Optical and electrical properties of thin films

Performance Analysis of Calcium-Doped Titania (TiO2) as an Effective Electron Transport Layer (ETL) for Perovskite Solar Cells

Ca-doped TiO2 films were synthesized by the modified sol-gel method and employed as the electron transport material of perovskite solar cells (PSCs). Morphological, optoelectronic, thermal, and electrical studies of thin films were investigated through XRD, RAMAN, SEM, AFM, UV-Vis, FTIR, and IV characteristics. Ca doping was detected with the help of structural properties while morphological analysis revealed that thin films based on Ca-doped titania are crack-free, homogenous, and uniformly distributed. Further optoelectronic properties have shown a promising conversion efficiency of 9.79% for 2% Ca-doped titania followed by 1% Ca-doped titania, while 3% have shown the lowest conversion efficiency among these prepared samples. The 2% an optimized doping of Ca has shown an almost two-fold increase in conversion efficiency in comparison to pristine TiO2, along with an increase in current density from 15 mA⋅cm−2 to 19.3 mA⋅cm−2. Improved energy efficiency and higher current density are attributed to faster electron transportation; moreover, the optimized percentage of Ca doping seems to be an effective approach to improve the PSCs’ performance.

Random matrix approach to plasmon resonances in the random impedance network model of disordered nanocomposites

Random impedance networks are widely used as a model to describe plasmon resonances in disordered metal-dielectric and other two-component nanocomposites. In the present work, the spectral properties of resonances in random networks are studied within the framework of the random matrix theory. We have shown that the appropriate ensemble of random matrices for the considered problem is the Jacobi ensemble (the MANOVA ensemble). The obtained analytical expressions for the density of states in such resonant networks show a good agreement with the results of numerical simulations in a wide range of metal filling fractions 0<p<1. A correspondence with the effective medium approximation is observed.

Dielectric and diamagnetic susceptibilities near percolative superconductor-insulator transitions

Coarse-grained superconductor-insulator composites exhibit a superconductor-insulator transition governed by classical percolation, which should be describable by networks of inductors and capacitors. We study several classes of random inductor-capacitor networks on square lattices. We present a unifying framework for defining electric and magnetic response functions, and we extend the Frank-Lobb bond-propagation algorithm to compute these quantities by network reduction. We confirm that the superfluid stiffness scales approximately as [Formula: see text] as the superconducting bond fraction p approaches the percolation threshold p _c . We find that the diamagnetic susceptibility scales as [Formula: see text] below percolation, and as [Formula: see text] above percolation. For models lacking self-capacitances, the electric susceptibility scales as [Formula: see text]. Including a self-capacitance on each node changes the critical behavior to approximately [Formula: see text].

Divergence of dynamical conductivity at certain percolative superconductor-insulator transitions

Random inductor–capacitor (LC) networks can exhibit percolative superconductor-insulator transitions (SITs). We use a simple and efficient algorithm to compute the dynamicalconductivity σ(ω,p) of one type of LC network on large (4000 × 4000) square lattices, where δ = p − p(c) is the tuning parameter for the SIT. We confirm that the conductivity obeys a scaling form, so that the characteristic frequency scales as∝|δ|(νz) with νz ≈ 1.91, the superfluid stiffness scales as ϒ∝|δ|(t) with t ≈ 1.3, and the electric susceptibility scales as χE∝|δ|(−s) with s = 2νz − t ≈ 2.52. In the insulating state, the low-frequency dissipative conductivity is exponentially small, whereas in the superconductor, it is linear in frequency.The sign of Im σ(ω) at small ω changes across the SIT. Most importantly, we find that right at the SIT Re σ(ω) ∝ ω(t/νz−1)∝ω(−0.32), so that the conductivity diverges in the DC limit, in contrast with most other classical and quantum models of SITs.

Interplay between structural randomness, composite disorder, and electrical response: resonances and transient delays in complex impedance networks

We study the interplay between structural and conductivity (composite) disorder and the collective electrical response in random network models. Translating the problem of time-dependent electrical response (resonance and transient relaxation) in binary random composite networks to the framework of generalized eigenvalues, we study and analyze the scaling behavior of the density of resonances in these structures. We found that by controlling the density of shortcuts (topological randomness) and/or the composite ratio of the binary links (conductivity disorder), one can effectively shape resonance landscapes or suppress or enhance long transient delays in the corresponding random impedance networks.

Aqueous latex/ceramic nanoparticle dispersions: colloidal stability and coating properties

The effect of pH on the colloidal stability of aqueous dispersions containing antimony-doped tin oxide (ATO) or indium tin oxide (ITO) nanoparticles and poly(vinyl acetate-acrylic) copolymer (PVAc-co-acrylic) latex particles was investigated using experimental observations and Derjiaguin, Landau, Verwey and Overbeek (DLVO) theory. The microstructure, electrical properties and optical properties of composite coatings prepared from various dispersions were also studied. Zeta potential measurements revealed that the isoelectric point (IEP) of ATO nanoparticles was below pH 2.0, that of ITO nanoparticles was at pH approximately 6.0 and that of PVAc-co-acrylic latex was at pH approximately 2.0. ATO/PVAc-co-acrylic dispersions prepared at pH 3 were stable, but those prepared at pH 1.5 formed aggregates, which settled quickly with time. DLVO theory predictions are in accord with these results. Stable ITO/PVAc-co-acrylic dispersions are obtained at a pH of 3.0 and 11.0, but dispersions are not stable at a pH of 6.0, the IEP of ITO. At a pH of 3.0, DLVO results predict attraction between ITO particles and latex particles. Dispersion pH affected the microstructures and properties of ATO (or ITO)/PVAc-co-acrylic coatings. Suspensions that formed aggregates produced coatings with lower percolation thresholds and lower transparencies than those produced from stable suspensions.