Semiconductor Two-Dimensional PdQ2 (Q=S, Se) Monolayer: Strain Modulating Electronic Band Gaps and SQ Efficiencies

We studied the physical, electronic transport and optical properties of a unique pentagonal PdQ2 (Q= S, Se) monolayers. The dynamic stability of 2D - wrinkle like - PdQ2 is proven by positive phonon frequencies in the phonon dispersion curve. The optimized structural parameters of wrinkled pentagonal PdQ2 are in good agreement with the available experimental results. The ultimate tensile strength (UTHS) was calculated and found that, penta-PdS2 monolayer can withstand up to 16% (18%) strain along x (y) direction with 3.44 GPa (3.43 GPa). While, penta-PdSe2 monolayer can withstand up to 17% (19%) strain along x (y) dirrection with 3.46 GPa (3.40 GPa). It is found that, the penta-PdQ2 monolayers has the semiconducting behavior with indirect band gap of 0.94 and 1.26 eV for 2D-PdS2 and 2D-PdSe2, respectively. More interestingly, at room temperacture, the hole mobilty (electron mobility) obtained for 2D-PdS2 and PdSe2 are 67.43 (258.06) cm2 V-1 s-1 and 1518.81 (442.49) cm2 V-1 s-1, respectively. In addition, I-V characteristics of PdSe2 monolayer show strong negative differential conductance (NDC) region near the 3.57 V. The Shockly-Queisser (SQ) effeciency prameters of PdQ2 monolayers are also explored and the highest SQ efficeinciy obtained for PdS2 is 33.93% at -5% strain and for PdSe2 is 33.94% at -2% strain. The penta-PdQ2 exhibits high optical absorption intensity in the UV region, up to 4.04 × 105 (for PdS2) and 5.28 × 105 (for PdSe2), which is suitable for applications in optoelectronic devices. Thus, the ultrathin PdQ2 monolayers could be potential material for next-generation solar-cell applications and high performance nanodevices.

Development of organic–inorganic Halide Perovskites (OHPs) based Memristors

Organic – inorganic halide perovskite (OHP) has drawn researchers’ attention working in the field of optoelectronics from last ten years due to its remarkable optical properties such as adjustable band gap, ambipolar charge transport, high optical absorption coefficients, and extended carrier diffusion lengths. OHP based memristors (memory + resistors) are a newly introduced passive two-terminal, nonlinear device used for information storage. In this work we have fabricated methyl ammonium lead iodide (MAPbI3) crystals-based device from MAPbI3 crystals. The crystals have been developed by simple solution process-based method. Developed crystals have shown highly porous geometry and trap charges across these pores facilitates higher conductivity. The fabricated device exhibits ~2.7 milli second response recovery time, which enabled elevated speed and showed hysteresis in the I-V characteristics thus demonstrating superior storage capacities. Hence, the developed device has been potential tool for next-generation non-volatile memories.

Plasmon-Mediated Oxidation Reaction on Au/p-Cu2O: The Origin of Hot Holes

More sustainable solutions are needed to produce chemicals and fuels, mainly to face rising demands and mitigate climate change. Light, as a reagent, has emerged as a route to activate small molecules, e.g., H2O, CO2, N2, and make complex chemicals in a process called photocatalysis. Several photosystems have been proposed, with plasmonic technology emerging as one the most promising technologies due to its high optical absorption and hot-carrier formation. However, the lifetime of hot carriers is unsuitable for direct use; therefore, they are normally coupled with suitable charge-accepting materials, such as semiconductors. Herein, a system is reported consisting of Au supported in p-Cu2O. The combination of p-Cu2O intrinsic photoactivity with the plasmonic properties of Au extended the system’s optical absorption range, increasing photocatalytic efficiency. More importantly, the system enabled us to study the underlying processes responsible for hot-hole transfer to p-Cu2O. Based on photocatalytic studies, it was concluded that most of the holes involved in aniline photo-oxidation come from hot-carrier injections, not from the PIRET process.

Lateral Structured Phototransistor Based on Mesoscopic Graphene/Perovskite Heterojunctions

Due to their outstanding optical properties and superior charge carrier mobilities, organometal halide perovskites have been widely investigated in photodetection and solar cell areas. In perovskites photodetection devices, their high optical absorption and excellent quantum efficiency contribute to the responsivity, even the specific detectivity. In this work, we developed a lateral phototransistor based on mesoscopic graphene/perovskite heterojunctions. Graphene nanowall shows a porous structure, and the spaces between graphene nanowall are much appropriated for perovskite crystalline to mount in. Hot carriers are excited in perovskite, which is followed by the holes’ transfer to the graphene layer through the interfacial efficiently. Therefore, graphene plays the role of holes’ collecting material and carriers’ transporting channel. This charge transfer process is also verified by the luminescence spectra. We used the hybrid film to build phototransistor, which performed a high responsivity and specific detectivity of 2.0 × 103 A/W and 7.2 × 1010 Jones, respectively. To understand the photoconductive mechanism, the perovskite’s passivation and the graphene photogating effect are proposed to contribute to the device’s performance. This study provides new routes for the application of perovskite film in photodetection.

Optical properties of orthorhombic germanium selenide: an anisotropic layered semiconductor promising for optoelectronic applications

Group-IV monochalcogenides, such as germanium selenide (GeSe) are strongly anisotropic semiconducting van der Waals crystals isoelectronic to black phosphorus, with superior stability in air conditions. High optical absorption, good conductivity,...

Halide perovskites: third generation photovoltaic materials empowered by metavalent bonding

Third-generation photovoltaic (PV) materials combine many advantageous properties, including a high optical absorption together with a large charge carrier mobility, facilitated by small effective masses. Halide perovskites (ABX3, where X = I, Br or Cl) appear to be the most promising third-generation PV materials at present. Their opto-electronic properties are governed by the B-X bond. A quantum-chemical bond analysis reveals that this bond differs significantly from ionic, metallic or covalent bonds. Instead, it is better regarded as metavalent, since it shares approximately one p-electron between adjacent atoms. The resulting s–bond is half-filled, which causes pronounced optical absorption. Electron transfer and lattice distortions open a moderate band gap, resulting in charge carriers with small effective masses. Hence metavalent bonding explains the favorable PV properties of halide perovskites. This is summarized in a map for different bond types, which provides a blueprint to design third-generation PV materials.

A two-dimensional quinazoline based covalent organic framework with a suitable direct gap and superior optical absorption for photovoltaic applications

The suitable band gap and high optical absorption make Q-COF monolayer as an ideal candidate for photovoltaic applications.

Morphological Modification and Analysis of ZnO Nanorods and Their Optical Properties and Polarization

We report on the effect of the morphological modification on optical properties and polarization of ZnO nanorods (NR). Here, the morphology and structure of the ZnO NR were modified by introducing different annealing temperatures. The increase of length and diameter and change in density of the ZnO NR were clearly observed by increasing the annealing temperature. We found that the samples show different oxygen vacancy (VO) and zinc interstitial (ZnI) concentrations. We suggest that the different concentrations of VO and ZnI are originated from morphological and structural modification. Our results reveal that optical absorption and polarization of ZnO NR could be enhanced by producing a high concentration of VO and ZnI. The modification of VO and ZnI promotes a decrease in the band gap and coexistence of high optical absorption and polarization in our ZnO NR. Our findings would give a broad insight into the morphological modification and characterization technique on ZnO NR. The high optical and polarization characteristics of ZnO NR are potential for developing the high-performance nanogenerator device for multitype energy harvesting.

Stable mixed group II (Ca, Sr) and XIV (Ge, Sn) lead-free perovskite solar cells

Novel stable perovskites: Pb in CH3NH3PbI3 is replaced by Ca/(Ge, Sn) or Sr/(Ge, Sn) and exhibits high optical absorption.