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We present the analytic workflow to understand the temperature and illumination-intensity-dependent recombination of the photoinduced charge carriers in organic–inorganic hybrid perovskite solar cells based on methylammonium lead iodide (CH3NH3PbI3) thin films. The temperature-dependent, open-circuit voltage analysis reveals that the recombination of photoinduced charge carriers predominantly occurs at our PEDOT:PSS/CH3NH3PbI3 interface as well as in the depletion region. Taking into account the structural phase transition in CH3NH3PbI3 films, as confirmed using temperature-dependent x-ray diffraction spectra and dielectric constant measurements, the illumination-dependent short-circuit current and open-circuit voltage analysis shows both bimolecular and trap-assisted recombination is dominant in our solution-processed perovskite solar cells. [ABSTRACT FROM AUTHOR]

Junctionless tunneling field-effect transistor (JL-TFET) is an excellent potential alternative to conventional MOSFET and TFET due to the lack of a steep doping profile, which makes it easier to fabricate. JL-TFET not only offers a lower subthreshold swing (SS) compared to MOSFET, but mitigates the low on-current problem associated with conventional TFET. The DC and analog characteristics of JL-TFET can be further improved by design modifications. In this research, we have presented two novel structures of JL-TFET: stimulated n-pocket JL-TFET (SNPJL-TFET) and SNPJL-TFET with heterogeneous gate dielectric. The performance of these devices has been gauged against conventional JL-TFET. Both novel structures exhibit excellent performance including point SS around 20 mV/dec, high ION/IOFF in the order of 1014 and lower threshold voltage (VT). By analyzing RF and linearity parameters such as the transconductance generation factor, FT, transit time, total factor productivity, second-order voltage intercept point, third-order voltage intercept point, third-order input intercept point and third-order intermodulation distortion, it is observed that the proposed devices are more suitable for RF applications since they show superiority in most of the analyzed parameters. [ABSTRACT FROM AUTHOR]

Spectroscopic ellipsometry is a powerful technique for determining optical properties of any thin surface. A method for characterizing optical properties of warm asphalt binder using spectroscopic ellipsometry along with associated results has been presented in this paper. Thin films of warm asphalt binders were produced using LEADCAP and Sasobit and characterized using a variable angle spectroscopic ellipsometry. Refractive index and extinction coefficient of each of the samples (original and aged) were extracted from model fitted spectra. Clear variation in refractive index and extinction coefficient was observed among the samples before and after aging. The samples were found to be highly reflective with refractive index 'n' in the range 1.55–1.62 and extinction coefficient 'k' in the range of 0.01–0.06, both before and after aging. Reflectivity of PG 64-22 with LEADCAP exhibited the highest refractive index and the lowest extinction coefficient in visible wavelength of light among the samples. The results indicated that the highest reflection of visible light can be observed from LEADCAP-modified binder. Cracking properties and absorption coefficient of the binders are observed to have a correlation. The method reported here can be applied to any type of asphalt binder to determine its light absorption and reflection characteristics for a wide range of wavelength. [ABSTRACT FROM AUTHOR]

The rapid surge in perovskite solar cell efficiency has necessitated the development of viable metrology techniques during device integration, paving the way for commercialization. Ellipsometry is considered the most appropriate technique for fast and accurate thickness measurement for large scale production. However, a precise and well-calibrated model is a prerequisite for this technique. While ellipsometry of individual device layers has been reported in recent perovskite literature, a comprehensive multilayer modeling approach is thus far unavailable. Perovskite optoelectronic devices generally consist of a six-layer film stack with three transparent layers required for optical absorption in the perovskite layer. Spin casted thin films, now common in this line of research, impart their own difficulties into ellipsometric modeling. Roughnesses at each heterointerface, similarities in optical spectra of transparent layers, and anomalous dispersion of perovskite are just a few of such challenges. In this work, we report the process of building an ellipsometry model from scratch for thickness measurement of methylammonium lead iodide (MAPI) perovskite and indium tin oxide (ITO)/hole transport layer (HTL) bilayer thin film stacks on a glass substrate. Three promising representatives of HTLs (CuI, Cu2O, and PEDOT:PSS) were studied. The models were extended to measure the individual layer thicknesses of the MAPI/HTL/ITO film stack on a glass substrate using the models developed for individual layers. Optical constants of all the representative thin films were thus extracted for a wide wavelength range (300 nm–900 nm). [ABSTRACT FROM AUTHOR]

Aggressive technology scaling as per Moore’s law has led to elevated power dissipation levels owing to an exponential increase in subthreshold leakage power. Short channel effects (SCEs) due to channel length reduction, gate insulator thickness change, application of high-k gate insulator, and temperature change in a double-gate metal-oxide-semiconductor field-effect transistor (DG MOSFET) and carbon nanotube field-effect transistor (CNTFET) were investigated in this work. Computational simulations were performed to investigate SCEs, viz. the threshold voltage (Vth) roll-off, subthreshold swing (SS), and Ion/Ioff ratio, in the DG MOSFET and CNTFET while reducing the channel length. The CNTFET showed better performance than the DG MOSFET, including near-zero SCEs due to its pure ballistic transport mechanism. We also examined the threshold voltage (Vth), subthreshold swing (SS), and Ion/Ioff ratio of the DG MOSFET and CNTFET with varying gate insulator thickness, gate insulator material, and temperature. Finally, we handpicked almost similar parameters for both the CNTFET and DG MOSFET and carried out performance analysis based on the simulation results. Comparative analysis of the results showed that the CNTFET provides 47.8 times more Ion/Ioff ratio than the DG MOSFET. Its better control over the threshold voltage, near-zero SCEs, high on-current, low leakage power consumption, and ability to operate at high temperature make the CNTFET a viable option for use in enhanced switching applications and low-voltage digital applications in nanoelectronics. [ABSTRACT FROM AUTHOR]

The nucleation and growth of organic–inorganic hybrid perovskite films induced by the molar ratio of precursor components and their role in optoelectronic performance are investigated. Lead iodide (PbI2), methylammonium acetate (MAAc) and methylammonium iodide (MAI) mixed in different ratios were used as starting precursors for active layer deposition. While all the as cast films showed the presence of a precursor intermediate (PbIx·MAAc·MAI), the films derived from 1 : 1 : 1 and 1 : 0.5 : 1 ratios also exhibited crystallization of the perovskite (CH3NH3PbI3) phase during the spin coating process. The nucleation and crystallization of the perovskite phase in films derived from the equimolar precursor ratio were found to be the key to growing larger, smoother and single crystalline grains along the thickness leading to higher carrier lifetimes. Perovskite solar cells fabricated utilizing such a morphology showed a much higher power conversion efficiency irrespective of the active layer thickness. Furthermore, methyl ammonium bromide based perovskite light emitting diodes were also fabricated using the aforementioned equimolar precursor ratio which exhibited superior device performance compared to diodes with active layers derived from other precursor ratios. This work highlights a facile deposition technique and growth mechanism to attain reproducible, low cost and high-performance perovskite optoelectronic devices. [ABSTRACT FROM AUTHOR]

Transparency loss and excess excitation loss are responsible for relatively lower conversion efficiency of single junction solar cell. One way to reduce these two losses is to use multijunction solar cell. In this research InxGa1-xN based single, double and triple junction solar cells were simulated employing AMPS-1D simulator. The band gap of each layer depends on the composition percentage of InN and GaN within InxGa1-xN. In this simulation the authors found 24.51, 33.89, and 42.12% efficiencies for single, double and triple junctions, respectively. [ABSTRACT FROM AUTHOR]