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Defect accumulation and nonradiative recombination at the interface of the electron-transport layer (ETL) and the photosensitive layer are inevitable obstacles to efficient and stable perovskite solar cells (PSCs). Herein, we reported a dual-effect interface modification strategy that employs potassium tetrafluoroborate (KBF

The inorganic perovskite solar cells (PSCs) are now playing an increasingly essential role in the realm of clean energy. However, the application of inorganic perovskite solar cells is usually limited as the spontaneous phase transform. Here, we applied the 1H, 1H-Perfluorooctylammonium iodide (PFOAI) upon the surface of the cesium lead iodide (CsPbI3) films by taking advantage of its excellent defect passivation ability and hydrophobicity. Decreased recombination upon the surface and postponed degradation of the device were achieved for the observation of lower trap density and longer carrier lifetime and better stability based on the PFOAI-CsPbI3 films. The champion PFOAI-CsPbI3 based device showed an increased power conversion efficiency (PCE) of 18.24% with the excellent fill factor (FF) of 81.77% and Jsc of 20.51 mA cm−2 and remain ∼85% of its initial PCE for 1000 h (25 °C) in the N2 glovebox. This work adds slightly weight on the balance of balancing the stability and high efficiency of the inorganic PSCs.

Accurate measurements of semiconductor nanocrystal (NC) emission quantum yields (QYs) are critical to condensed phase optical refrigeration. Of particular relevance to measuring NC QYs is a longstanding debate as to whether an excitation energy-dependent (EED) QY exists. Various reports indicate existence of NC EED QYs, suggesting that the phenomenon is linked to specific ensemble properties. We therefore investigate here the existence of EED QYs in two NC systems (CsPbBr3 and CdSe) that are possible candidates for use in optical refrigeration. The influence of NC size, size-distribution, surface ligand, and as-made emission QYs are investigated. Existence of EED QYs is assessed using two approaches (an absolute approach using an integrating sphere and a relative approach involving excitation spectroscopy). Altogether, our results show no evidence of EED QYs across samples. This suggests that parameters beyond those mentioned above are responsible for observations of NC EED QYs.

Cesium lead halide perovskite nanocrystals (PNCs), while possessing facile chemical synthesis routes and high photoluminescence (PL) properties, are still challenged by issues of instability and de...

Semiconductor nanocrystals (NCs) are potential materials for verifiable demonstrations of semiconductor-based laser cooling. The key feature that makes NCs appealing for laser cooling is their near unity emission quantum yields (QYs). An unresolved issue regarding NC QYs, however, centers on the existence of an excitation energy dependent (EED) QY. Here, we study EED QYs on three NC systems, aimed at demonstrating NC-based laser cooling (CsPbBr3, CsPbI3, and CdSe/CdS core/shell NCs). We evaluate the impact of EED QYs using two approaches. The first involves direct QY measurements using an integrating sphere. The second entails photoluminescence excitation spectroscopy where changes to NC QYs with excitation energy can be assessed qualitatively.

Cesium lead halide perovskite nanocrystals (PNCs), while possessing facile chemical synthesis routes and high photoluminescence (PL) properties, are still challenged by issues of instability and degradation. Although atomic layer deposition (ALD) of metal oxides has been one of the common encapsulation approaches for longer term stability, its application inevitably resulted in severe loss of emission efficiency and at times partial loss of structural integrity of perovskites, creating a bottleneck in its practical viability. We demonstrate a nondestructive modified gas-phase technique with codeposition of both precursors trimethylaluminum and water to dramatically enhance the PL emission in zero-dimensional (0D) Cs

Hafnium-oxide-based materials are considered a promising candidate for next-generation nonvolatile memory devices owing to their good CMOS compatibility and robust ferroelectricity at the nanoscale. In this work, we synthesize highly (111)-oriented La-doped HfO2 (HLO) ferroelectric thin films via pulsed laser deposition. Furthermore, the effect of La dopant concentration, thickness, and growth temperature on the ferroelectricity of HLO films is investigated in detail. A maximum remnant polarization of ∼9 μC/cm2 is achieved for only the 5-nm-thick 3 mol. % HLO films without a wake-up process. The 180° inversion of the domain, the butterfly-shaped capacitance–voltage curve, and typical ferroelectric displacement current curve further demonstrate the robust ferroelectricity at the nanoscale. Moreover, the phase evolves from the monoclinic to the orthorhombic and subsequently to the cubic phase with increasing La concentration, which is due to the combined action of oxygen vacancy, epitaxial strain, and chemical pressure. Additionally, in the interface configuration of HLO/La0.7Sr0.3MnO3 (LSMO), the MnO20.7− layer is substituted by the HLO layer on the MnO2-terminated surface of LSMO, which can be attributed to the fact that the HLO layer with higher electronegativity replaces the MnO20.7− layer with the same electronegativity in the HLO film. Therefore, this study provides a reliable pathway for directly obtaining a lightly doped HLO ferroelectric thin film, which can help to broaden the understanding of the ferroelectric physical mechanisms with element doping.

Managing deposition of multilayered nanocrystal quantum dot (NQD) thin films is crucial for future photonic devices to maximize solar energy extraction efficiency. Solution-based NQD deposition methods require additional protection to achieve a discrete layered structure and to prevent optical degradation during processing. An attractive method to passivate and protect NQD films is overcoating with metal oxides, usually grown using atomic layer deposition (ALD). However, a significant quenching of NQD photoluminescence (PL) is typically observed after encapsulation, hindering performance and applicability. Here, we demonstrate a modified gas-phase deposition technique that fully passivates NQD assemblies and, in contrast to standard ALD, maintains PL properties. Combined in situ FTIR and ex situ XPS measurements reveal that upon Al2O3 deposition by ALD, the metal precursor trimethylaluminum (TMA) interacts with oleic acid-capped CdSe–CdS–ZnS core–shell-shell NQDs by reorganizing the ligands and replacing ...

Cesium lead halide perovskite materials have attracted considerable attention for potential applications in lasers, light-emitting diodes, and photodetectors. Here, we provide the experimental and theoretical evidence for photon recycling in CsPbBr3 perovskite microwires. Using two-photon excitation, we recorded photoluminescence (PL) lifetimes and emission spectra as a function of the lateral distance between PL excitation and collection positions along the microwire, with separations exceeding 100 μm. At longer separations, the PL spectrum develops a red-shifted emission peak accompanied by an appearance of well-resolved rise times in the PL kinetics. We developed quantitative modeling that accounts for bimolecular recombination and photon recycling within the microwire waveguide and is sufficient to account for the observed decay modifications. It relies on a high radiative efficiency in CsPbBr3 perovskite microwires and provides crucial information about the potential impact of photon recycling and wa...

We demonstrate enhancement of the photoluminescence (PL) properties of individual zero-dimensional (0D) Cs4PbBr6 perovskite nanocrystals (PNCs) upon encapsulation by alumina using an appropriately ...

It is a daunting challenge to measure the concentration of each component in natural gas, because different components in mixed gas have cross-sensitivity for a single sensor. We have developed a mixed gas identification device based on a neural network algorithm, which can be used for the online detection of natural gas. The neural network technology is used to eliminate the cross-sensitivity of mixed gases to each sensor, in order to accurately recognize the concentrations of methane, ethane and propane, respectively. The neural network algorithm is implemented by a Field-Programmable Gate Array (FPGA) in the device, which has the advantages of small size and fast response. FPGAs take advantage of parallel computing and greatly speed up the computational process of neural networks. Within the range of 0&ndash, 100% of methane, the test error for methane and heavy alkanes such as ethane and propane is less than 0.5%, and the response speed is several seconds.

Observation of energy transfer (ET) from multiexcitonic (MX) complexes in nanocrystal quantum dots (NQDs) has been severely restricted due to efficient nonradiative Auger recombination leading to very low MX emission quantum yields. Here we employed "giant" CdSe/CdS NQDs with suppressed Auger recombination to study ET of biexcitons (BX) and charged excitons (trions) into Si substrate. Photoluminescence (PL) measurements of (sub)monolayers of gNQDs controllably assembled on various interacting surfaces and augmented by single gNQD's imaging reveal appearance of BX spectral signatures and progressive acceleration of PL lifetimes of all excitonic species on Si substrates. From statistical analysis of a large number of PL lifetime traces, representative exciton, trion and BX ET efficiencies are measured as ∼75%, 55% and 45% respectively. Detailed analysis of the MX's radiative rates demonstrate the crucial role of the radiative (waveguide) ET in maintaining high overall transfer efficiency despite the prevalent Auger recombination. Our observations point towards practical utilization of MX-bearing nanocrystals in future optoelectronics architectures.

Single-layer light-emitting electrochemical cells from ionic transition metal complexes (iTMCs) are relatively simple to construct and have great potential as cost effective emissive devices. Most studies to date have focused on iTMC devices from ruthenium and iridium chromophores. For practical applications, thermal stability is important for environmental robustness, and little has been said about their relative thermal stability. Here, we studied the device performance of iridium and ruthenium iTMCs with temperature to directly compare their stabilities. The thermal onset of radiant flux loss is found to be 67 °C (152 °F) for iridium devices, 45 °C higher than ruthenium iTMCs, a show of their superior thermal stability. We subsequently used temperature-dependent electrochemical impedance spectroscopy, temperature-dependent photoluminescence spectroscopy, time resolved photoluminescence spectroscopy, and photoluminescence quantum yield measurements to understand the physical origin of this substantial temperature stability difference. Prior postulates suggested that films from iridium complexes would yield better thermal stability than those from ruthenium complexes due to details of the orbital energetics. Instead, it is found that this superiority is owed to the details of kinetic effects—the competing kinetics of multiple recombination pathways and the relative rates of radiative to nonradiative processes. Such information guides the design of iTMC emitters for superior light-emitting electrochemical cells.

We investigate nonradiative energy transfer (NRET) between CdSe/CdS core/shell “giant” nanocrystal quantum dots (gNQDs) and monolayer domains of molybdenum disulfide (MoS2) grown by chemical vapor deposition. We employ three sets of gNQDs with varied core/shell parameters that exhibit radiative emission from neutral and charged excitons (trions) at different spectral positions from 590 to 660 nm as confirmed by photon statistics of individual nanocrystals. Strong photoluminescence (PL) emission quenching is observed for the donor gNQDs placed on MoS2 domains, indicative of the efficient NRET. Analysis of the double-component PL decays reveals NRET from both neutral excitons and charged trions with the same efficiency. Applying a macroscopic electrodynamics model for the decay of electric-dipole emitters in the vicinity of an ultrathin semiconducting layer with a strong in-plane excitonic polarizability, we confirm high NRET efficiencies from >95% to 85% for dots with diameters from 10 to 20 nm. This demon...

Nonradiative Auger recombination is the primary exciton loss mechanism in colloidal nanocrystals and an impediment for prospective optoelectronic applications. Recent development of new core/shell nanocrystals with suppressed Auger recombination rates has opened the possibility for studying multicarrier states using time-resolved photoluminescence (PL) spectroscopy. An important aspect not addressed in previous works is the scaling of radiative and nonradiative decay rates with the increasing number and type of excitons in individual nanocrystals. Here we conduct extensive single-dot PL spectroscopy of emissive states in PL blinking trajectories of giant silica-coated CdSe/CdS nanocrystals. At low fluences, we observe the appearance of neutral and charged exciton (trion) states. Both negative and positive trions show strongly suppressed Auger recombination rates resulting in PL quantum yields close to 50%. At higher excitation powers, we observe consecutive emergence of lower efficiency states, indicative...

Two-dimensional transition metal dichalcogenides (TMDCs) like MoS2 are promising candidates for various optoelectronic applications. The typical photoluminescence (PL) of monolayer MoS2 is however known to suffer very low quantum yields. We demonstrate a 10-fold increase of MoS2 excitonic PL enabled by nonradiative energy transfer (NRET) from adjacent nanocrystal quantum dot (NQD) films. The understanding of this effect is facilitated by our application of transient absorption (TA) spectroscopy to monitor the energy influx into the monolayer MoS2 in the process of ET from photoexcited CdSe/ZnS nanocrystals. In contrast to PL spectroscopy, TA can detect even non-emissive excitons, and we register an order of magnitude enhancement of the MoS2 excitonic TA signatures in hybrids with NQDs. The appearance of ET-induced nanosecond-scale kinetics in TA features is consistent with PL dynamics of energy-accepting MoS2 and PL quenching data of the energy-donating NQDs. The observed enhancement is attributed to the reduction of recombination losses for excitons gradually transferred into MoS2 under quasi-resonant conditions as compared with their direct photoproduction. The TA and PL data clearly illustrate the efficacy of MoS2 and likely other TMDC materials as energy acceptors and the possibility of their practical utilization in NRET-coupled hybrid nanostructures.

Two-dimensional transition metal dichalcogenides (TMDCs) like MoS2 are promising candidates for various optoelectronic applications. The typical photoluminescence (PL) of monolayer MoS2 is however known to suffer very low quantum yields. We demonstrate a 10-fold increase of MoS2 excitonic PL enabled by nonradiative energy transfer (NRET) from adjacent nanocrystal quantum dot (NQD) films. The understanding of this effect is facilitated by our application of transient absorption (TA) spectroscopy to monitor the energy influx into the monolayer MoS2 in the process of ET from photoexcited CdSe/ZnS nanocrystals. In contrast to PL spectroscopy, TA can detect even non-emissive excitons, and we register an order of magnitude enhancement of the MoS2 excitonic TA signatures in hybrids with NQDs. The appearance of ET-induced nanosecond-scale kinetics in TA features is consistent with PL dynamics of energy-accepting MoS2 and PL quenching data of the energy-donating NQDs. The observed enhancement is attributed to the reduction of recombination losses for excitons gradually transferred into MoS2 under quasi-resonant conditions as compared with their direct photoproduction. The TA and PL data clearly illustrate the efficacy of MoS2 and likely other TMDC materials as energy acceptors and the possibility of their practical utilization in NRET-coupled hybrid nanostructures.

The effects of buoyancy forces on the displacement of one liquid by another in a consolidated porous medium have been investigated experimentally for the specific case in which the two liquids are completely miscible. In order to obtain a clear understanding of the favorable and unfavorable effects of buoyancy forces, experiments were carried out in three different flow modes, namely horizontal, vertical-downward and vertical-upward. As the effects of buoyancy forces are negligible for two-dimensional porous media in the horizontal flow mode, the results obtained in this mode were used as a reference for comparison with those obtained in the two vertical modes. The miscible system employed consisted of an aqueous glycerol solution and distilled water (dyed with methylene blue) as the displaced and displacing fluids respectively. Displacements using five different density ratios were studied, with the density ratio being varied by changing the concentration of the glycerol solution. The breakthrough time and fractional recovery of the displaced fluid were measured in each case and photographs of the unstable fingering patterns were taken for a wide range of injection flow rates. The results obtained indicate that the effects of buoyancy forces can be very significant, especially at low flow rates and/or at high density ratios. When the density of the displacing fluid is less than that of the displaced fluid (which was the case in the present work), buoyancy forces play a deleterious role in vertical-upward displacements since they tend to promote fingering and reduce breakthrough times, thereby producing low recoveries of the displaced phase. In contrast, under the same density conditions, buoyancy forces play a positive role in vertical-downward displacements since they then tend to stabilize the displacement process (i.e. reduce fingering), thereby producing increased breakthrough times and correspondingly high recoveries of the displaced phase. However, at high flow rates, the observed fingering patterns and recoveries are very similar for horizontal, vertical-downward, and vertical-upward displacements, since viscous forces are dominant under such conditions and buoyancy forces are insignificant.