Electron–Phonon-Mediated Temperature-Dependent Optical Bandgap of MAPbCl_<i>x</i>Br_3–<i>x</i> Single Crystals

Methylammonium-lead-halide compounds have emerged as promising bandgap engineering materials due to their ability to fine-tune the energy gap through halogen element mixing. We present a comprehensive investigation of the temperature-dependent photoluminescence (PL) transition characteristics exhibited by single crystals of chlorine- and bromine-based methylammonium lead halides. MAPbCl3 and MAPbBr3 crystals exhibit a distinct, sharp, free exciton transition with an abrupt transition behavior associated with the structural phase transition as the temperature varies. However, when the two halogen elements are mixed within the crystals, no structural phase transition is observed. This study explores the temperature-dependent variations in integrated PL intensity, full width at half-maximum, and peak transition energy of the crystals. The obtained results discuss the intricate interplay between temperature, crystal structure, and composition, providing valuable insights into the optical properties and potential applications of organic–inorganic hybrid methylammonium lead halide single crystals as tunable energy gap semiconductor materials

Compliance-Free Multileveled Resistive Switching in a Transparent 2D Perovskite for Neuromorphic Computing

We demonstrate the pulsed voltage tunable multileveled resistive switching (RS) across a promising transparent energy material of (C₄H₉NH₃)₂PbBr₄. The X-ray diffraction and scanning electron microscopy results confirm the growth of (001) plane-orientated nanostructures of (C₄H₉NH₃)₂PbBr₄ with an average size of ∼360 nm. The device depicts optical transmittance higher than 70% in the visible region and efficient absorbance in the ultraviolet region. The current–voltage measurement shows the bipolar RS. In addition, depending on the magnitude of applied electric pulse, the current across the device can be flipped in four different levels, which remain stable for long time, indicating multimode RS. Further, the current across the device increases gradually by applying continuous pulses, similar to the biological synapses. The observed results are attributed to the electric field-induced ionic migration across the (C₄H₉NH₃)₂PbBr₄. The existing study should open a new avenue to apply this promising energy material of perovskite for multifunctional advanced devices

Probing Pathways of Conductive Filaments of FAMAPbI₃ with Controlled FA Composition Using Conductive Atomic Force Microscopy

The characteristics of FAMAPbI3-based write-once-read-many (WORM) devices were controlled by a cation-exchange process as part of a technique to alter the FA composition in FAMAPbI3 films. Interestingly, it was found that an increase in the FA composition in FAMAPbI3 films resulted in a completely inactive WORM device. Such a memory characteristic of a WORM device was attributed to the high iodine vacancy (VI) ion migration energy that prevented the formation of VI conductive filaments (CFs) with the increase in the FA composition in FAMAPbI3 film. By comparing the active and inactive FAMAPbI3 WORM devices, the pathways of CFs within FAMAPbI3 WORM devices were investigated using conductive atomic force microscopy. Our results showed that the CFs were dominantly formed around grain boundaries, while some grain interior regions showed very low conductivity. These studies on the CF formation mechanism provide a better understanding of RS memory characteristics in multication perovskite materials

Interface Trap Suppression and Electron Doping in Van der Waals Materials Using Cross-Linked Poly(vinylpyrrolidone)

The instability of van der Waals (vdW) materials leads to spontaneous morphological and chemical transformations in the air. Although the passivation of vdW materials with other resistive materials is often used to solve stability issues, this passivation layer can block carrier injection and thus interfere with charge transfer doping. In this study, a facile method is proposed for n-doping and mediation of Se vacancies in tungsten diselenide (WSe2) by poly­(vinylpyrrolidone) (PVP) coating. The major carrier type of the PVP-coated WSe2-based field-effect transistor (FET) was converted from hole (p-type) to electron (n-type). Furthermore, the vacancy-induced interface trap density was reduced by approximately 500 times. This study provides a practical doping and passivation method for the van der Waals materials, as well as a comprehensive understanding of the chemical reaction and electronic transport in these materials