Degradation Of Open Circuit Voltage Research Articles

Investigation into fill factor and open-circuit voltage degradations in silicon heterojunction solar cells under accelerated life testing at elevated temperatures

There are many reports on open-circuit voltage (VOC) degradation but limited reports on fill factor (FF) degradation in silicon heterojunction (SHJ) solar cells which are either subjected to an accelerated testing condition or to a field condition. The factors contributing to FF loss and VOC loss due to aging required a thorough investigation to gain insight into potential loss mechanisms and the approaches to mitigate them. In this context, we subjected SHJ solar cells of the same structure to varying accelerated testing conditions (i.e. exposure temperature of 90 °C versus 120 °C, under 1-sun illumination) in experiment 1 to 3 of this work. The SHJ cells exposed to a temperature of 90 °C were nearly stable in performance even after 2000 h while those exposed to 120 °C degraded significantly in FF. Device measurements and analysis revealed that the FF degradation was due to an increase in series resistance (Rs) and hole collection barrier. In experiment 4, the effect of device structure was investigated by subjecting cells with only front-side indium tin oxide (ITO) and those with both-sides ITO to the same accelerated testing conditions at a temperature of 90 °C under 1-sun illumination. The result obtained revealed that SHJ cells with both sides ITO were nearly stable in electrical performance while those with only front ITO degraded in performance, dominated by VOC loss. The VOC loss was perhaps due to loss of passivation at the rear-side of the cells.

Short Wavelength Photons Destroying Si–H Bonds and Its Influence on High‐Efficiency Silicon Solar Cells and Modules

Photons of varying wavelengths exert substantial effects on silicon heterojunction (SHJ) solar cells. Collaborative research previously establishes that light soaking with long‐wavelength photons can activate boron doping in hydrogenated amorphous silicon (a‐Si:H), thereby augmenting cell efficiency (Eff). Herein, this investigation is extended, exploring the effects of short‐wavelength photons on a‐Si:H layers, SHJ solar cells, and modules. The ultraviolet A (UVA) light with the wavelengths peak of 365 nm can disrupt Si–H bonds, resulting in a notable reduction in hydrogen content within both intrinsic and doped a‐Si:H films, and the deterioration of deteriorated interface passivation. Following exposure to 60 kWh m−2 of UVA light, both Eff and module power output decrease significantly, primarily attributable to the degradation of open‐circuit voltage and fill factor. As a feasible solution, the application of a light‐soaking process or the implementation of UV band cutoff module encapsulants can effectively mitigate the loss induced by UV irradiation, thereby ensuring the long‐term operation of SHJ solar cells and modules. Herein, a deeper understanding of UV‐induced performance changes in a‐Si:H film and its degradation mechanism for SHJ solar cells are contributed to in this research and also a viable strategy is provided to counter UV‐induced degradation.

Hydrogen-induced degradation dynamics in silicon heterojunction solar cells via machine learning

Among silicon-based solar cells, heterojunction cells hold the world efficiency record. However, their market acceptance is hindered by an initial 0.5% per year degradation of their open circuit voltage which doubles the overall cell degradation rate. Here, we study the performance degradation of crystalline-Si/amorphous-Si:H heterojunction stacks. First, we experimentally measure the interface defect density over a year, the primary driver of the degradation. Second, we develop SolDeg, a multiscale, hierarchical simulator to analyze this degradation by combining Machine Learning, Molecular Dynamics, Density Functional Theory, and Nudged Elastic Band methods with analytical modeling. We discover that the chemical potential for mobile hydrogen develops a gradient, forcing the hydrogen to drift from the interface, leaving behind recombination-active defects. We find quantitative correspondence between the calculated and experimentally determined defect generation dynamics. Finally, we propose a reversed Si-density gradient architecture for the amorphous-Si:H layer that promises to reduce the initial open circuit voltage degradation from 0.5% per year to 0.1% per year.

TOPcon route with quantum wells in GaInP/Si dual junction cell for efficiency enhancement

The GaInP/Si dual junction solar cell with Quantum Well and TOPCon technology has achieved 41.91 % efficiency in the simulation model. Quantum wells are proven to enhance the short circuit current without any significant degradation of open circuit voltage. The voltage preservation measure (for minimum reduction in open circuit voltage) is applied in design of Quantum well solar cell with the improvement in short circuit current, therefore the overall efficiency of dual junction cell is enhanced. In this work, the GaInP/Si dual junction solar cell is proposed by incorporating the InP quantum wells in the p-i-n region of GaInP top cell. Also, the TOPCon technology is applied at the rear side of the bottom c-Si solar cell. The quantum well increases the absorption of sub-bandgap photon energy. The buffer layer reduces the misfits between the lattice mismatched layers and tunnel oxide provides excellent passivation mechanism to increase the open circuit voltage. The ultrathin oxide layer provides extremely high electric field as described by the MIS tunneling theory. The electron and hole bound state energy and wavefunctions provides “miniband” formation and charge carrier trapping. The formation of type-A band structure in quantum well region and excellent electron mobility results in enhanced carrier transport. The GaInP/Si integrated model achieves efficiency of 33.30 % when the quantum wells are incorporated in the top cell. When the Combination of both QWs (in top cell) and TOPCon technology (in bottom cell) is applied, the model achieves 41.95 % efficiency. This model provides an excellent route toward achieving the 45 % efficiency limit of III-V/Si dual junction 2-terminal solar cell. The industry standard Silvaco TCAD platform is used for the calculation of the performance characteristics in AM1.5G environmental condition.

Analytical Model of InP QWs for Efficiency Improvement in GaInP/Si Dual Junction Solar Cell

Quantum wells (QWs) are proven to enhance the short circuit current and voltage preservation measures help in efficiency enhancement with little degradation of open circuit voltage . Herein, an integrated GaInP/Si dual junction solar cell is proposed by incorporating the QWs in the top cell and carrier‐selective passivated contact at the bottom cell of the design. The QW increases the photon absorption of sub‐bandgap energies, buffer layer reduces the misfits between the lattice mismatched layers, and passivation mechanism improves the overall efficiency. Increasing the number of QWs increases the depletion width of QW region. This reduces the carrier lifetime () and increases the recombinations in the QW region. It results in the reduction in passivation quality and, therefore, reduces the open circuit voltage (). QW strain balancing and measures to reduce the threading dislocations has been considered. Also, the wide bandgap GaInP tunnel junction along with highly doped GaAs tunnel junction has been analyzed to observe the parasitic effect. The GaInP/Si‐integrated model achieves efficiency of 33.39% when the QWs are incorporated in the top cell. The effect of wide bandgap tunnel junction is also evaluated using GaInP tunnel junction.

Open-Circuit Voltage Degradation by Dye Mulliken Electronegativity in Multi-Anchor Organic Dye-Based Dye-Sensitized Solar Cells

Open-Circuit Voltage Degradation by Dye Mulliken Electronegativity in Multi-Anchor Organic Dye-Based Dye-Sensitized Solar Cells

Analysis of Open Circuit Voltage Decay in Titanium Dioxide Electrode

Titanium Dioxide (TiO2) has been studied for its important photocatalytic semiconductor characteristics. Among many applicable areas of TiO2 photocatalysts, we have been studying to use as an anode electrode of the marine wet solar cells or marine microbial fuel cell. These studies include the analysis of TiO2 electrode prepared by the screen-printing method, and also the dye sensitizing effect on TiO2 electrode. In those studies, it was noticed that there is an open circuit potential that shifted to noble direction after TiO2 electrode was irradiated by the light source. This phenomenon usually occurred after a few minutes the electrode showed its photocatalytic characteristics. It is unclear which caused voltage loss during the measurement. In this study, we have been trying to understand the mechanism affecting the voltage decay of the TiO2 electrode and the factors influencing this.The TiO2 electrodes were prepared by screen printing method. Type 329J4L stainless steel which exhibits duel phase properties was used as a base substrate for the electrode. Firstly, the surface of the substrate was polished by sandpaper and the substrate was cleaned with acetone using the ultrasonic cleaner for 10 minutes. Then, the substrate was passivated with 10% nitric acid (HNO3) solution at 60 ºC for 30 minutes. After that, the substrate was screen printed with TiO2 paste followed by heat treating for 60 minutes and the first layer of TiO2 was formed. For the second layer forming, the substrate was again screen printed with TiO2 paste and heat treated for 30 minutes. With these processes, double-layered heterojunction TiO2 electrode was prepared. The electrode was then coated with insulating epoxy resins and prepared ready for the electrochemical measurements and analysis.The electrochemical measurements of TiO2 electrodes were performed in an artificial seawater used as an electrolyte. The irradiation was carried out on the electrodes using a calibrated xenon lamp with 150 W (wavelength ranging from 250 nm to 800 nm). The lamp was set to produce an output light intensity of 10.5 mW/cm2. The saturated calomel electrode (SCE) was used as the reference electrode. During the photo potential measurement, the potentials dropped as the electrodes were exposed to the light irradiation. But the potential values were ennobled after a few minutes the electrode was irradiated. Preliminary examinations showed that there is a relation between the ennobled potential values (open circuit voltage loss when coupled with a counter electrode) and the heat treatment temperatures of the electrodes. For example, the rebound rate of the photo-potentials of the electrode with heat treatment temperature of 150 ºC (second layer) was higher and longer compared to that of the electrode with 550 ºC (second layer). Detailed mechanism was yet under investigation. Those investigation includes the photopotential measurement and the electrochemical impedance spectroscopy (EIS). The surfaces of the electrodes before and after the measurements were compared and checked using scanning electron microscope (SEM). The X-ray powder diffraction (XRD) analysis and differential thermal analysis (DTA) were also included for analysis of the mechanism on the TiO2 electrode. The results of those analyses and the mechanism affecting the open circuit voltage degradation in the TiO2 electrode will be presented to the upcoming ECS conference.

Electron Irradiation Effects and Defects Analysis of the Inverted Metamorphic Four-Junction Solar Cells

The degradation of inverted metamorphic four-junction (GaInP/GaAs/In0.3Ga0.7As/In0.58Ga0.42As, IMM4J) solar cells irradiated by 1-MeV electrons was investigated via their spectral responses and the characterization of their electrical properties. As in the case of traditional three-junction (TJ) GaInP/GaAs/Ge solar cells, the electrical properties ( I sc, V oc, and P max) decrease with the logarithmic change of the electron fluence. The degradation of open-circuit voltage ( V oc) is slightly more pronounced than that of I sc in IMM4J solar cells because of the sum rule for V oc and the limit rule for I sc. The spectral response analysis showed that an In0.3Ga0.7As subcell was the most damaged subcell in the irradiated IMM4J solar cell, but an In0.58Ga0.42As subcell had the lowest initial short-circuit current density (Jsc), which was maintained throughout the irradiation test. We therefore focused on the In0.58Ga0.42As subcell. Deep-level transient spectroscopy (DLTS) experiments were realized to study emission and capture processes in two special full configurations of In0.58Ga0.42As and In0.3Ga0.7As subcells of the IMM4J solar cell. DLTS measurements reveal a dominant electron trap at 0.52 eV below the conduction band (Ec) of In0.58Ga0.42As, and the electron trap gradually evolved into Ec-0.46eV and Ec-0.58eV after 1-MeV electron irradiation. Based on the first-principles calculation, Ec-0.46 eV and Ec-0.58 eV can be assigned as ${\bf V}_{{\bf Ga}}^{\bf 0}/{\bf V}_{{\bf Ga}}^{{\rm{ - }}1}$ and ${\bf V}_{{\bf In}}^{\bf 0}/{\bf V}_{{\bf In}}^{{\bf - 1}}$ , respectively. However, only one shallow level Ec-0.03eV was observed within the bandgap of In0.3Ga0.7As after irradiation with DLTS detection. We summarize the issues faced for the space application of IMM4J solar cells by comparing the spectral responses of IMM3J, IMM4J, and TJ solar cells. Finally, the optimization of the design and fabrication of IMM solar cells are proposed.

Influence of plasma process on III-V/Ge multijunction solar cell via etching

In this paper, the impact of the plasma process for III-V/Ge heterostructure etching on both the morphology and the photovoltaic performance is investigated for the fabrication of multijunction solar cells with a through cell via contact architecture. Three different plasma chemistries (BCl3/Cl2, SiCl4/Cl2, and SiCl4/H2/Cl2) have been studied in order to obtain anisotropic etching through the multijunction heterostructure without inducing photovoltaic performance loss. SiCl4-based plasma chemistries have been found more suitable to achieve deep via hole etching (∼ 30 µm) without lateral etching. The study suggests that SiClx passivation is more efficient to protect the sidewalls compared to BClx. The addition of H2 in SiCl4/Cl2 mixture appears to reinforce the sidewall passivation and thus to limit the lateral etching. III-V/Ge triple junction solar cells with standard grid line and busbar front and back contact have been fabricated on which shallow via-holes have been etched in order to assess the associated photovoltaic performance loss to each plasma etching process. Despite the fact that similar hole sidewall profiles are obtained, the electrical performances are plasma chemistry dependant. This study demonstrates that the SiCl4/H2/Cl2 process presents the lowest losses with almost no induced open-circuit voltage degradation, which makes it promising for the through cell via contact architecture recently proposed for concentrated photovoltaics (CPV) solar cells.

Degradation of up-grown metamorphic InGaP/InGaAs/Ge solar cells by low-energy proton irradiation

To gain higher efficiency than that of traditional lattice-matched solar cells, newly designed up-grown metamorphic (UMM) InGaP/InGaAs/Ge solar cells were grown on Ge substrates. The defects in UMM InGaP/InGaAs/Ge can be perfectly controlled, and thus the conversion efficiency exceeds 30%. Similarly, the radiation environment in space could also cause displacement damage in UMM solar cells, causing the degradation of electrical properties. Proton irradiation at 50 keV and 150 keV was tested on the UMM solar cells. Because the top InGaP layer is thick enough, the radiation defects are limited within the top subcell without affecting the underlying subcells. In this research, 50-keV protons cause more serious degradation of short-circuit current, whereas 150-keV protons cause more serious degradation of open-circuit voltage. The difference may be related to the distribution of defects, which is calculated by The Stopping and Range of Ions in Matter (SRIM). Defects in the junction region would cause the decrease in voltage, whereas defects in the surface region could cause degradation of current. As a comparison, lattice-matched GaInP/GaAs/Ge solar cells were also irradiated by low-energy protons. The degradation under 150-keV protons is more serious because the damage peak lies in the middle GaAs layer, which has poor radiation resistance. The degradation under 70-keV proton irradiation proves that a thinner GaInP layer improves the radiation resistance. It is notable that the degradation of short-circuit current and maximum power is influenced by the equivalent displacement damage dose (DDD), but this is not accurate for open-circuit voltage. The artifact signals at 700–750 nm after 50-keV proton irradiation indicate the decrease in shunt resistance of the InGaP subcell during proton irradiation.

The interface modification for GNWs/Si Schottky junction with PEI/PEIE interlayers

Polyethylenimine ethoxylated (PEIE) and polyethyl-enimine (PEI), the two kinds of interface buffer layer, are widely used in the organic light-emitting diodes and solar cells for band alignment adjustment. In this report, we carefully studied the influence of the inserting organic layer on the graphene nanowalls(GNWS)/Si junction quality and the photoresponse of the Schottky devices. We found that thinner layers of PEI could decrease the dark current and improve the photo-to-dark ratio to 105 for n-Si devices. The s-kink effect and degradation of open circuit voltage could be observed for thicker thickness and excessive doping. Relatively, PEIE with stable thin layer not only improve the rectifying characteristics of p-Si devices but also the incident photon conversion efficiency. The maximus IPCE could reach 44% and be adjusted to zero by the reverse bias. The tunneling inhibition for electrons can be alleviated by increasing the barrier height. Our results provide an attractive method to improve the efficiency of pristine GNWs/Si junction with interface doping and passivation.

Power Conversion Efficiency and Device Stability Improvement of Inverted Perovskite Solar Cells by Using a ZnO:PFN Composite Cathode Buffer Layer.

We have demonstrated in this article that both power conversion efficiency (PCE) and performance stability of inverted planar heterojunction perovskite solar cells can be improved by using a ZnO:PFN nanocomposite (PFN: poly[(9,9-bis(3'-(N,N-dimethylamion)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctyl)-fluorene]) as the cathode buffer layer (CBL). This nanocomposite could form a compact and defect-less CBL film on the perovskite/PC61BM surface (PC61BM: phenyl-C61-butyric acid methyl ester). In addition, the high conductivity of the nanocomposite layer makes it works well at a layer thickness of 150 nm. Both advantages of the composite layer are helpful in reducing interface charge recombination and improving device performance. The power conversion efficiency (PCE) of the best ZnO:PFN CBL based device was measured to be 12.76%, which is higher than that of device without CBL (9.00%), or device with ZnO (7.93%) or PFN (11.30%) as the cathode buffer layer. In addition, the long-term stability is improved by using ZnO:PFN composite cathode buffer layer when compare to that of the reference cells. Almost no degradation of open circuit voltage (VOC) and fill factor (FF) was found for the device having ZnO:PFN, suggesting that ZnO:PFN is able to stabilize the interface property and consequently improve the solar cell performance stability.

Numerical simulation of silicon heterojunction solar cells with Si/Si1-xGex quantum wells

Heterojunction with intrinsic thin-layer (HIT) solar cells attract attention due to their high open circuit voltage and stable performance. However, short circuit current density is difficult to improve due to light losses of transparent conductive oxide and hydrogenated amorphous silicon passivation (a-Si:H) layer and low absorption coefficient of crystalline silicon (c-Si). Silicon germanium alloy (Si/Si1-xGex) quantum wells and quantum dots are capable of improving low light utilization by strong optical absorption in the infrared region. In this article, opto-MoS2of the HIT solar cells integrated with Si/Si1-xGex quantum wells (HIT-QW) as a surface absorber are investigated by numerical simulation with Technology Computer Aided Design (TCAD). The influences of germanium content on the MoS2of HIT solar cells with long carrier lifetimes of Si1-xGex layers (p*) and defect-free a-Si:H/c-Si interface are investigated at first. The simulation results indicate that optical utilization in the infrared region is enhanced with the increase of germanium fraction, while open circuit voltage degrades due to the decreasing of the energy band gap of Si1-xGex, radiative recombination and auger recombination mechanism in the Si/Si1-xGex quantum wells. And the conversion efficiency reaches a maximum value at a germanium fraction of 0.25 then drops distinctly. When the germanium fraction increases from 0 to 0.25, the short circuit current density increases from 34.3 mA/cm2 to 34.8 mA/cm2, while the open circuit voltage declines from 749 mV to 733 mV. Hence, the conversion efficiency increases from 21.5% to 21.7% due to the fact that the enhancement of short circuit current density compensates for the reduction of open circuit voltage. When the germanium content increases to more than 50%, a serious open circuit voltage loss of more than 130 mV associated with the energy band gap loss of Si1-xGex arises in the HIT-QW solar cells, which indicates that the dominating carrier transport mechanism changes from shockley diffusion to recombination in the Si/Si1-xGex quantum wells. Subsequently, the influences of interface defects at a-Si:H/c-Si interface and bulk recombination centers in the Si/Si1-xGex quantum wells are discussed. Both interface holes at a-Si:H/c-Si interface and bulk holes in Si1-xGex quantum wells can be recombined through the interface defects at a-Si:H/c-Si interface and bulk recombination centers in the Si/Si1-xGex quantum wells, respectively, which restricts the position of hole fermi level in the open circuit condition. When the germanium fraction increases, the influence of interface defects at a-Si:H/c-Si interface becomes weak on the degradation of open circuit voltage compared with the significant influence of the bulk trap centers. Moreover, p* of longer than 510-5 s is necessary for the retention of electrical performance of HIT-QW solar cells by the simulation. Based on this research, high-efficiency HIT solar cells can be achieved by incorporating high-quality Si/Si0.75Ge0.25 quantum wells, which also requires the impactful passivation of a-Si:H/c-Si interface.

The study of the carriers’ transport mechanism of GaAs/Ge solar cells based on irradiation damage model

Based on the irradiation damage model of solar cells, the irradiation damage mechanism of space solar cells from the aspect of the carriers’ transport is studied. The basic rules of electrical parameter degradation of GaAs/Ge solar cells under different energy proton and electron irradiation are obtained through the ground-accelerated equivalent simulation test for space-charged particles. The open-circuit voltage degradation curves of the solar cells are fitted nonlinearly by its mathematical model. The change laws of damage coefficient of majority carriers’ removal rate with the incident proton and electron energy are given. The damage coefficient of GaAs/Ge solar cells first increases and then decreases with increasing incident proton energy, and it reaches a maximum at 100keV proton irradiation. In addition, the damage coefficient increases with increasing incident electron energy. The studies show that open-circuit voltage degradation is closely related to the removal effect of the majority carriers under charged particle irradiation. The results have important significance to reveal the irradiation damage mechanism of the space solar cells.

Photovoltaic Platform for Investigating PV Module Degradation

Photovoltaic research is oriented more and further towards study on PV modules degradation. The objective is to understand the different degradation modes of PV modules and associated factors. This paper presents a platform for measures dedicated to do a study related to degradation of electrical characteristics of the photovoltaic modules. It is installed on the site at University of Dakar in Senegal. This work proposes a method for standardization of the direct measures of the short-circuit current (Isc) and the open-circuit voltage (Voc) of PV modules. The approach used for the assessment of degradation of Isc and Voc involves a comparison between baseline values given by manufacturer and those measured in real operating conditions brought back in the standard test conditions (STC). Findings presented on degradation of Isc and Voc photovoltaic modules cover the first ten months of measurements from Mars to January. Degradation of short-circuit current is about 13% for the three days. The degradation of open-circuit voltage measured during the three days is 8%.

Novel fluoride-doped barium cerate applied as stable electrolyte in proton conducting solid oxide fuel cells

Exploring chemically stable and high proton conductive electrolyte materials is a key to develop commercial solid oxide fuel cells operating at intermediate temperatures. BaCeO3 based oxides show good proton conductivity at intermediate temperatures; nevertheless, their large Brønsted basicity makes them prone to react with acidic gases such as CO2, and thus, chemically unstable in the operating atmospheres of SOFCs. This problem largely hampers the practical application of these oxides. In this work, we report a new strategy to reduce the basicity of BaCeO3 based oxides by using F−, with higher electronegativity, to partially substitute for O2− ions. The new compound of F-doped BaCe0.8Sm0.2O2.9 (BCSF) has demonstrated significant improved chemical stability in CO2 containing atmosphere with no loss of proton conductivity. With a 39μm-thick BCSF electrolyte, the peak power density of single cell was 420mWcm−2 at 700°C in humidified H2/air system, approximately 20% higher than that using a BaCe0.8Sm0.2O2.9 electrolyte. Especially, within a 146h test, negligible degradation in open circuit voltage (OCV) was observed using our new BCSF electrolyte.

Elimination of burn-in open-circuit voltage degradation by ZnO surface modification in organic solar cells.

Photodegradation of inverted organic solar cells based on ZnO as an electron transport layer (ETL) was studied over short time scales of 5 min and 8 h. Devices with ZnO as ETL reproducibly exhibited a steep loss of open-circuit voltage, VOC, and shunt resistance, RSH, in a matter of minutes upon illumination. Removing the UV-content of illumination minimized VOC loss and impact on the device's shunting behavior, indicating its role in the loss. Application of an ultrathin layer of Al on ZnO led to almost negligible photoinduced VOC loss up to 8 h of exposure. By applying the fundamental Shockley diode equation, we approximated the VOC loss to be caused by dramatic increases in reverse saturation current I0. We attribute the increased rate of recombination to diminished carrier selectivity at the ZnO/organic interface. Devices with Al modified ZnO ETL demonstrated remarkable RSH (1.4 kΩ cm(2) at 1 sun), rectification ratio (10(6)) and reverse saturation current density (2.1 × 10(-7) mA/cm(2)).

Two-Dimensional Modeling of the Metallization-Induced Recombination Losses of Screen-Printed Solar Cells

We present an approach of implementing the experimental microscopic observations at metal-Si emitter interface into a 2-D simulation model to investigate the metallization-induced recombination losses of crystalline Si solar cells with firing through metallization. This metal-Si interface is typically characterized by few Ag crystallites grown into Si, whereas the main part of the interface area is covered by a glass layer. By using this simulation model, we were able to disentangle the effect that each of these microscopic features has on solar cell performance. The model assumes the metal-Si interface to be either Ohmic or Schottky, with current extraction occurring only through the direct Ag crystallites-Si interface. The simulation results show negligible degradation in open-circuit voltage (V OC ) and pseudo-fill factor (pF F) if the metal-Si interface comprises the sole presence of Ag crystallites, as long as these crystallites grow only superficially and are not penetrating the p-n junction. A more detrimental effect is observed if the emitter area beneath the glass layer is affected by etching. For more aggressive metallization pastes or for overfiring scenarios where larger in-grown crystallites are observed that are protruding through the p-n junction, the model assuming a Schottky contact qualitatively explains the shunting behavior observed experimentally.

Improve the operational stability of the inverted organic solar cells using bilayer metal oxide structure.

Operational stability is a big obstacle for the application of inverted organic solar cells (OSCs), however, less talked about in the research reports. Due to photoinduced degradation of the metal oxide interlayer, which can cause shunts generation and degeneration in ZnO interlayer, a significant degradation of open circuit voltage (Voc) and fill factor (FF) has been observed by in situ periodic measurements of the device current density-voltage (J-V) curves with light illumination. By combining TiOx and ZnO to form bilayer structures on ITO, the photovoltaic performance is improved and the photoinduced degradation is reduced. It was found that the device based on ZnO/TiOx bilayer structure achieved better operational stability as compared to that with ZnO or TiOx interlayer.

High performance Ni–Fe alloy supported SOFCs fabricated by low cost tape casting-screen printing-cofiring process

Novel Ni–Fe alloy supported solid oxide fuel cells, with Ni cermet as functional anode, La0.8Sr0.2MnO3 coated Ba0.5Sr0.5Co0.2Fe0.8O3 as cathode and Gd-doped Ce2O3 as electrolyte, are successfully fabricated by the cost effective method of tape casting-screen printing-cofiring. The Ni–Fe porous substrate is obtained by reduction (in H2 at 650 °C for 2 h) of sintered NiO-10 wt% Fe2O3 consisting of NiO and NiFe2O4. The cell is subjected to evaluation in the aspects of electrochemical performance and redox capability at temperatures between 500 and 650 °C. The result shows a peak power density of 1.04 W cm−2 at 650 °C. Furthermore, the metal support cell exhibits excellent tolerance to redox cycles. Five redox recycles for cells are operated at 600 °C, which shows no significant degradation in open circuit voltage and power density.