Admittance Spectroscopy Research Articles

Defect characterization by differential capacitance spectroscopy without the Arrhenius plot

A new method of Arrhenius transformation and matching is developed in this study based on the rate-temperature duality of the admittance spectroscopy measurement to extract the activation energy Ea and the attempt-to-escape frequency ν0 of a defect in GaAsN from differential capacitance spectroscopy without the Arrhenius plot and without identifying the fdC/df spectra peaks. The method consists of a set of variations that transform the iso-rate scan and/or the isothermal scan to a virtual space-activation energy, attempt-to-escape frequency, temperature, or rate. The transformed scans must be matched prior to extracting Ea and ν0 local to a fixed point in the two-dimensional temperature-rate experimental space.

Dielectric Properties of Au/SrTiO3/p-Si Structure Obtained by RF Magnetron Sputtering in a Wide Frequency Range

Dielectric properties of Au/p–Si structure with Strontium titanate (SrTiO3) interlayer were examined in the frequency range of 100–900 kHz (by step 100 kHz). SrTiO3 thin film was deposited on p-type Si substrate using radio frequency (RF) magnetron sputtering method at a substrate temperature of 500 °C. Dielectric parameters such as dielectric constant (e′), dielectric loss (e′′), real modulus (M′), imaginary modulus (M′′), and electrical conductivity (σac) of the Au/SrTiO3/p-Si structure were calculated by evaluating the results obtained from admittance spectroscopy in the frequency range of 100–900 kHz by step 100 kHz. According to the obtained results, e′ values take negative values as a result of depending on frequency measurements.

Investigation of Defect‐Tolerant Perovskite Solar Cells with Long‐Term Stability via Controlling the Self‐Doping Effect

AbstractAlthough there have been significant advances in the stability of perovskite solar cells through encapsulation techniques to remove extrinsic degradation factors, such as moisture and oxygen, irreversible photo‐degradation originating from intrinsic defects is still challenging and remains elusive. Herein, the photo‐aging mechanism due to intrinsic defects is investigated in nitrogen‐filled conditions, excluding extrinsic degradation factors. Devices with similar power conversion efficiencies (PCE) of 21%, but with different Fermi levels in the perovskite films, via controlling the self‐doping effect, have been investigated. Opto‐electronic investigations and depth profiles of the elemental constituents show that after photo‐aging, strain relaxation in the perovskite lattice and a Fermi level shift towards conduction band edge are observed, implying the formation of new defect states in Pb‐rich devices. Furthermore, thermal admittance spectroscopy measurement of the devices suggests that the formation of the deep‐traps in the perovskite leads to irreversible degradation. Thin‐film solar cells that are relatively Pb‐deficient (FA‐rich) exhibit improved long‐term stability, retaining over 90% of their initial PCE during 500 h of continuous 1‐Sun illumination. This study suggests passivation of the Pb‐I related antisite defects near the grain boundaries and the interface is crucial for the fabrication of solar cells with enhanced long‐term stability.

Effect of combined treatment of cesium fluoride as precursor and post-treatment on Cu(In,Ga)Se2 thin film solar cell

In this study, we investigate the combined effect of cesium fluoride (CsF) as a precursor and post-treatment on a Cu(Inx,Ga1-x)Se2 (CIGS) thin film solar cell fabricated onto sodalime glass substrates. The combined treatment improves the open-circuit voltage, fill factor, and cell efficiency of the solar cell compared with its single counter treatment. Secondary ion mass spectroscopy measurements show a higher concentration of Cs diffusion in the surface regions in the combined treatment, which change the electronic properties of the buffer/CIGS interface by reducing interfacial recombination. Solar cells fabricated using CsF as a precursor indicate a deterioration in device performance owing to the formation of bulk defects, as confirmed from admittance spectroscopy. This study unveils device performance improvement by combining a heavy alkali metal as a precursor and post-treatment on CIGS thin film solar cells.

Influence of the Reaction Pathway on the Defect Formation in a Cu2ZnSnSe4 Thin Film.

Point defect engineering in Cu2ZnSnSe4 (CZTSe) thin films is the main issue to improve its device performance. This study reveals the correlation between the reaction pathway and the point defects in the CZTSe film. The reaction pathway from a metallic precursor (Mo/Zn/Sn/Cu) to a kesterite CZTSe film is varied by changing the annealing process. The synthesized CZTSe films under different reaction pathways induce different device performances with different defect energy levels, although all CZTSe films have similar structural and optical properties (Eg ∼ 1.0 eV). The admittance spectroscopy demonstrates the correlations between point defect types (VZn, ZnSn, ZnCu, CuZn, and VCu) and the reaction pathways for the formation of CZTSe films. The different growth rates of binary selenides, such as ZnSe and/or Sn-Se phases, during the annealing process are especially strongly related to the formation of point defects, leading to the different open-circuit voltages (396-451 mV) and fill factors (51-65%). The results of this study suggest that controlling the reaction pathway is an effective approach to adjust the formation of defects in the kesterite CZTSe film as well as to fabricate high-performance solar cell devices.

On the relation between mobile ion kinetics, device design, and doping in double-cation perovskite solar cells

Contribution of mobile ions to current transport in double cation FA1−xCsxPbI3 p–i–n solar cell structures with NiOx hole transport layers and electron transport layers (ETLs) formed by Phenyl-C61-butyric acid methyl ester (PCBM) or C60 was studied by means of our previously developed suite of techniques comprising admittance spectroscopy, Deep Levels Transient Spectroscopy with standard (DLTS) and reversed (RDLTS) sequence of biasing/pulsing, and Photoinduced Open-Circuit Voltage Voc Spectroscopy (PIVTS). These studies show that the amplitudes of mirror-like peaks in DLTS/RDLTS, the hallmark of mobile ions, strongly decrease when switching from PCBM to C60 and further decrease with the addition of Cl to the growth solution. A similar effect is observed in PIVTS spectra monitoring changes in long-time open circuit Voc relaxations with temperature. The activation energies of peaks in DLTS, PIVTS, and low-frequency admittance spectra are similar to each other. The results indicate that switching the ETL type from PCBM to C60 and adding Cl in the perovskite ink for improved crystallization result in alleviating adverse effects of mobile ions, which correlates with observed changes in solar cell performance and reliability. Possible reasons for the described phenomena will be discussed.

Defect Characterization Using Raw Admittance Spectroscopy

We report a characterization technique that offers substantial improvement over the conventional practice of admittance spectroscopy, specifically in the processing of the admittance signal and the...

Admittance spectroscopy of dopants implanted in silicon and impurity state-induced AC magnetoresistance effect

A silicon structure doped with Ga using ion implantation has been investigated by admittance spectroscopy. It has been established that the presence of the Ga impurity, along with the B one, in the silicon structure leads to the appearance of the second peak in the temperature dependence of the real part of the impedance (admittance). Moreover, switching-on a magnetic field parallel to the sample plane shifts the singularities in the temperature curve to the high-temperature region. This results in the manifestation of both the positive and negative magnetoresistance effect upon temperature and magnetic field variation. It has been found by the standard admittance spectroscopy analysis of the impedance data that the energy structure of the investigated sample includes two interfacial energy levels ES1(0) = 42 meV and ES2(0) = 69.4 meV. As expected, these energies are consistent with the energies of B and Ga dopants. In a magnetic field, these levels increase by 3 meV for B and 2 meV for Ga, which induces the magnetoresistance effect. It has been demonstrated that the interfacial state-induced magnetoresistance effect can be tuned by ion implantation and dopant selection.

Admittance spectroscopy and material modeling for organic electronic applications

Abstract Organic materials, both insulators and semiconductors, led to impressive applications in recent years and particular attention was paid to their performance reliability under realistic atmospheric conditions, fundamental need for the feasibility of organic electronic devices. In this context one of the most critical topics is the investigation of elements affecting device performance, such as trap states at the interface between different materials, and a fundamental target is to provide reliable physical models. By the means of admittance spectroscopy, in this paper, an electrical model was developed to explain the different dynamics of an organic device. Every element of the model was connected to each other through different relationships, each describing a single process. The model provides an efficient parameter extraction method, allowing for example the characterization of the diffusion of mobile ions, the dispersive transport in organic semiconductor bulk, the contact resistance at the metal-organic interface. As a consequence, the model is useful to compare the properties and the performance of devices with respect to the geometries, the materials and the fabrication process conditions.

DETECTION OF FALSIFICATION OF HORILKA BY ADMITTANCE SPECTROSCOPY

The methods of quality control of horilka by electrical parameters, in particular, dielectric constant, specific conductivity, and imitation components are analyzed. The research results of individual samples of alcohol solutions and horilkas of different brands by the method of admittance spectroscopy were also analyzed. Based on this, methods for detecting falsification of horilka products by the method of admittance spectroscopy are proposed. The reactive component of the control object's ad is selected as an informative parameter. Two types of falsification are analyzed. The first is the falsification of the original horilka by replacing it with an aqueous-alcohol solution. The second - by replacing one brand of horilka with another. The analysis of the obtained results of researches of two types of objects on reactive components of their admittance in the frequency range 100 Hz100 kHz showed the following: characteristic features of dependencies of reactive components on frequency are revealed; they have been found to have extreme values at different frequencies. The reactive component of the admittance of aqueous-alcohol solutions reaches an extreme value at the beginning of the range. The same component of the original horilkas of different brands has extreme values at the end of the range. Based on this, methods for prompt detection of falsifications are proposed.

Исследование свойств солнечных элементов на основе селективного контакта MoO-=SUB=-x-=/SUB=-/Si с помощью спектроскопии полной проводимости

The possibility of using admittance spectroscopy to characterization the quality of ITO/MoOx/n-Si structures is shown. It has been demonstrated that magnetron sputtering of ITO layer at room temperature leads to radiation defects formation in the near-surface region of Si near the MoOx/Si interface with a depth of 0.13 and 0.26 eV below the conduction band with a capture cross-sectional area of (1–5)∙10^-19 and (5–10)∙10^-19 cm^-2, respectively. An increase in the deposition temperature of the ITO layer to 130 °C allows to reduce the concentration below the sensitivity leading to a significant improvement of solar cells characteristic.

Understanding deposition temperature dependent photovoltaic characteristics of Cu(In,Ga)Se2 solar cells: A study with thermally stable alkali aluminosilicate glass substrates

During 3-stage thermal co-evaporation of Cu(In,Ga)Se2 (CIGSe), alkali aluminosilicate (AAS) glass has proven to be stable at process temperatures Tmax of up to 650 °C. This is considerably higher than the maximum endurable Tmax for soda-lime glass (SLG), which is in the range of 530–550 °C. As the Na-content of the AAS glass used here is comparable to that of SLG, growing CIGSe at elevated Tmax is expected to promote Na diffusion from the glass substrate through the Mo back contact (BC) into the absorber layer. An increased Na concentration in the CIGSe absorber would be expected to result in an improved device performance as it is mostly associated with an increased open-circuit voltage (Voc) and fill factor (FF). This paper discusses the influence of varying Tmax from 530 to 650 °C during the 2nd and the 3rd stage of the 3-stage process on the morphological, electrical, and photovoltaic performance of CIGSe solar cells. Upon raising Tmax from 530 to 650 °C, the short-circuit current density (Jsc) decreased due to bandgap (Eg) widening. Glow discharge optical emission spectrometry analysis reveals that the Na concentration in the absorber is gradually decreased when elevating Tmax. As will be seen, we attribute this in part to a densification of the Mo BC during the high temperature process. A maximum conversion efficiency (η) was realized at Tmax = 600 °C. An increased Voc at Tmax = 600 °C is due to the wider Eg and to an increased carrier concentration despite the fact that the Na concentration in the CIGSe thin film was low compared to lower Tmax. Admittance spectroscopy analysis is performed to access information on defect energy level and density in the finished devices. In the light of present findings, ways to further improve η at elevated Tmax are suggested.

Capacitance characterization of silicon nanowires formed by cryogenic dry etching

Arrays of silicon nanowires were fabricated by dry etching in the ICP mode in a mixture of SF6/O2 gases at a temperature of-140 °C. Defects located near the wafer surface with E a =0.30 eV, σ=(1–10)×10−14 cm2 and E a =0.68–0.74 eV, σ=1×10−15 cm2 were detected by admittance spectroscopy and deep-level transient spectroscopy. An increase in the dry etching time from 3.5 min (for the 1st sample) to 4.5 min (for the 2nd sample) leads to an rise of their concentration, but additional stage of wet etching in 4% KOH during 30 s leads to a vanish of the response from the first sample (N T ˂1011 cm−3), while for the second sample the defect concentration becomes in two times lower.

Identification of LiNi and VNi acceptor levels in doped nickel oxide

Nickel oxide, in particular in its doped, semiconducting form, is an important component of several optoelectronic devices. Doped NiO is commonly achieved either by incorporation of lithium, which readily occupies Ni sites substitutionally, producing the LiNi acceptor, or by supplying reactive oxygen species during NiO film deposition, which leads to the formation of Ni vacancies (VNi). However, the energetic position of these acceptors in the NiO bandgap has not been experimentally determined until today. In this work, we close this knowledge gap by studying rectifying n++p heterojunctions consisting of NiO thin films grown on top of fluorine-doped tin oxide. These structures show sufficient rectification to perform electric characterization by defect spectroscopic techniques, specifically capacitance–voltage and thermal admittance spectroscopy. Using these methods, the (0/−) charge transition levels are determined to be 190 meV and 409 meV above the valence band edge for the LiNi and the VNi acceptor, respectively.

Defect spectroscopy and non-ionizing energy loss analysis of proton and electron irradiated p-type GaAs solar cells

Admittance spectroscopy combined with non-ionizing energy loss (NIEL) analysis is shown to be a powerful tool for analyzing solar cell radiation degradation, not relying on the change of macroscopic cell parameters. GaAs component cells, representative of the middle sub-cell in Ga0.5In0.5P/GaAs/Ge solar cells, were irradiated with protons and electrons in the 0.5–3 MeV energy range. Four irradiation-induced defects are identified in the p-type base layer. The nature of each defect is assessed by analyzing the dependence of its introduction rate on the NIEL deposited by electrons in the semiconductor. The expected linear relationship is only achieved if a unique threshold energy Ed is ascribed to each defect, which ranges from 9 to 38 eV. An electron NIEL with Ed=21eV, customarily used for GaAs-based solar cell degradation analysis, is an approximation of the relative abundance of these four defects. The 21 eV value is thus a GaAs material-specific parameter, independent of the electrical device design. In addition, the type and energy of the incident particle is correlated with the relative abundance of high Ed defects. The impact of each defect on the macroscopic electrical parameters of the cell, namely, the open-circuit voltage VOC, the short-circuit current density JSC, and the recombination current density J02, is assessed with the help of a Pearson analysis. The different effectiveness of electron and proton irradiation on parameters dominated by recombination in the depleted region, such as VOC or J02, is attributed in part to the influence of the particle recoil spectra on the defect capture cross section.

Charge carrier performance of phosphazene-based ionic liquids doped hole transport layer in organic light-emitting diodes

The enhancement of hole injection layers is strongly important issue for obtaining high-efficient and low-driving-voltage Organic Light-Emitting Devices (OLEDs). In this paper, we presented a comprehensive electroluminescence (EL) study of phosphazene-based ionic liquids (PzILs) used as a hole transport layer in solution-processed OLEDs. Charge transfer properties of PzILs were investigated by doping in poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS) at different ratios (0.1, 0.2, 0.5, 1.0, 2.0). Previously synthesized four types of PzILs (namely PzIL1, PzIL2, PzIL3, and PzIL4) were prepared in de-ionized water with 10 mg/ml concentration, mixed with PEDOT:PSS and examined for their charge transport characteristics on OLED device performance due to their ionic nature. The device with PzIL1 exhibited the best performance with luminance 4185 cd/m2 compared to other devices with and without PzILs. Further, Density Functional Theory (DFT) calculations and admittance spectroscopic analysis of OLEDs based on four types of PzILs were studied profoundly. Admittance spectroscopy has been used for revealing the carrier transport properties, mobility and the equivalent circuit modeling of the devices. Four types of PzILs OLEDs represented typical p-type transporting characteristics with moderate mobility up to 1.93 cm2/V.s.

Photon-induced defects and dynamics of photogenerated carriers in Cu(In,Ga)Se2 thin film solar cells

A detailed understanding of charge-carrier behavior could provide new avenues to improve the performance of the solar cell by enhancing the active materials and electronic properties. In the present work, the transport mechanism of photogenerated carriers in Cu(In,Ga)Se2 or CIGS)-based solar cells is investigated by analysis of the temperature-dependent current density-voltage (J-V) curves obtained under various illumination (i.e., dark, AM 1.5G, 650 nm, and 405 nm). The results demonstrate that J-V curve distortion, termed the “roll-over” effect, is significantly correlated with the illumination wavelength and, more importantly, is strongly associated with the persistent characteristics of the CIGS solar cell. In addition, the nature of the photo-induced defects and their influence on the transport mechanism of the photogenerated carriers were investigated via deep level capacitance profiling (DLCP) and admittance spectroscopy (AS) under various illumination conditions. The photo-capacitance results indicate distinct spatial distributions and persistent behaviors depending upon the illumination wavelength. Based on the findings in this work, the origin of the non-ideal J-V behavior in the CIGS solar cell is explained, and the spatial defect distribution and illumination wavelength sensitivity are discussed.

Influence of growth temperature on defect states throughout the bandgap of MOCVD-grown β -Ga2O3

The influence of growth temperature on the distribution (concentrations and energy levels) of individual defect states in metal organic chemical vapor deposition-grown, Si-doped β-Ga2O3 is investigated. A combination of deep level thermal transient/optical spectroscopies and admittance spectroscopy (AS) was used to quantitatively monitor the evolution of trap states throughout the ∼4.8 eV bandgap. States are observed at EC-0.12 eV by AS; at EC-0.4 eV by deep level transient spectroscopy; and at EC-1.2 eV, EC-2.0 eV, and EC-4.4 eV by deep level optical spectroscopy, and showed different dependencies on growth temperatures ranging from 800 °C to 920 °C. The EC-0.4 eV and EC-4.4 eV states both displayed a strong reduction in its concentration with increasing growth temperature, whereas no consistent trends were seen for the states at EC-1.2 eV and 2.0 eV over the temperature range studied. In contrast, the concentration of the EC-0.12 eV trap monotonically increased over the same range of increasing growth temperature, which tracked a slight, monotonic increase in overall Si concentration measured by secondary ion mass spectroscopy with growth temperature. The opposing trends in concentrations for some of these states shifted the dominant deep level in the bandgap from the EC-4.4 eV state at the lowest growth temperature explored here to the EC-0.12 eV state at the highest growth temperature. The shifting dominance of various bandgap states can have important ramifications on β-Ga2O3 device behavior, and the different trends for these deep levels cannot only guide further growth optimization but also advance the identification of their physical sources.

Effects of post-deposition CdCl2 annealing on electronic properties of CdTe solar cells

The effects of post-deposition CdCl2 annealing temperature on the electronic properties of CdTe solar cells were investigated. CdTe devices incorporate Mg doped ZnO as a buffer layer and selenization using a CdSe interlayer for reducing the buffer/absorber interface recombination and increasing solar energy absorption respectively. The post-deposition CdCl2 annealing treatments were done under separate, inert atmospheres of nitrogen and helium across the temperature range 380–430 °C. Electrical characterization of devices is carried out including temperature dependent current-voltage characteristics, admittance spectroscopy, and Shockley-Read-Hall recombination analysis. The best improvements in device efficiency are obtained upon annealing at temperature 410 °C. This anneal correlated with reduced back contact barrier in CdTe and reduced grain-boundary barrier height which is beneficial for enhanced charge transport.

Structural, electrical properties and complex impedance analysis of Pr0.67Ba0.22Sr0.11Mn1−xTixO3 perovskites

The Pr0.67Ba0.22Sr0.11Mn1−xTixO3 (x = 0.05 and 0.075) manganites are synthesized using solid-state reaction route. All XRD patterns with narrow and intense diffraction peaks reveal that the samples are well crystallized. For electrical properties we measure the conductivity versus temperature (80–400 K) and frequencies (40 Hz–10 MHz). These measurements were made by admittance spectroscopy technique. The effect of titanium doping on the electrical properties of our compounds appears by semiconductor behavior. The variation of DC-conductivity with temperature presents two metal–semiconductor transitions. The first transition TMS bound by Mn3+/Mn4+ ratio but the second transition TSM depends to an extrinsic effect of grain boundaries. It was observed also that the conductivity decreases with titanium concentration, such behavior is associated to a reduction of double-exchange mechanism. The conduction mechanism is explained by thermally activated hopping of small polaron at high temperature range. The activation energy was evaluated of about Ea = 30 m eV for x = 0.05 and Ea = 61 meV for x = 0.075. The total conductance spectrum of Pr0.67Ba0.22Sr0.11Mn0.925Ti0.075O3 compound is well described by the Jonscher power law: $$G\left(w\right)={G}_{dc }+A{\omega }^{n}$$ . Impedance study for the sample with x = 0.075 indicates the presence tow metal–semiconductor transitions and a non-Debye relaxation phenomenon related to a grain and grain boundary medium. Also, the modulation of the material by an electrical equivalent circuit show high values of grain boundary medium capacity.