Search

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]

Organohalide lead (hybrid) perovskites have emerged as competitive semiconducting materials for photovoltaic devices due to their high performance and low cost. To further the understanding and optimization of these materials, solution-based methods for interrogating and modifying perovskite thin films are needed. In this work, we report a hydrofluoroether (HFE) solvent-based electrolyte for electrochemical processing and characterization of organic-inorganic trihalide lead perovskite thin films. Organic perovskite films are soluble in most of the polar organic solvents, and thus until now, they were not considered suitable for electrochemical processing. We have enabled electrochemical characterization and demonstrated a processing toolset for these materials utilizing highly fluorinated electrolytes based on a HFE solvent. Our results show that chemically orthogonal electrolytes based on HFE solvents do not dissolve organic perovskite films and thus allow electrochemical characterization of the electronic structure, investigation of charge transport properties, and potential electrochemical doping of the films with in situ diagnostic capabilities. [ABSTRACT FROM AUTHOR]

Despite the recent increase in PPDT2FBT polymer thin film applications for optoelectronic devices, a comprehensive study of this material's optical dispersion properties is unavailable. The optical properties of the PPDT2FBT thin film is investigated using variable-angle spectroscopic ellipsometry (VASE) at ambient conditions. Knowledge of optical dispersion properties is essential for designing and fabricating optoelectronic devices such as solar cells, photodetectors, and photodiodes. In this research, we determined the dielectric function of PPDT2FBT thin film using the B-spline model and then reproduced the dielectric function using Psemi-Tri oscillators. We estimated the refractive index (n) of the thin film to be between 2.00 and 2.15 and the extinction coefficient (k) to be in the range of 1.14–1.39 at a wavelength of 632.8 nm. We further verified the estimated optical properties from the model using directly measured quantities such as transmission and absorption data obtained using the ultraviolet–visible (UV–Vis) spectrometer and thicknesses obtained using a surface profilometer. In addition, we determined the optical band gap of PPDT2FBT using the absorption coefficient. • The optical properties such as n, k of the PPDT2FBT polymer thin film are determined. • It was determined in a nondestructive way using variable-angle spectroscopic ellipsometry at ambient conditions. • We applied analytical methods to verify the determined optical properties. [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]

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]