Generation Lifetime Research Articles

Dynamics of Nonlinear Optical Losses in Silicon‐Rich Nitride Nano‐Waveguides

AbstractFree carrier absorption (FCA) is established to be the cause of nonlinear losses in plasma‐enhanced chemical vapor deposition (PECVD) silicon‐rich nitride (SRN) waveguides. To validate this hypothesis, a photo‐induced current is measured in SRN thin films with refractive indices varying between 2.5 and 3.15 when a C‐band laser light is illuminating the SRN films at various powers, indicating the generation of free carriers. Furthermore, nonlinear loss dynamics is, for the first time, measured and characterized in detail in SRN waveguides by utilizing high peak power C‐band complex shape optical pulses for estimation of free carrier generation (FCG) and free carrier recombination (FCR) lifetimes and their dynamics. Both FCG and FCR are found to decrease with an increase in the refractive index of SRN, and, specifically, the FCR lifetimes are found (92 ± 7) ns, (39 ± 3) ns, and (31 ± 2) ns for the SRN indices of 2.7, 3, and 3.15, respectively. Lastly, nonlinear losses in high refractive index SRN waveguides are demonstrated to be minimized and altogether avoided when the pulse duration reduced below the free carrier generation lifetime, thus providing a way of taking a full advantage of the large inherent SRN nonlinear properties.

Molecular Control of the Donor/Acceptor Interface Suppresses Charge Recombination Enabling High-Efficiency Single-Component Organic Solar Cells.

Single-component organic solar cells based on double cable polymers have achieved remarkable performance, with DCPY2 reaching a high efficiency of over 13%. In this study, DCPY2 is further optimized with an efficiency of 13.85%, maintaining a high fill factor (FF) without compromising the short circuit current. Despite its intermixed morphology, DCPY2 shows a reduced recombination rate compared to their binary counterpart (PBDB-T:Y-O6). This slower recombination in DCPY2 is attributed to the reduced wavefunction overlap of delocalized charges, achieved by spatially separating the donor and acceptor units with an alkyl linker, thereby restricting the recombination pathways. Adding 1,8-diiodooctane (DIO) into DCPY2 further reduced the recombination rate by facilitating acceptor aggregation, allowing free charges to become more delocalized. The DIO-assisted aggregation in DCPY2 (5% DIO) is evidenced by an increased pseudo-pure domain size of Y-O6. Fine molecular control at the donor/acceptor interface in the double-cable polymer achieves reduced non-geminate recombination under efficient charge generation, increased mobility, and charge carrier lifetime, thereby achieving superior performance. Nevertheless, the FF is still limited by relatively low mobility compared to the blend, suggesting the potential for further mobility improvement through enhanced higher-dimensional packing of the double-cable material.

Fluorine-free approaches to impart photovoltaic systems with self-cleaning and anti-icing features

Dust deposition on photovoltaic systems has a significant impact on the transmittance, temperature, and roughness, causing reductions in their power generation efficiency and lifetime. A promising approach to deal with this problem relies on the use of superhydrophobic coatings to impart the surfaces of these devices with self-cleaning properties. In this work, materials with different chemistry and morphology were added to an acrylic dispersion to create hydrophobic surfaces using a non-fluorinated coating simple strategy for glass substrates. Results showed that materials with more complex morphology, namely the spherical shape of silica nanoparticles, and the needle-like and prism-like structures of zinc oxide, imparted the glass with higher water contact angles. All coatings prepared displayed self-cleaning features and good adhesion to the glass substrate. Coatings comprising silica nanoparticles, zirconia and alumina modified with HDMTS were the best ones to prevent ice formation. In terms of chemical stability, all the coatings resisted acidic conditions close to acid rain pH and solvents with mild polarity. Therefore, the coatings proposed hold great potential to expel dust contaminants and prevent ice formation of photovoltaic devices, increasing their lifetime and power generation efficiency.

Tunable Optical Properties and the Role of Defects on the Carrier Lifetimes of Cs3Sb2I9 Synthesized in Various Solvents

Pb‐free halide perovskites have recently attracted immense attention due to the number of advantages in their optical and electronic properties. However, tuning the optical bandgap with minimized amounts of point defects is a particularly challenging task in photovoltaics. It is pivotal to clearly understand the detailed relationship between the bandgap change with defect generation and charge carrier lifetime. In this study, Cs3Sb2I9 crystals are synthesized by varied choice of solvents, namely, γ‐butyrolactone, a mixture of dimethylformamide and dimethyl sulfoxide, and hydroiodic acid. Although the same principles of decreasing solubility and crystallization are applied, Cs3Sb2I9 crystals with different size and shape in microscopic and macroscopic scale are obtained during heating and cooling of the solution. The synthesized crystals are investigated using a combination of different spectroscopies including Raman, UV–visible, and time‐resolved photoluminescence. In the results, it is suggested that there is a strong relationship between Urbach energy and the lifetime of charge carriers. In this research, readily applicable practical principles and examples of how to control the defects for the advancement in Pb‐free perovskite photovoltaics are provided.

Trifolium repens L.-Like Periodic Micronano Structured Superhydrophobic Surface with Ultralow Ice Adhesion for Efficient Anti-Icing/Deicing.

Wind turbine blades are often covered with ice and snow, which inevitably reduces their power generation efficiency and lifetime. Recently, a superhydrophobic surface has attracted widespread attention due to its potential values in anti-icing/deicing. However, the superhydrophobic surface can easily transition from Cassie-Baxter to Wenzel at low temperature, limiting its wide applications. Herein, inspired by the excellent water resistance and cold tolerance of Trifolium repens L. endowed by its micronano structure and low surface energy, a fresh structure was prepared by combining femtosecond laser processing technology and a boiling water treatment method. The prepared icephobic surface aluminum alloy (ISAl) mainly consists of a periodic microcrater array, nonuniform microclusters, and irregular nanosheets. This three-scale structure greatly promotes the stability of the Cassie-Baxter state. The critical Laplace pressure of ISAl is up to 1437 Pa, and the apparent water contact angle (CA) is higher than 150° at 0 °C. Those two factors contribute to its excellent anti-icing and deicing performances. The results show that the static icing delay time reaches 2577 s, and the ice adhesion strength is only 1.60 kPa. Furthermore, the anti-icing and deicing abilities of the proposed ISAl were examined under the environment of low temperature and high relative humidity to demonstrate its effectiveness. The dynamic anti-icing time of ISAl in extreme environments is up to 5 h, and ice can quickly fall with a speed of 34 r/min when it is in a horizontal rotational motion. Finally, ISAl has excellent reusability and mechanical durability, with the ice adhesion strength still being less than 6 kPa and the CA greater than 150° after 15 cycles of icing-deicing tests. The proposed structure would offer a promising strategy for the efficient anti-icing and deicing of wind turbine blades.

Charge Carrier Dynamics in Non-Fullerene Acceptor-Based Organic Solar Cells: Investigating the Influence of Processing Additives Using Transient Absorption Spectroscopy.

In this study, we present a comprehensive investigation into the charge generation mechanism in bulk-heterojunction organic solar cells employing non-fullerene acceptors (NFAs) both with and without the presence of processing additives. While photovoltaic devices based on Y6 or BTP-eC9 have shown remarkable power conversion efficiencies, the underlying charge generation mechanism in polymer:NFA blends remains poorly understood. To shed light on this, we employ transient absorption (TA) spectroscopy to elucidate the charge transfer pathway within a blend of the donor polymer PM6 and NFAs. Interestingly, the charge carrier lifetimes of neat Y6 and BTP-eC9 are comparable, both reaching up to 20 ns. However, the PM6:BTP-eC9 blend exhibits substantially higher charge carrier generation and a longer carrier lifetime compared to PM6:Y6 blend films, leading to superior performance. By comparing TA data obtained from PM6:Y6 or PM6:BTP-eC9 blend films with and without processing additives, we observe significantly enhanced charge carrier generation and prolonged charge carrier lifetimes in the presence of these additives. These findings underscore the potential of manipulating excited species as a promising avenue for further enhancing the performance of organic solar cells. Moreover, this understanding contributes to the advancement of NFA-based systems and the optimization of charge transfer processes in polymer:NFA blends.

Comparative Study of Transfer Functions for NRAD and AGN-201 Reactor Systems

The project is about building an infrastructure for an open loop technique and implementing this technique to measure the reactivity worth of small samples. The reactivity samples are allowed to oscillate back and forth in the reactor system to cause perturbations and the corresponding reactor response is measured in the form of the transfer function. The transfer function obtained is used to determine stability characteristics along with other kinetic parameters such as delayed neutron fraction, prompt neutron lifetime, shutdown margins, and absolute power. This paper compares transfer functions for reactors like Neutron Radiography (NRAD) and Aerojet General Nuclear (AGN-201). The magnitude of the transfer function correlates with the reactivity of the sample that caused the perturbation. In addition, the transfer function allows one to determine whether the reactor is a stable system or not. In other words, the reactor’s response to the change in neutron population in the reactor can be easily described. Moreover, a transfer function measurement is useful to extract important kinetic parameters of the reactor system, such as instance prompt neutron generation lifetime, reactivity shutdown margin, absolute power, etc. The transfer function plots presented in the results section correlate the reactivity of the sample that caused perturbations. NRAD was found to have a higher break frequency than that AGN-201. This was an expected result since break frequency is inversely proportional to neutron generation time. With this relation, break frequency was found to be around 306 Hertz. So, the reactor cannot respond beyond this frequency but passes the low frequencies. The corresponding analysis and comparative transfer function plots using MATLAB for these two reactor systems are presented in the results section. Many reactivity measurements have been already in practice however if the transfer function technique can give reactivity measurements with similar or better precision and accuracy, it could be a great benefit. Moreover, this can be installed in those facilities where more complex systems cannot be incorporated easily.

Label-Free Imaging Techniques to Evaluate Metabolic Changes Caused by Toxic Liver Injury in PCLS.

Abuse with hepatotoxic agents is a major cause of acute liver failure. The search for new criteria indicating the acute or chronic pathological processes is still a challenging issue that requires the selection of effective tools and research models. Multiphoton microscopy with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy (FLIM) are modern label-free methods of optical biomedical imaging for assessing the metabolic state of hepatocytes, therefore reflecting the functional state of the liver tissue. The aim of this work was to identify characteristic changes in the metabolic state of hepatocytes in precision-cut liver slices (PCLSs) under toxic damage by some of the most common toxins: ethanol, carbon tetrachloride (CCl4) and acetaminophen (APAP), commonly known as paracetamol. We have determined characteristic optical criteria for toxic liver damage, and these turn out to be specific for each toxic agent, reflecting the underlying pathological mechanisms of toxicity. The results obtained are consistent with standard methods of molecular and morphological analysis. Thus, our approach, based on optical biomedical imaging, is effective for intravital monitoring of the state of liver tissue in the case of toxic damage or even in cases of acute liver injury.

Electric Field-Enhanced Generation Current in Proton Irradiated InGaAs Photodiodes

Dark current degradation due to 49.7 MeV proton irradiation is studied on lattice-matched InGaAs PIN photodiodes. This degradation is described in terms of electric field enhanced Shockley-Read-Hall generation current in the depletion region. In this paper we present a model of the radiation-induced generation current which includes the role of the electric field through the generation rate field enhancement factor (GRFEF). Using a combination of dark current-voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">I_d – V</i> ) and capacitance-voltage ( <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">C – V</i> ) measurements, an experimental GRFEF is extracted for the thermal generation rate. This GRFEF has been used to define a new damage factor for InGaAs at low electric field that has been compared to previous literature studies. As a final result, the low-field generation lifetime degradation as a function of the fluence has been extracted.

Optical Biomedical Imaging Reveals Criteria for Violated Liver Regenerative Potential.

To reduce the risk of post-hepatectomy liver failure in patients with hepatic pathologies, it is necessary to develop an approach to express the intraoperative assessment of the liver's regenerative potential. Traditional clinical methods do not enable the prediction of the function of the liver remnant. Modern label-free bioimaging, using multiphoton microscopy in combination with second harmonic generation (SHG) and fluorescence lifetime imaging microscopy (FLIM), can both expand the possibilities for diagnosing liver pathologies and for assessing the regenerative potential of the liver. Using multiphoton and SHG microscopy, we assessed the structural state of liver tissue at different stages of induced steatosis and fibrosis before and after 70% partial hepatectomy in rats. Using FLIM, we also performed a detailed analysis of the metabolic state of the hepatocytes. We were able to determine criteria that can reveal a lack of regenerative potential in violated liver, such as the presence of zones with reduced NAD(P)H autofluorescence signals. Furthermore, for a liver with pathology, there was an absence of the jump in the fluorescence lifetime contributions of the bound form of NADH and NADPH the 3rd day after hepatectomy that is characteristic of normal liver regeneration. Such results are associated with decreased intensity of oxidative phosphorylation and of biosynthetic processes in pathological liver, which is the reason for the impaired liver recovery. This modern approach offers an effective tool that can be successfully translated into the clinic for express, intraoperative assessment of the regenerative potential of the pathological liver of a patient.

A Theoretical Investigation into pH of Neat Water at the Nanoscopic Scale Via Rexpon Force Field and Stochastic Simulations

Design of durable solar CO2 conversion devices requires a mechanistic understanding of molecular-level reactions at the electrode-electrolyte interface that lead to interfacial degradation.[1] This interface often incorporates such features as a porous and rough surface to maximize active area and enhance catalytic performance. However, this roughness may introduce local water pool inclusions, whose size may have an unforeseen, detrimental impact on device durability due to their local pH being very different from the bulk pH. It is well-recognized that for water pools containing less than molecules, the solution pH cannot be defined in the conventional sense because the pools are too small to support stable water ion concentrations near neutral pH. Rather, the water ion concentrations fluctuate to very high values for short periods of time. To better understand pH in small pools, we combine theoretical calculations using QM/MD and stochastic simulations [3]. We combined Ab initio MD and the accurate RexPoN force field [2] simulation to quantify the thermodynamic free energy to create water ion pairs through the reaction as a function of the water pool size. The free energies are used to calculate the equilibrium constants for this reaction and the ion pair generation and recombination rate constants. The rate constants are then used as inputs to the stochastic simulations to gain insights into ion pair generation frequency and lifetime statistics over extended periods of time (hours). Proton and hydroxide diffusion are also incorporated in the stochastic simulation to understand how far water ions may travel from where they are generated. The results show that the combination of Grotthuss and vehicular diffusion mechanisms for H3O+ and OH- can lead to unequal distributions at an adjacent interface. We will discuss how the stochastic generation and recombination of water ions influences buffer chemistry and dissolved CO2 chemistry.Reference[1] S. Nitopi, E. Bertheussen, S.B. Scott, X. Liu, A.K. Engstfeld, S. Horch, B. Seger, I.E.L. Stephens, K. Chan, C. Hahn, J.K. Nørskov, T.F. Jaramillo, I. Chorkendorff, Progress and Perspectives of Electrochemical CO2 Reduction on Copper in Aqueous Electrolyte, Chem. Rev. 119 (2019) 7610–7672. https://doi.org/10.1021/acs.chemrev.8b00705.[2] S. Naserifar, W.A. Goddard, The quantum mechanics-based polarizable force field for water simulations, J. Chem. Phys. 149 (2018). https://doi.org/10.1063/1.5042658.[3] W.D. Hinsberg, F.A. Houle, Kinetiscope, (n.d.). http://www.hinsberg.net/kinetiscope.

Lifetime Assessment of InxGa1−xAs n‐Type Hetero‐Epitaxial Layers

Herein, the carrier lifetime in ≈5 × 1016 cm−3 n‐doped InxGa1−xAs layers is studied by diode current–voltage analysis and by time‐resolved photoluminescence. Two sets of hetero‐epitaxial layers are grown on semi‐insulating InP or GaAs substrates. The first set corresponds with a constant In content p + n stack, while the second set has a fixedx = 0.53 for the n‐layer, while containing various extended defect densities by using a strain relaxed buffer with differentx. This results in threading dislocation densities (TDDs) between ≈105 cm−2and a few 109 cm−2. It is shown that the overall trend of the recombination lifetime versus TDD can be described by a first‐order model considering a finite recombination lifetime value inside a dislocation core of 1 nm. For the generation lifetime, a strong electric‐field enhancement factor is found. Also, the residual strain in the n‐layer has an impact. Overall, the safe limit for TDD depends on the type of application and on the operation conditions (reverse diode bias).

Comparison and Influence of Flywheels Energy Storage System Control Schemes in the Frequency Regulation of Isolated Power Systems

Increased renewable energy penetration in isolated power systems has a clear impact on the quality of system frequency. The flywheel energy storage system (FESS) is a mature technology with a fast frequency response, high power density, high round-trip efficiency, low maintenance, no depth of discharge effects, and resilience to withstand continuous charge-discharge cycling without lifetime degradation. These FESS properties allows to effectively address the frequency quality problem. This study analyzes the contribution of a FESS to reducing frequency deviations in an isolated system that combines a diesel plant, wind farm, and pump-storage hydropower plant based on the El Hierro power system. This study approaches this analysis by comparing six different FESS governor control schemes (GCSs). Of these six GCSs, the nonlinear proportional variant (NLP <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$_{\mathrm {V}}$ </tex-math></inline-formula> ) is a singular contribution based on the NLP scheme previously developed by the same researchers. Different governor’s parameter settings for the FESS GCSs were also compared, obtained from the proposed tuning methodology that considers the renewable energy generation distribution, frequency impact, and lifetime degradation of diesel, hydraulic groups, and flywheels. The GCSs were compared in terms of average frequency deviation, Zenith and Nadir frequency difference, wear and tear of diesel electromechanical elements and Pelton turbine nozzles, flywheels cycles per hour, and FESS average state of charge. The results show that including a FESS plant considerably improves frequency regulation. The tuning criteria and GCSs have a clear influence on the results, with NLP and NLP <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">V</sub> GCSs offering relevant improvements in frequency deviations.

Electrochemical study of a novel high-efficiency PbO2 anode based on a cerium-graphene oxide co-doping strategy: Electrodeposition mechanism, parameter optimization, and degradation pathways

A novel and efficient Ti/SnO2-Sb/PbO2-GO-Ce electrode was successfully fabricated based on the co-deposition of Ce ions and graphene oxide (GO) into β-PbO2 crystals and used as an anode for electrocatalytic oxidation of phenol. The electrodeposition mechanism, parameter optimization, mechanism analysis, and potential degradation pathways were discussed in depth. The co-doping of GO and Ce resulted in the high directional specificity of β(301), orderly and dense grain arrangement of PbO2 crystals. At the same time, the oxygen evolution potential, •OH generation capacity and lifetime were also improved. The effects of experimental parameters on phenol removal efficiency were evaluated, including the applied current density, electrode gap, supporting electrolyte, initial NaCl concentration, initial pH, and initial phenol concentration. Under the optimal conditions, the removal efficiency of phenol can reach 375.6 g m-2 h-1 for 20 min electrolysis, which is about 1.2 times that of the pure PbO2 electrode. The active oxygen species (•OH, ClO- and HClO) were important attributes to the degradation of phenol. Additionally, a potential degradation pathway for phenol was proposed. After 10 successive recycles, there was no significant difference of the electro-generated •OH, cell voltage and phenol removal rate, which confirms the stability and admirable reusability of Ti/SnO2-Sb/PbO2-GO-Ce electrode.

Modelling of environmental emission in Kenyan, Rwandan, and Tanzanian electrical power systems

There is limited information on environmental emissions in African grid electricity generation and transmission systems, especially from the sub-Saharan African countries. The developed parameters are useful for evaluating the extent to which grid electricity generation and transmission system drivers are designed and operated in the context of environmental governance (EG) factors. The environmental pressure caused by the studied power systems was evaluated in terms of carbon emission levels. To simplify the study, variable parameters were sampled from the national power grids of three sub-Saharan countries, namely: Kenya, Rwanda, and Tanzania. The developed inventory workbooks accounted for the residual carbon emissions related to the grid generation and transmission capacity survival lifetime, retired system capacity, and recycling rate, aiming to reduce the uncertainty in grid emissions in the study area. The obtained area of the curve for the business as usual and EG models reveals that Rwanda has the potential to contribute more emissions per unit power, followed by Tanzania and Kenya. The higher carbon emission uncertainty levels (65%–75%) obtained from the EG simuland and life cycle carbon emissions revealed that only limited EG factors were considered during the design and operation of the studied grid electricity generation and transmission systems. However, the possibility of significant lifetime decarbonisation performances from generation and transmission systems was also shown in the EG-modelled output, owing to its lower carbon emission uncertainty levels (15%–25%). The logarithmic regression trend lines presented by this research show a higher R2 value for the EG modelled life cycle carbon emission (LCCE) output (R2 = 0.8689) and EG simuland LCCE output (R2 = 0.9209), compared to EG modelled LCCE output (R2 = 0.7526) and EG simuland LCCE output (R2 = 0.8223) obtained from the linear regression trend lines, implying a very good relationship between the structural assumptions and simplifications constituting the model itself for case studied by the year 2049. The study suggests monitoring of a wide range of environmental parameters (apart from carbon) and associated energy storage technologies, considering both cumulative data and expanded systems.

(Invited) Defect Engineering for Monolithic Integration of III-V Semiconductors on Silicon Substrates

Implementation of high-mobility channel materials enables to increase the device performance due to the higher carrier mobility compared to silicon devices. III-V based materials such as GaAs and ternary systems (e.g. InxGa1-xAs alloys) are achieving high performing n-channel transistors. The strong progress in hetero-epitaxy using nano ridge engineering [1] leading to monolithic heterogeneous integration of III-V materials on silicon substrates resulted in state-of-the-art FinFETs, gate-all-around (GAA) and horizontal or vertical stacked nanowires (NW) on 300 mm Si wafers [2,3]. Very promising results have also been reported for GaN on Si triggering their use for high power and RF applications [4].One of the main challenges remains a good defect control in order not to degrade the electrical performance of devices and circuits [5]. The nucleation of extended defects is directly related to the hetero-epitaxial growth of layers with a lattice mismatch and their concentration depends on the composition of the layers such as e.g. the In content in InxGa1-xAs and the Al content in AlxGa1-xN. The defects have a direct impact on the generation and recombination lifetime and the leakage current [5], while also the low frequency noise (LFN) performance is influenced [6]. The identification of the defects (energy level ET, capture cross section and concentration) can be determined using Deep Level Transient Spectroscopy (DLTS) and low frequency noise spectroscopy by measuring LFN as a function of temperature.The goal of this work is to review the knowledge about defect engineering and to analyze the electrical activity of extended defects in III-V semiconductors on silicon substrates. Different case studies will be used to illustrate both the defect identification and the electrical activity of the defects. The impact of the used processing schemes to fabricate the devices is also discussed. It will e.g. be shown that defects in GaN/AlGaN MOSHEMTs increase the low frequency noise due to generation-recombination centers in the GaN depletion layer [7]. These traps can lead to a distortion of the current-voltage characteristics of short channel devices. DLTS studies are a powerful tool to identify traps and to investigate their impact on the leakage current of III-V on Si devices. Double correlation DLTS investigations on GaAs/InGaP/GaAs diodes pointed out that traps associated with sidewall interface states can dominate the peripheral diode leakage current. The focus of the presentation will be on the current understanding of defect engineering associated with the monolithic integration of III-V materials on Si and a discussion of recent results concerning the electrical activity of the defects and the defect modeling.[1] M. Baryshnikova et al., Crystals, 10, 330 (2020).[2] X. Sun et al., Digest VLSI Technology, T3-4 (2017).[3] A.P. Milemin et al., Microelectron. Eng., 192, 14 (2019).[4] L. Li et al., IEEE Electron Device Lett., 41, 689 (2020).[5] C. Claeys et al., ECS Solid State Electronics, 9, 03301 (2020).[6] C. Claeys et al., J. Phys. Cond. Ser., 1190, 012001 (2019).[7] K. Takakura et al., IEEE Trans. Electron Dev., 67, 3062 (2020).

Sub-Pico-Second Hole Generation Lifetime in Thin Film IGZO Sputtered and Annealed on P-Silicon Substrate

Indium-gallium-zinc-oxide (IGZO) sputtered and annealed in the absence of oxygen shows large oxygen vacancy concentration leading to n-type doping of the thin film. However, because of low intrinsic carrier concentration minority carrier (hole) concentration remains weak. Thus, measurement of thermal hole generation lifetime in unipolar IGZO is challenging. In this work, utilizing the charge transient of an appropriately biased depleted HfO2/IGZO thin film MOS capacitor fabricated on a p-silicon substrate, we extracted hole thermal generation lifetime of IGZO. The measured lifetime was found between 0.62–0.064 ps whence IGZO film received 400 °C to 700 °C anneal treatments followed by its direct sputtering on p-silicon substrate. Further, a morphology analysis of the IGZO was presented. Difference in the lifetime which occurred due to amorphous to the nano-crystalline transition of the IGZO thin film with increased anneal temperature was furthermore validated through XRD, SEM and AFM measurements. Hole capture cross-sections as we obtained from surface generation velocities at the IGZO/HfO2 interface and energy distributions of interface state density were found in agreement, which indirectly demonstrates the accuracy of the measured hole generation lifetime employing the transient capacitance extrapolation, since under the steady state condition hole generation through the interface states of IGZO/HfO2 tends to balance its bulk (IGZO) counterpart

Interplay between microstructure, defect states, and mobile charge generation in transition metal dichalcogenide heterojunctions.

Two-dimensional transition metal dichalcogenides (2D-TMDCs) have gained attention for their promise in next-generation energy-harvesting and quantum computing technologies, but realizing these technologies requires a greater understanding of TMDC properties that influence their photophysics. To this end, we discuss here the interplay between TMDC microstructure and defects with the charge generation yield, lifetime, and mobility. As a model system, we compare monolayer-only and monolayer-rich MoS2 grown by chemical vapor deposition, and we employ the TMDCs in Type-II charge-separating heterojunctions with semiconducting single-walled carbon nanotubes (s-SWCNTs). Our results suggest longer lifetimes and higher yields of mobile carriers in samples containing a small fraction of defect-rich multilayer islands on predominately monolayer MoS2. Compared to the monolayer-only heterojunctions, the carrier lifetimes increase from 0.73 μs to 4.71 μs, the hole transfer yield increases from 23% to 34%, and the electron transfer yield increases from 39% to 59%. We reach these conclusions using a unique combination of microwave photoconductivity (which probes only mobile carriers) along with transient absorption spectroscopy (which identifies spectral signatures unique to each material and type of photoexcited quasiparticle, but does not probe mobility). Our results highlight the substantial changes in photophysics that can occur from small changes in TMDC microstructure and defect density, where the presence of defects does not necessarily preclude improvements in charge generation.

Observing long-range non-fullerene backbone ordering in real-space to improve the charge transport properties of organic solar cells

The long-range backbone ordering in Y6 solid film is reported, which benefits charge generation and carrier lifetime in PM6:Y6 heterojunctions and drives the photovoltaic efficiency towards 16.8%.

Outdoor performance of organic photovoltaics at two different locations: A comparison of degradation and the effect of condensation

Tests on organic photovoltaics (OPV) mini modules, fabricated through a R2R process, in air and without hazardous solvents have been conducted in order to compare their outdoor performance, in Belo Horizonte, Brazil, and Bangor, North Wales, and assess the impact of the latitude and climate of the installation on the power generation and modules' lifetime. The test showed different profiles of degradation for each region and formulation, with a surprisingly faster degradation in Bangor. One of the possible sources of the increased degradation is the greater levels of condensation observed in Bangor. To verify the impact of condensation on the module stability, indoor tests have been conducted to relate the dew point depression to module degradation times. The results show that condensation is a significant stress factor in OPV and should be considered more prominently in reliability studies.