport layers will unravel a promising route for the development of emerging optoelectronic devices. Herein, in situ growth of high‐quality all‐inorganic perovskite (CsPbBr3) single crystal arrays (PeSCAs) on cubic zinc oxide (c‐ZnO) is reported, which is used as an inorganic electron transport layer in optoelectronic devices, via a facile spin‐coating method. The PeSCAs consist of rectangular thin microplatelets of 6–10 µm in length and 2–3 µm in width. The deposited c‐ZnO enables the formation of phase‐pure and highly crystallized cubic perovskites via an epitaxial lattice coherence of (100)CsPbBr3∥(100)c‐ZnO, which is further confirmed by grazing incidence wide‐angle X‐ray scattering. The PeSCAs demonstrate a significant structural stability of 26 days with a 9 days excellent photoluminescence stability in ambient environment, which is much superior to the perovskite nanocrystals (PeNCs). The high crystallinity of the PeSCAs allows for a lower density of trap states, longer carrier lifetimes, and narrower energetic disorder for excitons, which leads to a faster diffusion rate than PeNCs. These results unravel the possibility of creating the interface toward c‐ZnO heterogeneous layer, which is a major step for the realization of a better integration of perovskites and charge carrier transport layers.
“…The exciton diffusion rate is denoted by k Δ E , and the fitted values are (0.113 ± 0.005) and (0.455 ± 0.055) ns −1 for PeNCs and PeSCAs (Figure 8b,d), respectively. The results show that the PeSCAs possess a much narrower energy state distribution than that of PeNCs, [ 56 ] whereas the exciton diffusion rate of PeSCAs is significantly higher than that of PeNCs. As shown in the schematic diagram in Figure 8e, the bandgaps in the PeSCAs are all close to the theoretical value of the bulk materials’ bandgap with extremely reduced quantum confinement effects (size effect).…”
Directly growing perovskite single crystals on charge carrier transport layers will unravel a promising route for the development of emerging optoelectronic devices. Herein, in situ growth of high‐quality all‐inorganic perovskite (CsPbBr3) single crystal arrays (PeSCAs) on cubic zinc oxide (c‐ZnO) is reported, which is used as an inorganic electron transport layer in optoelectronic devices, via a facile spin‐coating method. The PeSCAs consist of rectangular thin microplatelets of 6–10 µm in length and 2–3 µm in width. The deposited c‐ZnO enables the formation of phase‐pure and highly crystallized cubic perovskites via an epitaxial lattice coherence of (100)CsPbBr3∥(100)c‐ZnO, which is further confirmed by grazing incidence wide‐angle X‐ray scattering. The PeSCAs demonstrate a significant structural stability of 26 days with a 9 days excellent photoluminescence stability in ambient environment, which is much superior to the perovskite nanocrystals (PeNCs). The high crystallinity of the PeSCAs allows for a lower density of trap states, longer carrier lifetimes, and narrower energetic disorder for excitons, which leads to a faster diffusion rate than PeNCs. These results unravel the possibility of creating the interface toward c‐ZnO heterogeneous layer, which is a major step for the realization of a better integration of perovskites and charge carrier transport layers.
“…This is due to multiple carriers congregating in the largest QDs and implies that because energy disorder in QD solids leads to enhanced recombination it can be used for optical gain or fast optical switching [114]. Other groups have since improved the Monte Carlo approach used in these initial studies to analyze the nature of charge transport in QD films [115][116][117]. Surface ligands play a strong role as they induce both positional and energetic disorder that lowers the mobility and/or lifetime of photoexcited carriers [71,118].…”
From a niche field over 30 years ago, quantum dots (QDs) have developed into viable materials for many commercial optoelectronic devices. We discuss the advancements in Pb-based QD solar cells (QDSCs) from a viewpoint of the pathways an excited state can take when relaxing back to the ground state. Systematically understanding the fundamental processes occurring in QDs has led to improvements in solar cell efficiency from ~3% to over 13% in 8 years. We compile data from ~200 articles reporting functioning QDSCs to give an overview of the current limitations in the technology. We find that the open circuit voltage limits the device efficiency and propose some strategies for overcoming this limitation.
“…For PbS NC superlattices with thiol ligands a FCC structure is expected for smaller NCs (<3 nm radius) (Fig. 2c) 16 .…”
Section: Resultsmentioning
confidence: 90%
“…This tunability has been used to engineer the electronic and optical structure of NCs, and is recognized as key for a wide array of applications, including LEDs, solar cells and photo-detectors, transistors, phase-change memory, and thermoelectric devices 9–13 . Furthermore, the inter-NC spacing and packing of the NCs into these superlattices can be tuned by the size and shape of the NCs and choice of ligand 1,14 , with structures ranging from primary crystal structures (e.g., cubic 3,15 , BCC 14 , FCC 16 , and hexagonal 2 ) to complex binary systems (e.g., NaCl, MgZn 2 …) 5,17 . This multi-parameter tunability can potentially be exploited to control the collective vibrational structure of the NC superlattice, which would enable the design of new materials via phonon engineering.Fig.…”
Phonon engineering of solids enables the creation of materials with tailored heat-transfer properties, controlled elastic and acoustic vibration propagation, and custom phonon–electron and phonon–photon interactions. These can be leveraged for energy transport, harvesting, or isolation applications and in the creation of novel phonon-based devices, including photoacoustic systems and phonon-communication networks. Here we introduce nanocrystal superlattices as a platform for phonon engineering. Using a combination of inelastic neutron scattering and modeling, we characterize superlattice-phonons in assemblies of colloidal nanocrystals and demonstrate that they can be systematically engineered by tailoring the constituent nanocrystals, their surfaces, and the topology of superlattice. This highlights that phonon engineering can be effectively carried out within nanocrystal-based devices to enhance functionality, and that solution processed nanocrystal assemblies hold promise not only as engineered electronic and optical materials, but also as functional metamaterials with phonon energy and length scales that are unreachable by traditional architectures.
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