Solvothermal synthesis of TiO2nanospheres for non-volatile memory and synaptic learning applications.

In this study, we used the one-pot solvothermal method to synthesize the TiO2nanospheres (NSs) and used them for non-volatile memory and neuromorphic computing applications. Several analytical tools were used to understand the structural, optical, morphological, and compositional characteristics of synthesized TiO2NSs. The tetragonal crystal structure of anatase TiO2was formed, according to the Rietveld refined x-ray diffraction results. The NS morphology was confirmed by field emission scanning electron microscopy and transmission electron microscopy images. X-ray photoelectron spectroscopy was probed to understand the elemental composition and electronic states of the TiO2NSs. We specifically looked at the impact of reaction time on the structural, optical, morphological, compositional, and resistive switching (RS) properties of TiO2NSs. The fabricated devices (Ag/TiO2NSs/FTO) exhibit bipolar RS behavior. The optimized RS device shows good endurance (5000 cycles) and memory retention (5000 s) properties. Moreover, fabricated devices showed double-valued charge-flux characteristics, whereas charge transport was caused by the Ohmic and space charge-limited current mechanisms. Additionally, the optimized device can mimic various synaptic characteristics including potentiation-depression, excitatory post-synaptic current, and paired-pulse facilitation.

Eco-friendly MA3Bi2I9perovskite thin films based ammonia sensor.

Organic-inorganic perovskite halides (OIPH) have emerged as a wonder material with growing interest in sensors detecting various toxic gases. However, lead toxicity represents a potential obstacle, and therefore finding lead-free cost-effective compatible materials for gas sensing applications is essential. In this work, methylammonium bismuth iodide i.e. (CH3NH3)3Bi2I9(MABI) perovskite thin films-based ammonia (NH3) sensor was synthesized using an antisolvent-assisted one-step spin coating method. The MABI sensor shows a linear relationship between the responsivity and concentration of NH3with excellent reversibility, high gas responsivity, and humidity stability. The MABI thin-film sensor exhibits a maximum gas response of 24%, a short response/recovery time i.e. 0.14 s /8.15 s and good reversibility at 6 ppm of NH3. It was observed that MABI thin films based sensors have excellent ambient stability over a couple of months. This work reveals that it is feasible to design high-performance gas sensors based on environmentally-friendly Bi-based OIPH materials.

In2O3 nanocapsules for rapid photodegradation of crystal violet dye under sunlight.

We report, a shape controlled novel synthesis of Indium oxide (In2O3) nanocapsule using biogenic reflux method. The In2O3 samples were obtained through optimization of the concentration of sodium citrate, which played a significant role to tune the size of nanocapsules. All synthesized In2O3 samples were characterized by using X-ray diffraction (XRD), infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and selected area electron diffraction (SAED). The morphological study reflects the effect of sodium citrate on the size of nanocapsules and confirms the formation of nanocapsules in the range of 50 nm. Furthermore, the photocatalytic activity of In2O3 nanocapsules based photocatalyst was carried out for the degradation of Crystal Violet (CV) dye under natural sunlight illumination. The experiment revealed that the In2O3 nanocapsule efficiently degrades 90% of CV within 180 min. This effort recommends the synthesis of In2O3 nanocapsule based photocatalyst for rapid degradation of CV under natural sunlight illumination.

Overcoming the Ambient Manufacturability-Scalability-Performance Bottleneck in Colloidal Quantum Dot Photovoltaics.

Colloidal quantum dot (CQD) solar cells have risen rapidly in performance; however, their low-cost fabrication under realistic ambient conditions remains elusive. This study uncovers that humid environments curtail the power conversion efficiency (PCE) of solar cells by preventing the needed oxygen doping of the hole transporter during ambient fabrication. A simple oxygen-doping step enabling ambient manufacturing irrespective of seasonal humidity variations is devised. Solar cells with PCE > 10% are printed under high humidity at industrially viable speeds. The devices use a tiny fraction of the ink typically needed and are air stable over a year. The humidity-resilient fabrication of efficient CQD solar cells breaks a long-standing compromise, which should accelerate commercialization.

Effects of High Temperature and Thermal Cycling on the Performance of Perovskite Solar Cells: Acceleration of Charge Recombination and Deterioration of Charge Extraction.

In this work, we investigated the effects of high operating temperature and thermal cycling on the photovoltaic (PV) performance of perovskite solar cells (PSCs) with a typical mesostructured (m)-TiO2-CH3NH3PbI3-xClx-spiro-OMeTAD architecture. After temperature-dependent grazing-incidence wide-angle X-ray scattering, in situ X-ray diffraction, and optical absorption experiments were carried out, the thermal durability of PSCs was tested by subjecting the devices to repetitive heating to 70 °C and cooling to room temperature (20 °C). An unexpected regenerative effect was observed after the first thermal cycle; the average power conversion efficiency (PCE) increased by approximately 10% in reference to the as-prepared device. This increase of PCE was attributed to the heating-induced improvement of the crystallinity and p doping in the hole transporter, spiro-OMeTAD, which promotes the efficient extraction of photogenerated carriers. However, further thermal cycles produced a detrimental effect on the PV performance of PSCs, with the short-circuit current and fill factor degrading faster than the open-circuit voltage. Similarly, the PV performance of PSCs degraded at high operation temperatures; both the short-circuit current and open-circuit voltage decreased with increasing temperature, but the temperature-dependent trend of the fill factor was the opposite. Our impedance spectroscopy analysis revealed a monotonous increase of the charge-transfer resistance and a concurrent decrease of the charge-recombination resistance with increasing temperature, indicating a high recombination of charge carriers. Our results revealed that both thermal cycling and high temperatures produce irreversible detrimental effects on the PSC performance because of the deteriorated interfacial photocarrier extraction. The present findings suggest that the development of robust charge transporters and proper interface engineering are critical for the deployment of perovskite PVs in harsh thermal environments.

Hybrid Perovskite Thin-Film Photovoltaics: In Situ Diagnostics and Importance of the Precursor Solvate Phases.

Solution-processed hybrid perovskite semiconductors attract a great deal of attention, but little is known about their formation process. The one-step spin-coating process of perovskites is investigated in situ, revealing that thin-film formation is mediated by solid-state precursor solvates and their nature. The stability of these intermediate phases directly impacts the quality and reproducibility of thermally converted perovskite films and their photovoltaic performance.

Fast Crystallization and Improved Stability of Perovskite Solar Cells with Zn2SnO4 Electron Transporting Layer: Interface Matters.

Here we report that mesoporous ternary oxide Zn2SnO4 can significantly promotes the crystallization of hybrid perovskite layers and serves as an efficient electron transporting material in perovskite solar cells. Such devices exhibit an energy conversion efficiency of 13.34%, which is even higher than that achieved with the commonly used TiO2 in the similar experimental conditions (9.1%). Simple one-step spin coating of CH3NH3PbI3-xClx on Zn2SnO4 is found to lead to rapidly crystallized bilayer perovskite structure without any solvent engineering. Furthermore, ultrafast transient absorption measurement reveals efficient charge transfer at the Zn2SnO4/perovskite interface. Most importantly, solar cells with Zn2SnO4 as the electron-transporting material exhibit negligible electrical hysteresis and exceptionally high stability without encapsulation for over one month. Besides underscoring Zn2SnO4 as a highly promising electron transporting material for perovskite solar cells, our results demonstrate the significant role of interfaces on improving the perovskite crystallization and photovoltaic performance.

Ambipolar solution-processed hybrid perovskite phototransistors.

Organolead halide perovskites have attracted substantial attention because of their excellent physical properties, which enable them to serve as the active material in emerging hybrid solid-state solar cells. Here we investigate the phototransistors based on hybrid perovskite films and provide direct evidence for their superior carrier transport property with ambipolar characteristics. The field-effect mobilities for triiodide perovskites at room temperature are measured as 0.18 (0.17) cm(2) V(-1) s(-1) for holes (electrons), which increase to 1.24 (1.01) cm(2) V(-1) s(-1) for mixed-halide perovskites. The photoresponsivity of our hybrid perovskite devices reaches 320 A W(-1), which is among the largest values reported for phototransistors. Importantly, the phototransistors exhibit an ultrafast photoresponse speed of less than 10 µs. The solution-based process and excellent device performance strongly underscore hybrid perovskites as promising material candidates for photoelectronic applications.

CH3NH3PbCl3 Single Crystals: Inverse Temperature Crystallization and Visible-Blind UV-Photodetector.

Single crystals of hybrid perovskites have shown remarkably improved physical properties compared to their polycrystalline film counterparts, underscoring their importance in the further development of advanced semiconductor devices. Here we present a new method of growing sizable CH3NH3PbCl3 single crystals based on the retrograde solubility behavior of hybrid perovskites. We show, for the first time, the energy band structure, charge recombination, and transport properties of CH3NH3PbCl3 single crystals. These crystals exhibit trap-state density, charge carrier concentration, mobility, and diffusion length comparable with the best quality crystals of methylammonium lead iodide or bromide perovskites reported so far. The high quality of the crystal along with its suitable optical band gap enabled us to build an efficient visible-blind UV-photodetector, demonstrating its potential in optoelectronic applications.