Drop In Open-circuit Voltage Research Articles

Engineering the active layer of lead-free perovskite (CH3NH3SnI3) solar cells using numerical simulation

We conduct a thorough numerical simulation to examine the impact of the thickness, defect density, and doping density of the active layer on the photovoltaic performance of the lead-free CH3NH3SnI3 perovskite solar cell (PSC). We observe that increasing the thickness of the active layer initially from 100 nm to 400 nm improved the power conversion efficiency (PCE) from 10.4% to 11.6%. However, further increasing the thickness to 800 nm resulted in a slight decline in PCE to 11.1%. This unexpected trend can be attributed to the high carrier mobility of charges in the CH3NH3SnI3 perovskite, which enables fast extraction of charge carriers, offsetting losses due to charge recombination. Increasing active layer trap density substantially declines the PCE from 11.5% at 1014 cm−3 to 7.5% at 1018 cm−3, as a result of the noticeable drop in open-circuit voltage (VOC) and fill factor (FF) with a growing defect density due to the enhancement in trap-assisted recombination. This is backed by a striking reduction in the shunt resistance upon increasing the defect density. Raising the active layer doping firstly enhances the PCE, reaching a peak value of 12.5% at the active layer doping density of 1017 cm−3, after which the PCE decreases as the doping density continues to increase. We explain these observations by energy level diagrams deduced at various doping levels.

Causes and mechanism of thermal runaway in lithium-ion batteries, contradictions in the generally accepted mechanism

In this paper, experimental results are analyzed that contradict the generally accepted scheme of thermal runaway reactions. Also, it was experimentally proved that three main exothermic reactions determine the thermal runaway process of lithium-ion batteries. The first main exothermic reaction of the thermal runaway is the reaction releasing the electrochemical energy accumulated in the lithium-ion batteries during their charging. The second main exothermic reaction of the thermal runaway is the reaction of lithiation of surface layers of a cathode active material; this reaction is performed by the lithium atoms coming from both the anode and the inner layers of the cathode active material. The third main exothermic reaction of the thermal runaway is the reaction of the cathode metal-oxides decomposition and the electrolyte oxidation by the released oxygen. Besides, it is shown here that the open circuit voltage drop in batteries during the thermal runaway is mainly due to the lithiation of the cathode active material and – to a much lesser extent – to short circuits occurrence of the electrodes. The established mechanism of thermal runaway of lithium-ion batteries makes it possible to quantitatively describe all currently known experimental results.

Radiation effects model for Ultra-Thin Silicon Solar Cells

This work is focused on investigation of radiation effects in Ultra-Thin Silicon solar cells with a particular emphasis on electron irradiation. The study is motivated by the application of these solar cells, developed by Solestial, Inc., for powering space missions, including those led by NASA, the Department Of Defence (DOD), and commercial satellite missions. Our research encompasses both experimental and theoretical approaches, addressing unique challenges posed by ultra-thin solar cell technology that deviates from the traditional models. From the experimental point of view, the test structures were irradiated with 1 MeV electrons up to the fluence of 1E+15 e/cm 2. Radiation effects due to accumulated electron dose were noticed as a drop in open-circuit voltage (Voc ). An analytical expression for modeling the Voc characteristic of the UT-Si cell after exposure to electron irradiation was formulated and subsequently compared with experimental data. The theoretical foundation of the proposed approach builds upon the Non-Ionising Energy Loss (NIEL) concept, a fundamental parameter in addressing radiation damage modelling and survivability predictions.

Life testing of 10 cm × 10 cm fuel-electrode-supported solid oxide cells in reversible operation

Reversible solid oxide cells (ReSOCs) can provide significant value by playing different roles – electrical generation or electricity storage – depending on the prevailing electrical grid requirements. Relatively few studies have focused on the life testing of solid oxide cells in this mode-switching operation, and much of that work has focused on small “button” cells. The present study describes electrochemical characterization and post-test characterization from an ∼2600 h life test of a 10 cm × 10 cm fuel-electrode-supported cell operated with periodically reversing current. The cell performance gradually decreased for the first ∼1000 h and then stabilized with low degradation rate until an abrupt test-ending gas crossover failure that resulted in open circuit voltage drop. Post-test characterization of the (La,Sr)CoO3-δ air-electrode showed evidence of Cr vapor contamination from stainless-steel manifolds and Ag contamination from current collection contacts. Partial delamination of the air-electrode and Gd-doped ceria interlayer was observed, along with fractures in the electrolyte near the fuel inlet that probably caused a drop in open circuit voltage near the end of the test. NiNi connectivity was reduced in both the functional and support layers accompanied by Ni particle coarsening, especially at the fuel outlet.

Addressing sodium ion-related degradation in SHJ cells by the application of nano-scale barrier layers

Silicon heterojunction (SHJ) solar cells are renowned for their high efficiency. However, SHJ solar cells are susceptible to various contaminants, leading to significant performance degradation when exposed to damp-heat conditions (e.g., 85 °C and 85% relative humidity). Sodium (Na) has been identified as one of the main contributors to degradation in silicon solar modules subjected to damp-heat conditions. This work investigates the role of an ultra-thin AlOx capping layer (∼10 nm) in preventing the failure in SHJ cells caused by Na-related contaminants. NaCl is applied directly to the solar cell, and the unencapsulated cell undergoes a damp heat test at 85 °C and 85% relative humidity (DH85). It is found that without the AlOx barrier layer, the SHJ cells experience a relative reduction in power of ∼30%rel after only 20 h at DH85. Both the front and rear sides of the cell degrade when exposed to NaCl. This is primarily due to a deterioration of the Ag contact resulting in increased series resistance (Rs), and decrease in fill factor (FF), and an increase in recombination, leading to a significant drop in open-circuit voltage (Voc), particularly when NaCl is applied on the rear side. However, when an AlOx barrier layer is applied to the SHJ cells, the performance losses caused by NaCl are significantly reduced to only ∼3.3%rel. The loss in Voc on the rear side is completely suppressed, and there is only a slight increase in Rs of ∼50%rel compared to ∼300%rel increase in Rs for cells without the AlOx barrier layer. These findings indicate that the ultra-thin AlOx barrier layer provides effective protection for SHJ cells against Na ions, mitigating both Rs and recombination losses. This AlOx barrier layer depositing method is compatible with existing industrial mass-production ALD tools and thus presents a viable solution at the cell level for SHJ cells.

The roles of acceptors in the thermal-degradation of P3HT based organic solar cells

The effects of acceptors on thermal degradation of thin film organic solar cells (OSCs) were investigated under the controlled environment. The popular donor polymer molecule, poly(3-hexylthiophene) (P3HT) is used in the preparation of bulk-heterojunction (BHJ) organic solar absorber medium. The evidences of degradation were observed from the changes of the optical and morphological properties of the polymer film. The parameters gathered from various characterization methods suggest that film degradation is indeed dependent on the nature of acceptor molecules used in the polymer matrix. Interestingly, the PC60BM acceptor blend solar absorber films are found to be more stable than ITIC based polymer blend. These are evident on the measured device parameters such as Jsc and Voc values that contribute to poor performance in P3HT:ITIC-based devices. It has been noted that a 50% drop in open-circuit voltage was recorded in ITIC based solar cell within an hour of thermal degradation. The FTIR result revealed that the production of -OH groups as a result of oxidation leads to the creation of trap states that hinder conductivity by decreasing short-circuit current.

A novel bilayer heterogeneous poly(ionic liquid) electrolyte for high-performance flexible supercapacitors with ultraslow self-discharge.

Flexible supercapacitors with high power density and long cyclic stability represent a promising candidate to be used as power supplies for portable electronics, but often suffer from the disadvantages of a limited working voltage and rapid self-discharge (spontaneous drop of open-circuit voltage). Here, we design a bilayer heterogeneous poly(ionic liquid) electrolyte (BHPE) consisting of a polycation complex and a polyanion complex with different zeta potentials to suppress the self-discharge of flexible symmetric supercapacitors. The resultant BHPE-based supercapacitors using active carbon/carbon nanotube composite electrodes exhibit a high working potential of 3.0 V and an energy density of 33 W h kg-1, which are comparable with those of devices obtained by using a homogeneous poly(ionic liquid) electrolyte (HPE). More significantly, the developed BHPE-based supercapacitor charged under forward bias exhibits a self-discharge time of 23.2 h, which is at least twice that of the device charged under reverse bias and is also much superior to those of HPE-based supercapacitors. The BHPE-based supercapacitors also possess excellent mechanical flexibility and stability, due to the stabilized interface contact between two layers of poly(ionic liquid)s.

Suppressed shuttle effect and Self-Discharge of redox electrochemical capacitors using biphasic electrolyte with a Liquid-Liquid interface

Redox-enhanced electrochemical capacitors (redox ECs) can boost the energy density of conventional ECs by introducing soluble redox species in the electrolyte to gain additional capacity via faradaic reactions. The shuttle effect of the added redox species such as polyiodides, however, leads to rapid self-discharge of redox ECs and severely limits their capability for long-term energy storage. Herein, we propose an ionic liquid (IL)-based aqueous biphasic system (ABS) as the electrolyte of iodide-based redox ECs to suppress the self-discharge. Based on molecular dynamics (MD) simulation and mechanistic analysis, we reveal that the liquid–liquid interface in the ABS blocks the diffusion of polyiodides and leads to reduced self-discharge rate. Specifically, EC cells with ABS electrolyte deliver much lower open circuit voltage (OCV) drop (0.7 V) and better energy retention (>32%) in 24 h than that of cells with conventional iodide-based electrolyte (OCV drop: 1.6 V, energy retention: 0%). This strategy is also successfully extended to the fabrication of ABS-based hydrogel electrolyte for solid-state redox ECs with low self-discharge rate. The results of this work not only provide a mechanistic approach to elucidating the effect of redox couples on the self-discharge of redox ECs, but also demonstrate an effective way of mitigating the shuttle effect via liquid–liquid interface in a biphasic electrolyte to reduce self-discharge.

Influence of QD array positioning in GaAs solar cell p-n junction on their photoelectric characteristics

In the work, the effect of In0.8Ga0.2As quantum dots position in the i-region of a GaAs solar cell on its spectral and photoelectric characteristics has been investigated. Three solar cell structures were obtained by metal-organic vapor-phase epitaxy, in which layers of quantum dots were placed in the middle of the i-region and also have been shifted to the base and the emitter. As a result, it has been shown that the solar cell with a quantum dot array shifted to the base demonstrates the smallest open-circuit voltage drop and, accordingly, a higher efficiency value.

Investigation of self-discharge properties and a new concept of open-circuit voltage drop rate in lithium-ion batteries

Investigation of self-discharge properties and a new concept of open-circuit voltage drop rate in lithium-ion batteries

Acetobacter Biofilm: Electronic Characterization and Reactive Transduction of Pressure.

The bacterial skin studied here is a several centimeter-wide colony of Acetobacter aceti living on a cellulose-based hydrogel. We demonstrate that the colony exhibits trains of spikes of extracellular electrical potential, with amplitudes of the spikes varying from 1 to 17 mV. The bacterial pad responds to mechanical stimulation with distinctive changes in its electrical activity. While studying the passive electrical properties of the bacterial pad, we found that the pad provides an open-circuit voltage drop (between 7 and 25 mV) and a small short-circuit current (1.5–4 nA). We also observed by pulsed tomography and spatially resolved impedance spectroscopy that the conduction occurs along preferential paths, with the peculiar side-effect of having a higher resistance between closer electrodes. We speculate that the Acetobacter biofilms could be utilized in the development of living skin for soft robots: such skin will act as an electrochemical battery and a reactive tactile sensor. It could even be used for wearable devices.

Performance Degradation of Lithium‐Ion Batteries with LiNi0.33Co0.33Mn0.33O2 Cathodes during Long‐Term, High‐Temperature Storage: Behaviors and Mechanism

AbstractThe behaviors and mechanism for the different performance degradation trends of 18650 cylindrical lithium‐ion batteries (LIBs) with LiNi0.33Co0.33Mn0.33O2 cathodes under long‐term storage at a high temperature (HT) of 80 °C are investigated to gain insight on the safe use of LIBs. It is indicated that the direct current resistance (DCR) increases sharply within 240 h and then slows down gradually, whereas the open‐circuit voltage (OCV) and the recoverable capacity (RC) fading are relatively stable in the initial 240 h, but then speeds up from 240 h to 720 h. With the aid of analyses of the anode, cathode, and separator materials in batteries stored at 80 °C for 0 h, 240 h, 480 h, and 720 h, the mechanism of the performance degradation of batteries is elucidated. It is pointed out that the DCR rise is mainly caused by the anode materials peeling off from the copper foil, as is the subsequent interface resistance increase. The RC fading is attributed to the partial break of the cathode structure, owing to the dissolution of transition metal ions (Ni2+, Co3+, and Mn4+), and the dissolution becomes more severe as the time extends. In addition, the separator suffers a combination of stretching (machine direction), squeezing (anode side), oxidation (cathode side), and destruction, resulting in internal short circuit and sharp OCV drop, as well as the other potential safety risks of LIBs. These results are valuable to establish an accelerated testing method to evaluate batteries in a short time range to advance the safe use of LIBs under high‐temperature storage.

Direct carbon fuel cell design for continuous operation

The design of a direct carbon fuel cell (DCFC) for continuous operation was successfully executed and is presented in this study. Petroleum coke, an abundant carbon source in Canada, was used as a fuel and pneumatically supplied to the anode side of the cell. The open circuit voltage (OCV) of the cell reached 1.1 V and generated a power density of 28 mW/cm2 at 700 °C and 85 mW/cm2 at 850 °C. After about 180 h of operation the cell's performance declined, due to loss of electrolyte. In the next design, a cell was fabricated with an electrolyte circulation loop. This cell generated a lower power density than the first cell assembly but its OCV drop during 180 h operation was significantly improved. These are the first molten carbonate DCFC results demonstrating continuous carbon supply and electrolyte recirculation with potential for ash and impurities removal.

The dependence of recombination in GaAs solar cells on the number of included GaInAs quantum objects

The experimental characteristics of GaAs p-i-n structures with InGaAs quantum objects (QOs) have been investigated. The study of electroluminescence spectra has shown that an increase of the number of QOs layers leads to relative increase in electroluminescence intensity from QOs and decrease it from the GaAs matrix. The observed increase in QOs recombination has resulted in a drop of open circuit voltage. It has been shown that recombination through deep levels in the QOs begins to dominate over recombination in the matrix at lower number of QOs layers than that through band-to-band recombination.

Effect of structural and temperature variations on perovskite/Mg2Si based monolithic tandem solar cell structure

Perovskite being a wide bandgap material has shown profound impact as an active material for the use of top cell in the tandem solar cell. However, finding a suitable low-bandgap material for the bottom cell of the perovskite associated tandem solar cell has always been a concern for researchers. Over the last decade, several materials for designing of the bottom cell have been reported as a combination to perovskite for superior efficiency. In this paper, a novel perovskite/Mg2Si based monolithic tandem solar cell is reported through numerical simulations using AFROS-HET v2.5. The reported device shows 25% efficiency prior to optimization. However, the structure of the device has been optimized to obtain better results in terms of efficiency by varying active layer thickness and using different electron/hole transport materials. About 8% improvement in efficiency has been noticed by the selection of optimum design parameters. Further, to account for the temperature reliability of the proposed design, the device is simulated for a temperature range of 300 K–450 K. This study highlights a drop-in open-circuit voltage (VOC) by a factor of about 0.1 V with an increase in temperature by about 50 K. Results clearly establish that structural and temperature variations significantly affect overall device performance. Results have been suitably analyzed so as to set a roadmap for further research work in this direction and explore the best of the characteristics of this unique tandem solar cell structure.

The Influence of the Number of Rows of GaInAs Quantum Objects on the Saturation Current of GaAs Photoconverters

The electroluminescence spectra and the dependences of the open circuit voltage on the photogenerated current are studied for GaAs solar cells the p–n junction of which contained various numbers of rows (r) of quantum objects based on In0.4Ga0.6As layers. For all samples, the saturation current (J0), the band gap of the quantum object ( $$E_{g}^{Q}$$ ), and the open circuit voltage drop (ΔVoc) relative to the reference (r = 0) sample are obtained. A model adequately describing the dependences J0(r) and ΔVoc(r) is proposed, and the model parameters are found, including the current invariant Jz = 1.4 × 105 A/cm2, which uniquely relates the saturation current to the band gap of the quantum object.

Nanophotonic Emission Control for Improved Photovoltaic Efficiency

With the necessary transition to renewable energy at hand, there is a renewed research focus on increasing solar cell efficiency, in order to reduce the cost of electricity. Nanomaterials are promising candidates to contribute to a new generation of low cost and highly efficient solar cells. Due to their wavelength-scale dimensions, nanomaterials display exceptionally strong light-matter interactions that lead to large perturbations in absorption and emission compared to their bulk counterparts. Although most work on nanostructured solar cells has focused on increasing the absorption, emission control may have even greater potential for improving efficiency of state-of-the-art solar cells. In this perspective article, we describe how nanostructures can be applied to improve solar cell efficiency, focusing on emission control. First, we analyze the requirements for making the most efficient solar cell, by looking at the thermodynamics of energy conversion. We show that an ideal solar cell at open circuit displays emission that is identical to its absorption. Comparing this to the emission of a typical silicon solar cell shows that there are three differences: the intensity, the angles in which light is emitted, and the spectrum. These differences lead to a reduction in efficiency, mainly due to a drop in open circuit voltage. For each loss mechanism, we discuss how nanomaterials can manipulate the emission and thereby reduce the voltage loss. Finally, we analyze the performance of two conceptual designs for solar cells based on nanomaterials. These give a large improvement in efficiency compared to conventional designs, showing the great potential of nanomaterials in solar cells.

Влияние числа рядов GaInAs-квантовых объектов на ток насыщения GaAs-фотопреобразователей

Electroluminescence spectra and the open circuit voltage vs photogenerated current characteristics for GaAs solar cells with different number of rows (r) of In0.4Ga0.6As quantum objects have been studied. For all samples with quantum objects, saturation current (J0), quantum object energy gap ), and the open circuit voltage drop (ΔVoc) have been obtained. A model is proposed that adequately describes the J0 – r and ΔVoс – r dependences. The model parameters have been found, including the current invariant Jz=1.4∙105 A/cm2, which uniquely connects the solar cell saturation current and a quantum object energy gap.

Comparative study of thermal runaway and cell failure of lab-scale Li-ion batteries using accelerating rate calorimetry

The safety of Li-ion batteries (LIBs) has long been a critical issue for their widespread application. The ever-increasing requirements for large-scale applications such as electric vehicles and stationary energy storage systems have spurred great interest in ensuring high standards of safety, which requires an understanding of the thermal runaway features of cells and modules. In this study, we evaluated the thermal runaway of pouch-type LIB cells with cell capacities of 33–3300mAh by using accelerated rate calorimetry (ARC) and lab-made hotbox ramping measurements. The large-capacity cells (1000 and 3300mAh) exhibited distinct stage behaviors of the self-heating rate in the ARC profiles and large exothermic reactions accompanied by an abrupt open-circuit voltage drop (internal short circuit) in the ramping test. The small-capacity cell (33mAh) showed an incomplete thermal runaway feature. These findings were attributed to the large proportion of inactive components relative to the active components, which is discussed in terms of the heat capacity. The data sensitivity factor is also suggested as a reliable measure of thermal runaway evaluation of LIB cells.

Initial photo-degradation of PCDTBT:PC70BM solar cells studied under various illumination conditions: Role of the hole transport layer

Encapsulated organic solar cells often show a burn-in behaviour under illumination. This burn-in manifests itself as a rapid performance loss followed by a much slower progression of the degradation. Here we investigate the burn-in for PCDTBT:PC70BM solar cells under a wide range of illumination intensities. We find that increasing the sunlight concentration from 1 Sun to up to 100 Suns does not change the degradation behaviour, i.e. the dependence of all principal photovoltaic parameters on the dose of solar exposure (in Sun hours). This suggests that the degradation mechanisms under solar concentration (≤100 Suns) are the same as those observed under 1 Sun. This result makes it possible to use concentrated sunlight for accelerated stability assessment of these devices. We also find that devices with PEDOT:PSS as hole transport material show a rapid drop in open-circuit voltage of around 100 mV during the first Sun hour of light exposure. By replacing PEDOT:PSS with MoO3 this initial process can be prevented and only the much slower part of the photo-degradation takes place.