Specific Influences of Trap States with Distinct Spatial and Energetic Distributions on Ion Migration Dynamics in Metal Halide Perovskites.

Trap state engineering has been widely employed to manipulate the dynamics of ion migration in metal halide perovskites (MHPs), a crucial factor associated with the performance and stability of MHP-based devices. However, the specific roles of different trap states remain poorly understood due to their complicated spatial and energetics distributions. Herein, we propose a methodology for independently regulating the distributions of bulk shallow and surface deep trap states in MHPs.

Unraveling the rapid ion migration in perovskite solar cells by circuit-switched transient photoelectric technique.

Ion migration activated by illumination is a critical factor responsible for the performance decline and stability degradation of perovskite solar cells (PSCs). While ion migration has been widely believed to be much slower than charge transport, recent research suggests that, despite the lack of understanding of the mechanism, it may also be involved in a series of rapid photoelectric responses of PSCs. Here, we report an improved circuit-switched transient photoelectric technique with nanosecond temporal resolution, which enables quantitative characterization of ion migration dynamics in PSCs across a fairly broad time window.

Simultaneously improved photoluminescence, stability, and carrier transport of perovskite nanocrystals by post-synthetic perfluorobutanesulfonic acid treatment.

We report a post-synthetic treatment method based on perfluorobutanesulfonic acid (PFBA) to ameliorate the photophysical performance of perovskite nanocrystals. By virtue of the PFBA treatment, both the photoluminescence efficiency and stability of perovskite quantum dot-based colloidal solutions and the electrical conductivity of their close-packed films are simultaneously improved.

Influence of Two- and Three-Dimensional Engineering on the Trap State Distribution and Photophysical Properties of Lead Halide Perovskite Polycrystals.

Constructing a two- and three-dimensional (2D/3D) heterojunction structure on the surface of a 3D perovskite film, termed 2D/3D engineering, is effective in elevating the stability of perovskite polycrystal-based photovoltaic and photoelectronic devices; however, it remains controversial whether this protocol is favorable or detrimental to the device performance. Here, we prepare a series of 2D/3D perovskite films by post-treating the perovskite polycrystalline film with different concentrations of phenethylammonium iodide (PEAI). Systematic spectroscopy and electrochemical studies illustrate that PEAI can penetrate the 3D perovskite network and eliminate the intrinsic trap states of perovskite polycrystals, while the 2D perovskite nanosheets enriched on the top of the polycrystalline film may introduce additional trap states, which manipulate the photoluminescence performance and dynamics of the as-prepared perovskite films in an opposite manner.

Low-Temperature Preparation of High-Quality Perovskite Polycrystalline Films via Crystallization Kinetics Engineering.

Preparation of lead halide perovskite polycrystalline films at a low annealing temperature is highly restricted by their intrinsically large crystallization activation energy, which hinders the conversion of the precursors/intermediates to perovskites and yields as-prepared polycrystals with tiny grain sizes and terrible crystal quality. Herein, we demonstrate through in-situ, real-time spectroscopic studies that both the nucleation and crystal growth kinetics can be improved without the need for a high annealing temperature by treating the film with thiourea, as accounted for by the reduced activation energy. As a consequence, the thiourea-treated perovskite polycrystalline film exhibits larger grain sizes and greater crystallinity than the untreated one.

Mesoporous TiO layer suppresses ion accumulation in perovskite solar cells.

Ion accumulation in perovskite solar cells can be highly suppressed by a mesoporous TiO layer. This is evidenced by the decrease of the ion-related electrostatic potential with increasing the thickness of the mesoporous layer, accounted for by the electron population in the shallow trap states of the TiO nanocrystals.

Electron transport layer assisted by nickel chloride hexahydrate for open-circuit voltage improvement in MAPbI perovskite solar cells.

SnO is a promising electron transport layer (ETL) material with important applications in planar perovskite solar cells (PSCs). However, electron-hole recombination and charge extraction between SnO and the perovskite layer necessitates further exploration. Nickel chloride hexahydrate (NiCl·6HO) was introduced into the SnO ETL, which significantly increased the power conversion efficiency (PCE) from 15.

Lewis Base Plays a Double-Edged-Sword Role in Trap State Engineering of Perovskite Polycrystals.

We report the double-edged-sword effect of the thiourea (a typical Lewis base) additive for tailoring the trap state distribution of perovskite polycrystalline films. Through the thiourea treatment, the polycrystal grain size is greatly increased because of the reduced crystallization activation energy, which, together with the surface defect passivation, alters the density of the energetically "deep" and "shallow" trap states in a trade-off manner. Based on this finding and further photoelectric and spectral studies, the nonmonotonic dependence of the photoluminescence intensity on the thiourea concentration and the complicated time-resolved photoluminescence behavior are excellently clarified.

Lewis Base-Mediated Perovskite Crystallization as Revealed by In Situ, Real-Time Optical Absorption Spectroscopy.

The strategy of Lewis base modification has been shown to be rather effective in fabricating high-quality perovskite crystals; however, the underlying mechanisms remain controversial owing to the lack of any systematic characterization of the crystallization process. Herein, we report a novel non-invasive optical technique, termed vertical reflection-type in situ, real-time absorption spectroscopy, to investigate the mechanisms of Lewis base-mediated optimization of perovskite crystallinity by visualizing the entire energetic landscape of crystal growth. We show that by virtue of the urea additive, a prototypical Lewis base, the growth kinetics is accelerated prominently by decreasing the activation energy from 73.

Influence of the MACl additive on grain boundaries, trap-state properties, and charge dynamics in perovskite solar cells.

Grain boundary trap passivation in perovskite films has become one of the most effective strategies for suppressing the charge recombination and enhancing the photovoltaic performance of perovskite solar cells, whereas the relevant trap-state properties and the charge carrier dynamics need to be further clarified. In this work, the CH3NH3Cl (MACl) additive is introduced into the MAI:PbI2 precursor solution to obtain perovskite films comprising various grain sizes with distinct grain boundaries and trap-state properties. The influence of grain boundary traps passivated with the MACl additive on trap-state properties and charge carrier transport/recombination dynamics is systematically studied with time-resolved spectroscopic and transient photoelectric characterization.

The influence of the electron transport layer on charge dynamics and trap-state properties in planar perovskite solar cells.

Despite the outstanding photovoltaic performance of perovskite solar cells, the correlation between the electron transport layer and the mechanism of photoelectric conversion is still not fully understood. In this paper, the relationship between photovoltaic performance and carrier dynamics is systematically studied in both TiO- and SnO-based planar perovskite devices. It is found that the different electron transport layers result in distinct forward scan results and charge dynamics.

Modification of NiO hole transport layer for acceleration of charge extraction in inverted perovskite solar cells.

The modification of the inorganic hole transport layer has been an efficient method for optimizing the performance of inverted perovskite solar cells. In this work, we propose a facile modification of a compact NiO film with NiO nanoparticles and explore the effects on the charge carrier dynamic behaviors and photovoltaic performance of inverted perovskite devices. The modification of the NiO hole transport layer can not only enlarge the surface area and infiltration ability, but also adjust the valence band maximum to well match that of perovskite.

Concentration-regulated photon upconversion and quenching in NaYF:Yb,Er nanocrystals: nonexponentiality revisited.

Concentration quenching of rare-earth doped upconversion nanoparticles severely limits the dopant concentration, and this greatly hinders their potential applications. Therefore, it is necessary to understand the roles of dopant concentration in photon population and luminescence quenching for materials designed with improved upconversion luminescence (UCL). Herein, the excited-state dynamics of well-accepted NaYF4:Yb3+,Er3+ nanocrystals were investigated as models based on the Kohlrausch-function.

Charge carrier recombination dynamics in a bi-cationic perovskite solar cell.

The compositional engineering is of great importance to tune the electrical and optical properties of perovskite and improve the photovoltaic performance of perovskite solar cells. The exploration of the corresponding photoelectric conversion processes, especially the carrier recombination dynamics, will contribute to the optimization of the devices. In this work, perovskite with mixed methylammonium (MA) and formamidinium (FA) as organic cations, MA0.

Naturally occurring nanotube with surface modification as biocompatible, target-specific nanocarrier for cancer phototherapy.

Phototherapy has drawn increasing attention including the use of nanocarriers with high drug loading capacity and delivery efficacy for target-specific therapy. We have made use of naturally-occurring halloysite nanotubes (HNTs) to build a biomimetic nanocarrier platform for target-specific delivery of phototherapeutic agents. The HNTs were decorated with poly(sodium-p-styrenesulfonate) (PSS) to enhance the biocompatibility, and were further functionalized by lumen loading the type-II photosensitizer indocyanine green (ICG).

Energy transfer mechanism dominated by the doping location of activators in rare-earth upconversion nanoparticles.

Research on the energy transfer mechanism of rare-earth-doped upconversion nanoparticles (UCNPs) has been an important area due to the increasing demand for tuning multicolor emission and enhancing the upconversion efficiency; however, because of large energy mismatch, many lanthanide activators, such as Eu3+, cannot realize highly efficient near infrared-to-visible upconversion by simple codoping of Yb3+. Therefore, introduction of other ions to assist the energy transfer process is required. Herein, we prepared core-shell nanoparticles with different doping locations to investigate the upconversion energy transfer mechanism.

Characterization of the influences of morphology on the intrinsic properties of perovskite films by temperature-dependent and time-resolved spectroscopies.

Organic-inorganic halide perovskites have attracted enormous attention owing to their promising application in photovoltaic devices. The morphology of the perovskites is the key to driving the performance of perovskite devices, which necessitates a systematic study. In this work, two typical morphologies, i.

Integrity of Membrane Structures in Giant Unilamellar Vesicles as Assay for Antioxidants and Prooxidants.

We have attempted to evaluate, on the basis of optical microscopy for a single giant unilamellar vesicle (GUV), the potency of antioxidants in protecting GUV membranes from oxidative destruction. Photosensitized membrane budding of GUVs prepared from soybean phosphatidylcholine with chlorophyll a (Chl a) and β-carotene (β-Car) as photosensitizer and protector, respectively, were followed by microscopic imaging. A dimensionless entropy parameter, ΔE, as derived from the time-resolved microscopic images, was employed to describe the evolution of morphological variation of GUVs.

Multiple-Trapping Model for the Charge Recombination Dynamics in Mesoporous-Structured Perovskite Solar Cells.

The photovoltaic performance of organic-inorganic hybrid perovskite solar cells has reached a bottleneck after rapid development in last few years. Further breakthrough in this field requires deeper understanding of the underlying mechanism of the photoelectric conversion process in the device, especially the dynamics of charge-carrier recombination. Originating from dye-sensitized solar cells (DSSCs), mesoporous-structured perovskite solar cells (MPSCs) have shown many similarities to DSSCs with respect to their photoelectric dynamics.

Design and Fabrication of Temperature-Sensitive Nanogels with Controlled Drug Release Properties for Enhanced Photothermal Sterilization.

For better removal of excessive free radicals and harmful bacteria from the human body, the development of synergistic antioxidant and antibacterial agents is urgently required. Herein, we designed novel temperature-sensitive, curcumin (Cur)-loaded nanogels for the application of scavenging reactive oxygen species and killing pathogenic bacteria. Photothermal sterilization, different from traditional antibiotics, is a promising and effective treatment for pathogenic bacterial infection.

Power output and carrier dynamics studies of perovskite solar cells under working conditions.

Perovskite solar cells have emerged as promising photovoltaic systems with superb power conversion efficiency. For the practical application of perovskite devices, the greatest concerns are the power output density and the related dynamics under working conditions. In this study, the working conditions of planar and mesoscopic perovskite solar cells are simulated and the power output density evolutions with the working voltage are highlighted.

DNA-assisted upconversion nanoplatform for imaging-guided synergistic therapy and laser-switchable drug detoxification.

The side effects of chemotherapy bring significant physical and psychological suffering to patients. To solve this urgent medical problem, Yb and Er co-doped NaLuF upconversion nanoparticles (UCNPs) were constructed for upconversion luminescence (UCL)-labeled diagnosis under 980 nm laser irradiation. The UCNPs were then modified layer by layer with polypyrrole and a special programming DNA segment as photothermal conversion agents and controllable drug carriers, respectively.

Adverse Effects of Excess Residual PbI on Photovoltaic Performance, Charge Separation, and Trap-State Properties in Mesoporous Structured Perovskite Solar Cells.

Organic-inorganic halide perovskite solar cells have rapidly come to prominence in the photovoltaic field. In this context, CH NH PbI , as the most widely adopted active layer, has been attracting great attention. Generally, in a CH NH PbI layer, unreacted PbI inevitably coexists with the perovskite crystals, especially following a two-step fabrication process.