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The hysteresis effect is a vital issue in perovskite solar cells that warrants close scrutiny, of which ion migration and the resultant interfacial ion accumulation are widely considered to be the most important origination. However, owing to the lack of specific characterization tools to disentangle the complicated interaction between ions and charge carriers, it is yet unidentified which ionic species govern the hysteresis effect, bringing difficulties in further device optimization. Herein, adopting a home-built circuit-switched transient photoelectric technique, whereby ion migration dynamics can be studied without interference from photogenerated charge carriers, the role of different ions in the photoelectric conversion process is elucidated. As suggested by the experimental results, the hysteresis effect dominantly arises from the migration of organic cations instead of the halide anions and can be well interpreted in terms of the strongly coupled cation–electron pairs. On the basis of these findings, we showcase the effectiveness of suppressing the hysteresis factor by the inhibition of the methylamine cations' migration. The present work can provide targeted and sufficient guidance for the preparation of high-stability and high-efficiency perovskite solar cells.

Polar topologies with exotic textures and functionalities in low-dimensional ferroelectrics are recently drawing extensive attention. Elucidating the mechanical responses caused by the phase transitions under external excitation, especially the torsional response still unclear, is quite significant for the development of ferroelectric actuators. Here, using phase-field simulation, we propose a scheme to produce local torsional force via electric field excitation, namely, the electric torsion effect in a ferroelectric nanodot. The results indicate that the twisting response originating from the structural phase transitions between vortex and helical states is tunable in magnitude and orientation by manipulating the external electric fields. This work provides further insight into the electromechanical response of polar topologies and could be conducive to facilitating the development of torsion-based device applications in ferroelectric nanoelectronics.

Phase-field simulations are performed to study domain structures in (001)-oriented PbZr0.4Ti0.6O3 epitaxial thin films. Temperature-misfit strain phase diagrams of the domain structures are constructed under various depolarization fields by adjusting surface screening conditions and film thickness. We find that the vortex-array state area in the phase diagram enlarges with the decrement of the depolarization field, which is contrary to the general view of depolarization field conductive to vortex formation. Moreover, a strain-mediated ferroelectric failure mechanism is found, wherein the ferroelectric characteristics of an ultrathin film with a thickness of 4 nm completely disappear (Curie temperature drops to 0 K) under the open-circuit condition when the compressive misfit strain drops to −2.69%. The results guide further understanding and manipulation of domain structures in ferroelectric nanomaterials.

All inorganic perovskites are regarded as promising candidates for light-emitting diodes (LEDs) due to their excellent luminescent properties and material stability. However, the film morphology of the perovskite emitting layer has a substantial effect on the device performance of perovskite LEDs (PeLEDs). Herein, we developed a facial method to optimize the film morphology of solution-processed CsPbBr3 films by incorporating a Lewis base of caprylyl sulfobetaine (SB3-10) into the perovskite precursor. The interaction between SB3-10 molecules and metal ions in perovskites could retard the crystallization of the CsPbBr3 film, producing a uniform film with a smooth surface morphology. In addition, the addition of SB3-10 could passivate the defects and traps in the perovskite layer to suppress the nonradiative recombination of the charge carriers. Consequently, the resulting CsPbBr3:SB3-10 based PeLEDs presented a maximum external quantum efficiency of 2.3% with a bright luminance of 23 240 cd m−2 and a maximum current efficiency of 8.45 cd A−1. The finding in this work provides a better understanding of the role of SB3-10 based Lewis base in controlling the surface morphology of the CsPbBr3 films.

Efficient forward stimulated Raman scattering (SRS) was observed along 400-nm femtosecond (fs) laser filaments in water. SRS conversion dominated over self-phase modulation induced continuum generation as the input pulse energy was above 4 μJ (∼30 Pcr), implying that plasma in the aqueous filamentation channel played an important role in compensating for the group velocity walk-off between the pump and Stokes pulses. By overlapping two synchronous fs 400-nm filaments to form plasma grating in water, significant enhancement of SRS conversion was observed. Such a SRS enhancement originated from the ultrahigh plasma density in the intersection region of the preformed plasma grating.

During the growth of CH3NH3PbI3−xClx (MAPbI3−xClx) perovskite films by the two-step inter-diffusion method, the presence of a trace amount of oxygen gas is critical to their physical properties and photovoltaic performance. As the oxygen concentration increases, poor film morphologies and incomplete surface coverage are observed. Moreover, by XRD, Raman scattering, and photoluminescence measurements, we find that MAPbI3−xClx grains become more distorted and the electron-hole recombination rate dramatically increases. Higher oxygen concentration triggers a sharp decrease in the current density and the fill factor of corresponding solar cells, which degrades device performance, on average, from 14.3% to 4.4%. This work proves the importance of controlling the oxygen atmosphere in the fabrication of high-performance perovskite solar cells.

Strong fluorescence emissions from nitrogen monohydride (NH) free radical at 336 nm were observed in air, when water vapor was present in a 400 nm femtosecond laser filament. The generated NH radical is ascribed to chemical reaction between nitrogen and water vapor during laser filamentation. The backscattered fluorescence from NH shows an exponential increase with increasing filament length, indicating amplified spontaneous emission. The fluorescence intensity of NH was found to be linearly dependent on the relative humidity around the filament region, and a record of NH fluorescence detection at 2 m was achieved, which opens up the possibility for remote humidity measurements.

The water vapor fluorescence in air from filaments generated by intense ultrashort Ti:sapphire laser pulses is experimentally studied. The backscattered fluorescence from OH shows an exponential increase with increasing filament length, indicating amplified spontaneous emission. By measuring the intensity inside the filament and the fluorescence intensity of OH, a high degree of nonlinearity is obtained, indicating a highly nonlinear field dissociation of H2O molecule.

Remote terahertz (THz) generation from a two-color femtosecond laser-induced filament in air was experimentally demonstrated. A record of remote THz emission at 16 m was achieved. THz pulse energy more than 250 nJ in the frequency range below 5.5 THz was recorded; this is two orders of magnitude stronger than that from single-color excitation. Back-scattered nitrogen (N2) fluorescence signal remotely measured with a lidar is linearly proportional to the THz emission, which would provide a more practical method to characterize the THz pulses.

The generation of terahertz (THz) emission from a dc-biased two-color femtosecond laser-induced filament in air was systematically investigated. A polarization analysis demonstrated that the THz emission could be the sum of two components: one generated by two-color laser-induced filamentation and the second induced by the external dc electric field. The first component is mostly from four-wave mixing process and a transient transverse electric current under the action of the external dc field could be responsible for the second THz emission.