Aluminum Doping Effects on Interface Depletion Width of Low Temperature Processed ZnO Electron Transport Layer-Based Perovskite Solar Cells

Rapid improvement in efficiency and stabilities of perovskite solar cells (PSCs) is an indication of its prime role for future energy demands. Various research has been carried out to improve efficiency including reducing the exciton recombination and enhancement of electron mobilities within cells by using electron transport material (ETM). In the present research, electrical, optical, and depletion width reduction properties of low temperature processed ZnO electron transport layer-based perovskite solar cells are studied. The ZnO thin films vary with the concentration of Al doping, and improvement of optical transmission percentage up to 80% for doped samples is confirmed by optical analysis. Reduction in electrical resistance for 1% Al concentration and maximum conductivity 11,697.41 (1/Ω-cm) among the prepared samples and carrier concentration 1.06×1022 cm−3 were corroborated by Hall effect measurements. Systematic impedance spectroscopy of perovskite devices with synthesized ETM is presented in the study, while the depletion width reduction is observed by Mott Schottky curves. IV measurements of the device and the interfacial charge transfer between the absorber layer of methylammonium lead iodide and ETM have also been elaborated on interface electronic characteristics.

Novel Negative Capacitance and Conductance in All Temperatures and Voltages of Au/CNTs/n-Si/Al at Low and High Frequencies

The structure of carbon nanotube CNTs functioning as p-type material deposited over n-type silicon to produce heterojunction of Au/CNTs/n-Si/Al is presented in this study.This work explored the capacitance and conductance at various frequencies, temperatures, and voltages, the novelty here is that negative capacitance and conductance were observed at high frequencies in all temperatures and voltages, whereas capacitance appeared at both high and low frequencies, such as (2x107,1x107,1x102,10) Hz. At high-frequency f = 2x107 Hz, the capacitance raises while the conductance decreases; at all temperatures and voltages, the capacitance and conductance exhibit the same behavior at particular frequencies such as 1x106,1x105,1x104,1x103Hz, however their behavior differs at 2x107,1x107, 1x102 and 10Hz. Investigating the reverse square capacitance with voltage yielded the energy fermi (Ef), density surface of states (Nss), depletion width (Wd), barrier height, series resistance, and donor concentration (Nd)

G-Doping-Based Metal-Semiconductor Junction

Geometry-induced doping (G-doping) has been realized in semiconductors nanograting layers. G-doping-based p-p(v) junction has been fabricated and demonstrated with extremely low forward voltage and reduced reverse current. The formation mechanism of p-p(v) junction has been proposed. To obtain G-doping, the surfaces of p-type and p+-type silicon substrates were patterned with nanograting indents of depth d = 30 nm. The Ti/Ag contacts were deposited on top of G-doped layers to form metal-semiconductor junctions. The two-probe method has been used to record the I–V characteristics and the four-probe method has been deployed to exclude the contribution of metal-semiconductor interface. The collected data show a considerably lower reverse current in p-type substrates with nanograting pattern. In the case of p+-type substrate, nanograting reduced the reverse current dramatically (by 1–2 orders of magnitude). However, the forward currents are not affected in both substrates. We explained these unusual I–V characteristics with G-doping theory and p-p(v) junction formation mechanism. The decrease of reverse current is explained by the drop of carrier generation rate which resulted from reduced density of quantum states within the G-doped region. Analysis of energy-band diagrams suggested that the magnitude of reverse current reduction depends on the relationship between G-doping depth and depletion width.

Comprehensive Analytical Modelling of an Absolute pH Sensor

In this work, we present a comprehensive analytical model and results for an absolute pH sensor. Our work aims to address critical scientific issues such as: (1) the impact of the oxide degradation (sensing interface deterioration) on the sensor’s performance and (2) how to achieve a measurement of the absolute ion activity. The methods described here are based on analytical equations which we have derived and implemented in MATLAB code to execute the numerical experiments. The main results of our work show that the depletion width of the sensors is strongly influenced by the pH and the variations of the same depletion width as a function of the pH is significantly smaller for hafnium dioxide in comparison to silicon dioxide. We propose a method to determine the absolute pH using a dual capacitance system, which can be mapped to unequivocally determine the acidity. We compare the impact of degradation in two materials: SiO2 and HfO2, and we illustrate the acidity determination with the functioning of a dual device with SiO2.

Impact of defect states on the capacitance voltage characteristics of space charge limited organic diodes, and determination of defect states

The capacitance rise in low frequency C–V curves originates due to diffusive storage of injected carriers within the bulk in the case of intrinsic devices, whereas a voltage dependent depletion width is the cause in the case of devices having traps.

Energy band alignment at the heterointerface between CdS and Ag-alloyed CZTS

Energy band alignment at the heterointerface between CdS and kesterite Cu2ZnSnS4 (CZTS) and its alloys plays a crucial role in determining the efficiency of the solar cells. Whereas Ag alloying of CZTS has been shown to reduce anti-site defects in the bulk and thus rise the efficiency, the electronic properties at the interface with the CdS buffer layer have not been extensively investigated. In this work, we present a detailed study on the band alignment between n-CdS and p-CZTS upon Ag alloying by depth-profiling ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). Our findings indicate that core-level peaks and the valence band edge of CdS exhibit a significant shift to a lower energy (larger than 0.4 eV) upon the etching of the CdS layer, which can be assigned due to band bending and chemical shift induced by a change in the chemical composition across the interface. Using a simplified model based on charge depletion layer conservation, a significantly larger total charge region depletion width was determined in Ag-alloyed CZTS as compared to its undoped counterpart. Our findings reveal a cliff-like band alignment at both CdS/CZTS and CdS/Ag-CZTS heterointerfaces. However, the conduction-band offset decreases by more than 0.1 eV upon Ag alloying of CZTS. The approach demonstrated here enables nanometer-scale depth profiling of the electronic structure of the p–n junction and can be universally applied to study entirely new platforms of oxide/chalcogenide heterostructures for next-generation optoelectronic devices.

Measurement of Junction Depth in Sub-Micron Device Using SIMS Technique for Performance Estimation in RF Range

This chapter shows the measurement procedure of junction depth using SIMS method with detailed experimental procedure, and the result is verified by theoretical computation. SIMS profile is analytically characterized by Pearson's distribution function, and all the results together established the fact that the device can be utilized for operating as a diode in RF range; where ion dose is considered as a variable parameter with ion energy. Implanted impurity distribution profile is obtained as a function of depletion width from which junction depth can be evaluated. Straggle parameters and projected range profile near the ion energy range is computed for which depth is evaluated, and skewness & kurtosis are estimated to get a theoretical knowledge of all the moments assuming the Pearson IV distribution. Results suggest that distribution of atoms may be considered as Gaussian in nature.

Improving the interfacial properties of CZTS photocathodes by Ag substitution

Ag substitution improves the photocurrent and onset potential of CZTS/CdS/Pt photocathode to 17 mA cm−2 and 0.85 VRHE due to reduction of bulk and interface defects as well as increased depletion width.

Morphology, chemical and electrical properties of CdO Nanoparticles on porous silicon

In this paper, CdO nanoparticles prepared by pulsed laser deposition techniqueonto a porous silicon (PS) surface prepared by electrochemical etching of p-type silicon wafer with resistivity (1.5-4Ω.cm) in hydrofluoric (HF) acid of 20% concentration. Current density (15 mA/cm2) and etching times (20min). The films were characterized by the measurement of AFM, FTIR spectroscopy and electrical properties. Atomic Force microscopy confirms the nanometric size.Chemical components during the electrochemical etching show on surface of PSchanges take place in the spectrum of CdO deposited PS when compared to as-anodized PS. The electrical properties of prepared PS; namely current density-voltage characteristics under dark, show that the pass current through the PS layer is more than that obtained from the CdO/PS/Si which is related to increasing junction resistivity that come from increasing in depletion width.