Degradation Of Cell Performance Research Articles

Multi-scale coupled mechanical-electrochemical modeling for study on stress generation and its impact on multi-layered electrodes in lithium-ion batteries

This study develops a physics-based mechanical-electrochemical coupled modeling framework to investigate the stress generation and its impact on cell performance. This framework is based on a multi-scale approach, from particle to cell level, and includes several layers of electrodes in lithium-ion batteries (LIBs). In LIBs, (de)intercalation-induced stress plays a significant role in battery performance and degradation; however, the key challenge is that its impact occurs across multiple scales. The model integrates particle-level volume expansion into cell-level deformation, stress, and electrochemical performances. The study reveals that the volume changes due to lithium intercalation generate significant stress, which can easily break the binder and in-between particles. Compared with the substantial stress generated from active particles, the external pressure is much smaller and has an insignificant influence on the cell performance. However, these external pressures decrease the total thickness of the multi-layered electrodes and their variation. Inhomogeneous current inputs were also applied between the electrode layers, which showed a considerable degradation of cell performance. The developed model captures the effects of external pressure, the number of electrode layers, and inhomogeneous current inputs on the electrochemical-mechanical behaviors, which are critical for battery design and management from the particle level to larger-scale battery structures.

Theoretical Study of Charge Carrier Lifetime and Recombination on the Performance of Eco-Friendly Perovskite Solar Cell

Tin-based perovskite solar cell (PSC) has witnessed a focus in recent years. In this article, an inverted p-i-n planar hetero-junction structure for FASnI3 PSC is realized using device simulation software. We have studied the effect of relative permittivity ( $\varepsilon _{\text {r}}$ ), carrier lifetime ( $\tau$ ), and thickness on the performance of PSC. The fill factor (FF) is strongly dependent on carrier lifetime. In a uniformly doped device, maximum efficiency is obtained for high $\tau $ (>50 ns). Furthermore, the transport of charge carrier to the electrode is connected to the electric field. For low $\varepsilon _{\text {r}}$ , the electric field strength is high thus recombination of light generated carriers is low. The impact of different recombination effects on cell performance is also discussed. It is found that Shockley–Read–Hall (SRH) recombination is a major reason for the performance degradation of perovskite cells. The result shows that with optimized absorber properties, power conversion efficiency (PCE) 17.33% can be achieved. This study will aid researchers for better understanding of carrier dynamics process thus achieving high device efficiency in lead-free PSCs.

Effects of Beam Conditions in Ground Irradiation Tests on Degradation of Photovoltaic Characteristics of Space Solar Cells

We investigated the effects of irradiation beam conditions on the performance degradation of silicon and triple-junction solar cells for use in space. The fluence rates of electron and proton beams were varied. Degradation did not depend on the fluence rate of protons for both cells. A higher fluence rate of electrons caused greater degradation of the Si cell, but the dependence was due to the temperature increase during irradiation. Two beam-area expansion methods, defocusing and scanning, were examined for proton irradiation of various energies (50 keV–10 MeV). In comparing the output degradation from irradiation with defocused and scanned proton beams, no significant difference in degradation was found for any proton energy. We plan to reflect these findings into ISO standard of irradiation test method of space solar cells.

Predicting Platinum Dissolution and Performance Degradation under Drive Cycle Operation of Polymer Electrolyte Fuel Cells

A protocol is presented that allows for fuel cell performance degradation to be determined based on a vehicle drive cycle. Four stages are outlined beginning with the conversion of vehicle velocity data to a cell voltage profile. The amount of platinum dissolved in the system and oxide coverage on platinum particles are simultaneously calculated by considering several degradation mechanisms including Ostwald ripening and platinum particles loss to the membrane. The platinum loss is used to determine the Electrochemically Active Surface Area (ECSA) loss in the catalyst layer. The voltage loss due to platinum degradation is then determined from the ECSA data. The results show that longer times at higher upper potential limits lead to more platinum degradation and thus performance loss as expected. Accelerated Stress Test data is reproduced within the acceptable error. The model is applied to real-world data from a vehicle drive cycle showing that the model simplifications and assumptions outlined are reasonable and prove predictive capabilities. Although more experimental data would be beneficial to fully validate the model, the present work provides a complete, physics-based catalyst degradation model that can be integrated with performance models to predict durability and optimize future system designs and operating conditions. This paper is part of the JES Focus Issue on Proton Exchange Membrane Fuel Cell and Proton Exchange Membrane Water Electrolyzer Durability.

Plasma-Enhanced Atomic Layer Deposition of Zirconium Oxide Thin Films and Its Application to Solid Oxide Fuel Cells

Zirconium oxides were deposited using plasma-enhanced atomic layer deposition (PEALD) involving (2-(N-methylamino)1-MethylEthyleneCyclopentadienyl)Bis(DiMethylAmino)Zr (abbreviated as CMEN-Zr) and oxygen plasma as zirconium and oxygen sources. The zirconium oxide thin films demonstrate temperature-independent growth rates per cycle of 0.94 A/cycle at 150–215 °C. The deposited ZrO2 thin films were characterized using numerous analytical tools, i.e., X-ray photoelectron spectroscopy for chemical bonding state and composition, X-ray diffraction for crystallinity, atomic force microscopy for surface morphology, field-emission scanning electron microscopy for cross-sectional analysis, spectroscopic ellipsometry and UV–visible spectrophotometry for optical characterization, capacitance–voltage measurements for dielectric constants and atomic defects, and current–voltage characteristics for electrical information. The insulating features of the crystalline and stoichiometric ZrO2 films were implemented in the anode composites to evaluate the influence of ALD-based nano-features on the electrochemical performance of solid oxide fuel cells, with the main emphasis on anode performance. The presence of nanomaterials on Ni/YSZ anode composites is analyzed to determine the negative effects on electrochemical performance and the degradation of cell performance of solid oxide fuel cells (SOFCs). The artificial design was proven to be effective in controlling the cell performance as long as proper material design was adopted in SOFC electrodes.

Proton irradiation induced GaAs solar cell performance degradation simulations using a physics-based model

In this study a recently developed physics-based model to describe the performance degradation of GaAs solar cells upon electron irradiation is applied to analyze the effects of proton irradiation. For this purpose GaAs solar cells with significantly different architectures are subjected to a range of proton irradiation fluences up to 5×1012 H+/cm2. The resulting J−V and EQE characteristics of the cells are measured and compared with the simulations from the model. The model requires individual degradation constants for the SRH lifetimes and the surface recombination velocities as an input. In this study these constants were obtained from the recently determined associated constants for electron irradiation using the particles non-ionizing energy loss (NIEL) values for conversion. The good fit between the simulated and experimentally obtained results demonstrate that this is a valid approach. Moreover, it suggests that the physics based model allows for a good prediction of GaAs cell performance under particle irradiation of any kind independent of the particular cell architecture as long as the layer thicknesses and doping levels are known. In addition the applied proton irradiation levels in this study were not found to induce additional Cu-related degradation in the investigated thin-film cells, indicating that the use of copper foil as a convenient carrier and rear contact does not require reconsideration for thin-film cells intended for space applications.

Study on performance degradation and damage modes of thin-film photovoltaic cell subjected to particle impact

It has been a key issue for photovoltaic (PV) cells to survive under mechanical impacts by tiny dust. In this paper, the performance degradation and the damage behavior of PV cells subjected to massive dust impact are investigated using laser-shock driven particle impact experiments and mechanical modeling. The results show that the light-electricity conversion efficiency of the PV cells decreases with increasing the impact velocity and the particles’ number density. It drops from 26.7 to 3.9% with increasing the impact velocity from 40 to 185 m/s and the particles’ number densities from 35 to 150/mm2, showing a reduction up to 85.7% when being compared with the intact ones with the light-electricity conversion efficiency of 27.2%. A damage-induced conversion efficiency degradation (DCED) model is developed and validated by experiments, providing an effective method in predicting the performance degradation of PV cells under various dust impact conditions. Moreover, three damage modes, including damaged conducting grid lines, fractured PV cell surfaces, and the bending effects after impact are observed, and the corresponding strength of each mode is quantified by different mechanical theories.

Energy management optimal strategy of FCHEV based on the Radau Pseudospectral method

Energy management of the fuel cell hybrid electric vehicles (FCHEVs) is vital with respect to improving FCHEV's performance and durability. Radau Pseudospectral method (RPM)-based optimal control of energy management of FCHEV is proposed to optimise the fuel cell's lifetime by means of reducing its performance degradation. To utilise the RPM, both state and control variables are approximated by global interpolation polynomials, and differential equations of state variables are approximated by the derivatives of interpolation polynomials. Accordingly, the optimal control problem is transformed into nonlinear problem to be solved. The fuel cell's performance degradation is selected as objective function. The optimal results in NEDC show that battery with larger capacity is more beneficial than smaller one for reducing the fuel cell's performance degradation, with the total time of large load change of the fuel cell reducing. The RPM is also an effective way to optimise other objectives to energy management.

Energy management optimal strategy of FCHEV based on the Radau Pseudospectral method

Energy management of the fuel cell hybrid electric vehicles (FCHEVs) is vital with respect to improving FCHEV's performance and durability. Radau Pseudospectral method (RPM)-based optimal control of energy management of FCHEV is proposed to optimise the fuel cell's lifetime by means of reducing its performance degradation. To utilise the RPM, both state and control variables are approximated by global interpolation polynomials, and differential equations of state variables are approximated by the derivatives of interpolation polynomials. Accordingly, the optimal control problem is transformed into nonlinear problem to be solved. The fuel cell's performance degradation is selected as objective function. The optimal results in NEDC show that battery with larger capacity is more beneficial than smaller one for reducing the fuel cell's performance degradation, with the total time of large load change of the fuel cell reducing. The RPM is also an effective way to optimise other objectives to energy management.

Three-dimensional modeling of performance degradation of planar SOFC with phosphine exposure

A three-dimensional computational model is developed to predict the performance degradation of planar SOFC anodes exposed to fuel contaminants commonly present in coal syngas. The model parameters are calibrated using data from button cell experiments. The calibrated model is then used to perform simulations to predict performance degradation of planar cells due to phosphine contamination. The results from degradation simulations show that the contaminant coverage alters the current and temperature distributions significantly. The electrochemical characteristics of the degraded cell are analyzed by performing impedance and polarization simulations. The impedance analysis is applied to the cell in three regions along the fuel flow direction to elucidate location specific degradation phenomena. The results show that the degradation rates and the impedance behavior of planar cells are very different and more complicated than those observed in button cells. In such cases, localized impedance analysis may be necessary to elucidate various degradation mechanisms.

A prospective study of anti-vibration mechanism of microfluidic fuel cell via novel two-phase flow model

Microfluidic fuel cell is considered as a cleaner energy conversion device, and has potential commercial applications in portable electronic devices owing to its appreciable output power, prolonged work time and low emission. In a liquid-fed cell, however, a gaseous phase is generated, and the corresponding vibration effects have a considerable influence on performance. Thus, it is important to analyse the effects of the two-phase flow and vibration on the characteristics of a microfluidic fuel cell. A two-phase computational model is constructed for a microfluidic fuel cell employing a flow-over electrode. Multiple physical processes are coupled in the model, including the hydrokinetics, electrochemical reaction kinetics, species transport, vibration field, Euler-Euler model, and phase transfer. Results indicate that the aggravated vibration intensity and frequency lead to a negative effect comprising a critical fuel crossover and delayed gaseous discharge, resulting in the cell performance degradation. Besides, increasing the contact angle and flow rate contribute to a reduction in the gaseous volume fraction, but the latter considerably sacrifices fuel utilisation and exergy efficiency. The present work provides insights for the future development of anti-vibration elements and optimised cell design, and offers a reference for the sustainable practical application of microfluidic fuel cell.

Heterostructured Nickel-Rich LiNi0.91Co0.05Mn0.04O2 cathode Materials via Exfoliation-Restacking of Anionic Clay

Nickel-rich layered lithium transition-metal oxides, LiNi1−xMxO2 (M = transition metal, x < 2), have been under intense investigation as high-energy cathode materials for rechargeable lithium batteries because of their high specific capacity and relatively low cost. However, the commercialization of nickel-rich oxides has been severely hindered by their intrinsic poor thermal stability at the fully charged state and insufficient cycle life, especially at elevated temperatures. Here, the surface of a nickel-rich layered cathode particles was modified with anionic clay via an exfoliation and restacking route. The nickel-rich layered cathode particles and anionic clay are well-matched with each other regarding electrostatic interactions, allowing the two inorganics to spontaneously self-assemble when mixed with each other in aqueous media. The electron energy loss spectroscopy profile demonstrated a very thin coating layer around 2.5 nm beyond the Ni boundary originating from the cathode particles. The resulting material displayed suppressed gas evolutions as well as thermal and electrochemical properties, which both theoretical and experimental results showed were due to homogenous passivation via a thin coating layer. The cylindrical-type 18650 cell was tested for longer cycles and at an elevated temperature (45 °C) in order to accelerate the side reactions between the active cathode materials and the electrolyte. The prepared cathode material had discharge capacities of 233 mAh/g at 0.2 C and 82.4 % capacity retention after 300 cycles, which showed much improved retention compared to non-surface modified particles (71.0 %). In addition, amount of transition metal dissolution that occurred after cycling, which is strongly related to degradation of cell performances when using Ni-rich cathode materials. Reducing of metal dissolution was successfully achieved by modifying the surface on the cathode material particles and dissolution of Ni ions was dramatically reduced by a factor of 8 compared to non-surface modified particles. Figure 1

Angstrom-Thick Oxide Overcoat on Decorated Nanoclusters for Enhanced Performance and Durability of SOFC Cathodes

A solid oxide fuel cell (SOFC) is an energy conversion system with high conversion efficiency, high power density and fuel flexibility.1 Since its durability and cost issues are largely originated from the high temperature operation, intense efforts have been made to reduce the operational temperature to an intermediate range of 600 – 800 °C.2 The decrease in temperature, however, results in a significant decrease in the electrochemical kinetics in particular of the oxygen reduction reaction (ORR) occurring at the cathode.3,4 Atomic layer deposition (ALD) is an emerging low-temperature chemical vapor deposition variant that can deposit well-dispersed islands or uniform films at the atomic scale even on a highly corrugated geometry.8,9 By leveraging the capability, researchers have successfully improved SOFC durability mainly by suppressing the agglomeration of high-surface-area electrodes10–13 and/or dopant segregation to the surface of perovskite-based cathodes.14,15 Considering the capability of ALD to perform a conformal atomic-scale treatment on complex geometry, an ALD treatment can be best leveraged when applied to a structure of extreme surface area as opposed to conventional porous backbone structures. However, its application to a high-surface-area electrodes (e.g. infiltrated electrodes) and associated analysis is rarely reported.In this presentation, we demonstrate that a uniform atomic-scale oxide overcoat (either ceria or yttria with a nominal thickness of 0.7 – 1.5 Å) by ALD is highly effective not only in the enhancement of thermal stability of underlying ceria nanoparticles (5 – 20 nm) infiltrated on LaNi0.6Fe0.4O3- d (LNF) backbone (~100 nm) but also in the facilitation of oxygen reduction kinetics. Since LNF does not suffer from Sr segregation, a major degradation mechanism,17 the analysis of cell performance degradation is simplified. Based upon electrochemical and physical characterization of a series of infiltrated and/or ALD-treated samples, we discuss the impact of surface treatment on the nanoscale morphology, surface chemistry and electrode performance.We provide a quantitative analysis of the thermal agglomeration of NPs with and without ALD treatment and prove the close correlation between the NP agglomeration and electrode performance degradation. To the best of our knowledge, this is the first work showing the correlation in a quantitative manner. In addition, we demonstrate that an angstrom-scale ALD overcoat dramatically enhances the electrode performance in terms of polarization resistance and its activation energy for both bare LNF and ceria-infiltrated LNF electrodes. The improved electrode activity from ALD treatment is mainly ascribed to a significant facilitation of O2 dissociative adsorption with a partial reduction, with the aid of surface-specific oxygen-deficient and catalytically active ceria.The authors acknowledge the support from the Korea Institute of Industrial Technology (KITECH) and U.S. National Science Foundation CAREER Award (DMR 1753383). The use of TEM at the Molecular Foundry was supported by the U.S. Department of Energy (Contract No. DE-AC02-05CH11231). The XPS work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory (Contract DE-AC52-07NA27344). Sossina M. A high-performance cathode for the next generation of solid-oxide fuel cells, 431, 170, 2004Kang H., Grewal S., Li H., Lee M. H. Effect of Surface-Specific Treatment by Infiltration into LaNi6Fe4O3-δ Cathodic Backbone for Solid Oxide Fuel Cells, 166, 255, 2019

Acetonitrile Contamination and Recovery of Pemfcs

The proton exchange membrane fuel cell (PEMFC) is still considered a promising power source for transportation and stationary applications. Electrochemical catalysts and the proton exchange membrane (PEM) are the two key components that determine cell performance. The catalyst promotes fuel cell reactions generating electricity for the external load whereas the PEM completes the circuit by transporting protons. Air pollution is detrimental to both PEMFC performance and durability (1). Acetonitrile, is a critical pollutant that primarily originates from automobile exhausts and manufacturing facilities, where acetonitrile has been used as a solvent for spinning fibers and as an electrolyte in lithium batteries. The acetonitrile concentration in atmospheric air reaches values of up to 3 ppm in some areas (2). During PEMFC operation, acetonitrile is introduced into the cathode compartment by slippage through the air filter. The effects of acetonitrile on a PEMFC were investigated by in-situ operation and ex-situ electrochemical techniques (3,4). The results of in-situ tests showed that a trace amount of acetonitrile close to the atmospheric concentration caused significant short- and long-term damage, especially for MEAs with commercially relevant low Pt catalyst loadings (5,6). The ex-situ analysis indicated that acetonitrile not only impacted the oxygen reduction reaction by adsorbing on the Pt/C catalyst surface, but also affected the proton conductivity of ionomers and PEMs by ion exchange with its conversion products. Acetonitrile reaction products exhausted from an operating PEMFC were also identified by in-situ GC-MS and ex-situ water analysis (7). The acetonitrile reaction intermediates and products assisted the derivation of a contamination mechanism. Acetonitrile is hydrolyzed and reduced to NH3 and CH3CHO, and CH3COOH. Subsequent NH3 hydrolysis forming NH4 + gradually impacted the proton conductivity of the ionomer and PEM by accumulation. The other hydrocarbon products adsorbed on the surface of Pt catalysts competed with the main fuel cell reactions and were successively oxidized to harmless CO2.Automotive PEMFCs are exposed to variable operating conditions: startup, duty cycling, and shutdown. In this contribution, the effects of operating conditions on PEMFC contamination by acetonitrile are investigated. Contamination mechanisms are employed to analyze in detail cell performance degradation during contaminant injection and recovery after the contaminant injection was interrupted. Both steps involve at least two different processes. The adsorption and desorption of acetonitrile and/or its redox products dominate the fast cell voltage change occurring during the initial portion of both degradation and recovery steps. The ion exchange dominated the slower evolution in cell voltage during the latter part of both degradation and recovery steps. During cell contamination, the amount of water carried by reactant streams showed a considerable impact on performance degradation. The longer time needed to reach a steady state (see Figure 1) was attributed to ammonium scavenging by liquid water drops (8) delaying its accumulation. For the cell performance recovery step, the Pt catalyst activity and cathode potential only impact the earliest and shortest portion of the transient. As a result, the recovery duration is dominated by the ionomer and membrane ion exchange process, and is therefore less sensitive to contamination extent or operational history as previously observed (Figure 8 in (9)). Faster recovery strategies will be proposed based on the contamination mechanism and this detailed analysis of the operating condition effects.ACKNOWLEDGMENTSThis work was supported by the Department of Energy (DE-EE0000467) and the Office of Naval Research (N00014-19-1-2159). Authors are also grateful to the Hawaiian Electric Company for their ongoing support of the Hawaii Sustainable Energy Research Facility operations.REFERENCES J. St-Pierre, in Polymer Electrolyte Fuel Cell Durability, F. N. Büchi, M. Inaba, and T. J. Schmidt, Editors, p. 289, Springer (2009).http://www.epa.gov/airquality/airdata/index.html. Information accessed in August 2014.J. Ge, J. St-Pierre, Y. Zhai, Electrochim. Acta, 134 (2014) 272–280.Y. Zhai, J. Ge, J. St-Pierre, Electrochem. Commun., 66 (2016) 49–52.J. St-Pierre, Y. Zhai, Molecules, 25 (2020) article 1060.Y. Zhai, J. Ge, J. Qi, J. St-Pierre, J. Electrochem. Soc., 165 (2018) F3191–F3199.Y. Zhai, J. St-Pierre, Acetonitrile contamination reactions in PEMFCs, in preparation for ChemElectroChem.J. St-Pierre, B. Wetton, Y. Zhai, J. Ge, J. Electrochem. Soc., 161 (2014) E3357–E3364.Y. Zhai, J. St-Pierre, Appl. Energy, 242 (2019) 239–247. Figure 1. Cell voltage transients during the PEMFC contamination by acetonitrile for different combinations of reactant stream relative humidities. Figure 1

Understanding the Mechanisms for Recoverable Vs. Unrecoverable Aemfc Degradation

In recent years, there has been significant improvement in the achievable current and peak power densities as well as the longevity of anion exchange membrane fuel cells (AEMFCs). However, cell performance degradation remains an area of concern for the technology and a key to reducing performance decline is understanding mechanisms at work – which includes both recoverable and irrecoverable (irreversible) losses. To date, very few studies have been done that aim to understand and counter performance degradation mechanisms, while those that have generally focused only on irrecoverable performance degradation (such as AEM and ionomer instability). The present study highlights the mechanisms for recoverable voltage loss in operating AEMFCs – mainly associated with water management and exposure to CO2. The purpose of this talk is to highlight both the fundamental principles underlying recoverable voltage loss as well as modern approaches to mitigate and control these mechanisms. Reducing the influence of water and CO2 on AEMFC behavior is very important for their performance, lifetime and operational stability, which will be shown by 2000+ hour durability experiments showing extremely low voltage decay rates.

Multiple cycle chromium poisoning and in-situ electrochemical cleaning of LSM-based solid oxide fuel cell cathodes

Electrochemical cleaning, a recently proposed mitigation strategy for chromium poisoning in solid oxide fuel cell (SOFC) cathodes, involves rapid in-situ removal of Cr 2 O 3 deposits from LSM-YSZ cathodes accompanied by a recovery of a large fraction of the cell performance originally lost due to Cr poisoning. By operating the cell briefly as a solid oxide electrolyzer cell (SOEC), the cleaning method effectively reverses the Cr deposition reactions, reforming Cr-containing vapor species, thereby freeing up electrochemically active sites and restoring cell performance. In practice, this method can be periodically applied to the system after a specified amount of degradation due to chromium poisoning has occurred. The current study investigates the efficacy of this method by cycling a single cell through a stage of accelerated poisoning followed by electrochemical cleaning for a total of three times. Current-voltage measurements demonstrate repeated loss in performance due to Cr poisoning and recovery in performance due to electrochemical cleaning, reinforcing the utility of this cleaning method over the lifetime of the cell operation. • Chromium poisoning leads to degradation in cell performance. • In-situ electrochemical cleaning can be achieved by running the cell under mild electrolytic conditions. • The electrochemical cleaning process removes Cr 2 O 3 deposits and restores cell performance. • The electrochemical cleaning process does not damage the cell microstructure. • The cleaning process can be used effectively multiple times without changing cell temperature.

Fuzzy Model Based Control for Energy Management and Optimization in Fuel Cell Vehicles

Energy management system is vital to fuel cell vehicles in fuel economy and system durability. In this paper, we investigate the problem of controlling energy flow in charge-sustaining fuel cell vehicles by considering system stability, optimality and fuel cell durability. The energy management problem is transformed to a nonlinear optimization problem with multi-objectives in order to improve fuel economy, maintain battery state of charge, and reduce the incidence of factors affecting the fuel cell performance degradation. A robust model-predictive-based fuzzy control method is employed to design the nonlinear control law. The energy management system is capable of coordinating with a fuel cell stack state of health estimator and an energy storage system scheduler to achieve the optimization objectives in the presence of uncertainty of the driver's power demand. The effectiveness of the new design technique developed is demonstrated by conducting studies on control performance over typical urban/highway driving scenarios.

Importance of Interfacial Passivation in the High Efficiency of Sb2Se3 Thin-Film Solar Cells: Numerical Evidence

In this paper, we demonstrate numerical evidence that interfacial passivation in the Sb2Se3 solar cell forming the configuration of indium tin oxide (ITO)/SnO2/CdS/Sb2Se3/Au is beneficial for suppressing defects and obtaining cells with high efficiency. First, the effects of two types of defects including bulk defects in the Sb2Se3 absorber layer and interfacial defects at the CdS/Sb2Se3 interface on the performance of solar cells are studied, respectively. It is found that the effect of the bulk defects varied greatly in different magnitudes of defect density, whereas significant deterioration could be caused by the interfacial defect at relatively lower defect density. Then, the types of three actual defects named D1, D2, and D3 measured experimentally in the Sb2Se3 solar cells are analyzed by comparing the simulation and experimental results. It is found that the case D1 and D2 existing in the absorber layer while D3 located at the interface makes the simulation and experimental results the most consistent, in which the interfacial defect D3 contributes the most to the degradation of cell performance. Finally, a SnO2-free Sb2Se3 solar cell sample is simulated to evaluate the crucial interfacial passivation effect of the SnO2 layer. The results show that introducing a SnO2 layer is beneficial for the passivation of not only the interfacial defects but some unclear mechanisms such as deep-level defects which are hard to be measured in the present experiment. The numerical simulation results provide evidence proving the importance of interfacial passivation in actual fabrication processes to improve the performance of Sb2Se3 solar cells.

Numerical simulation of an innovative high efficiency solar cell with CdTe/Si composite absorption layer

As the improvement in efficiency of CdTe solar cell becomes more and more difficult, it is very necessary to engage in research on CdTe solar cell with innovative structure or new materials. In this work, we first proposed a design idea of constructing cadmium telluride on silicon to form a CdTe/Si composite absorption layer and then achieving an innovative high efficiency solar cell with a basic structure of n-Zn1-xMgxO/p-CdTe/p-Si/Au. This kind of solar cell has the advantages of relatively high open-circuit voltage and large short-circuit current, because photons with a wavelength range of 825 nm–1100 nm can not be absorbed by CdTe with a bandgap of 1.5 eV while they can be absorbed by silicon with a bandgap of 1.12 eV, thereby extending the long-wave response of sunlight. Numerical simulation of solar cell was carried out by using SCAPS-1D software to study the impacts of materials parameters such as thickness, doping concentration, valence band offset (VBO) and interface state density of CdTe/Si on device performances. Results indicated that thinner CdTe and suitable thick Si were beneficial for the cell with high efficiency. Particularly, the interface states between CdTe and Si severely degraded cell performance, so an innovative CdSixTey layer was proposed for the first time to effectively reduce the lattice mismatch and modify the interface properties between CdTe and Si. Finally, the highest theoretical conversion efficiency of 28.36% accompanied by open-circuit voltage of 0.838 V, short-circuit current of 39.28 mA/cm2, and fill factor of 86.11% of solar cell with SnO2:F/Zn1-xMgxO/CdTe/CdSixTey/Si/ZnTe:Mo/Au structure was obtained by optimizing numerical simulation design.

Evidence for a Light‐Induced Degradation Mechanism at Elevated Temperatures in Commercial N‐Type Silicon Heterojunction Solar Cells

The response of commercial n‐type silicon heterojunction (SHJ) solar cells to illuminated annealing at temperatures between 75 and 180 °C is reported on. Although a slight increase in efficiency of 0.1% absolute occurs at 75 °C under 1 sun illumination after 20 h, annealing at higher temperatures (85–180 °C) results in significant degradation in cell performance, and only occurs in the presence of illumination. At 160 °C, a loss inηup to 1% absolute is observed under 1 sun light soaking (LS) in as little as 2 min. Further illuminated annealing leads to a subsequent partial or full recovery of cell performance. At 160 °C, after an initialVOCdegradation exceeding 10 mV within 3 min, a complete recovery is obtained after 60 min of illuminated annealing. The results indicate the potential presence of a light‐induced degradation mechanism in n‐type SHJ cells, suggesting care must be taken when using LS to improve efficiency. In addition, significant variability in the maximum extent of degradation indicates a high degree of cell‐to‐cell variation in expression of this degradation mechanism. The exact nature of the underlying defect mechanism(s) governing degradation and recovery dynamics remains uncertain and requires further studies.