Potential Induced Degradation Research Articles

Application of SiOxNy films in industrial bifacial PERC solar cells

The bifacial p-type silicon (p-Si) passivated emitter and rear cells (PERCs) have dominated the industrial bifacial solar cells. In this paper, we have investigated the impact of hydrogenated amorphous silicon oxynitride (SiOxNy) films on the optical and electrical performance of bifacial p-Si PERCs. Simulation and characterization are carried out to show the improvement of bifacial p-Si PERCs, yielding an absolute front-side efficiency improvement of 0.14% and 016% with SiOxNy films introduced to the front-side and rear-side, respectively. When SiOxNy films are employed to both sides of bifacial p-Si PERCs, the front-side and rear-side efficiency separately increase by 0.27% and 0.26% compared to the baseline without SiOxNy films. We have achieved on the bifacial p-Si PERCs production line an averaged front-side efficiency of 23.23% (champion efficiency of 23.42%), together with a 17.31% averaged rear-side efficiency. Furthermore, the introduction of SiOxNy films has been demonstrated to reduce the rear-side potential induced degradation (PID) effect through both single-cell modules and commercial glass-glass modules, due to the SiOxNy films protecting AlOx from corrosion and maximizing the field-effect passivation of AlOx layers.

Impact of Potential‐Induced Degradation on Different Architecture‐Based Perovskite Solar Cells

Organic–inorganic perovskites photovoltaic materials are considered as one of the promising candidates for the emerging photovoltaic (PV) sector. It has drawn tremendous attention from fundamental research and PV industries, due to its high efficiency, chemical properties, and low fabrication cost. But, its lifetime under real field operation is always the major obstacle toward commercialization. Potential‐induced degradation (PID) is known as the common reliable threat in the established commercial PV technologies which lead to catastrophic failure within a short time. Thus, it is essential to enable reliability assessment of PID on the precommercial development stage of perovskite photovoltaics to further enrich the confidence by identifying, eliminating, and developing an understanding of the possible degradation mechanism in the field condition. In this article, different architecture‐based perovskite solar cells are studied to reveal the degradation mechanism under PID for the first time. The results show that PSCs of n–i–p with a phenyl C61 butyric acid methyl ester (PCBM) layer have good stability under PID compared with other treated structures with only 4% degradation after 18 h.

Suppression of potential-induced degradation in monofacial PERC solar cells with gradient-designed capping layer

The potential-induced degradation (PID) of p-type crystalline silicon passivated emitter and rear cell (PERC) is a critical issue causing severe output power loss. In this paper, a gradient-designed capping layer consisting of silicon nitride/silicon oxynitride/silicon oxide (SiNx/SiNxOy/SiOx) is proposed as the surface coating for p-type PERC solar cells. The capping layer improves the short wavelength spectral response due to its better anti-reflection effect. An impressive efficiency of 23.52% has been achieved on mass production line. A long-term PID evolution up to 672 h is performed for glass/back sheet PERC cell modules under stringent conditions with the ambient temperature of 85 °C, relative humidity of 85%, and the applied voltage of 1500 V. The current–voltage (light I-V, dark I-V) parameters of the modules were measured, as well as the electroluminescence, to evaluate the effect of sodium ion migration in PERC solar cells. It is shown that monofacial PERC solar modules suffer from shunt of PN junction under PID stress, which can be obviously suppressed by gradient-designed capping layers. The optimized PERC solar modules show excellent PID resistance, showing great potential for lower levelized cost of energy (LCOE) of photovoltaic power generation.

Characterization of Potential-Induced Degradation and Recovery in CIGS Solar Cells

The potential-induced degradation (PID) mechanism in Cu(In,Ga)(Se,S)2 (CIGS) thin-film solar cells, which are alternative energy sources with a high efficiency (>23%) and upscaling possibilities, remains unclear. Therefore, the cause of PID in CIGS solar cells was investigated in this study at the cell level. First, an appropriate PID experiment structure at the cell level was determined. Subsequently, PID and recovery tests were conducted to confirm the PID phenomenon. Light current–voltage (I–V), dark I–V, and external quantum efficiency (EQE) analyses were conducted to determine changes in the cell characteristics. In addition, capacitance–voltage (C–V) measurements were carried out to determine the doping concentration and width of the space charge region (SCR). Based on the results, the causes of PID and recovery of CIGS solar cells were explored, and it was found that PID occurs due to changes in the bulk doping concentration and built-in potential at the junction. Furthermore, by distinguishing the effects of temperature and voltage, it was found that PID phenomena occurred when potential difference was involved.

Cell-level reliability testing procedures for CIGS photovoltaics

The reliability of photovoltaics is commonly studied at the module level. Many reliability problems originate from module attributes, such as metal interconnections to cells, junction boxes. However, significant work in reliability can also be done prior to module design. Testing for reliability earlier in the research cycle increases the probability of avoiding common module reliability problems before cell changes are implemented on a large scale. Cell-level reliability studies can thus lower the rates of module failures in the field and provide confidence to investors that new technologies will perform as advertised. This report summarizes how we investigated three reliability concerns in Cu(In,Ga)Se2 (CIGS) photovoltaics at the cell level: metastability, shading-induced damage, and potential-induced degradation (PID). Examining these concerns required developing robust measurement protocols including the fabrication of novel testing structures. This information will allow readers to incorporate sound metrics for investigating reliability phenomena and aid their studies of cell and module reliability improvements.

Behavioral Analysis of Potential Induced Degradation on Photovoltaic Cells, Regeneration and Artificial Creation

Many photovoltaic (PV) parks suffer from a decrement in their generated power capability due to a phenomenon called potential induced degradation (PID). In this paper, a regenerative system using a high step-up DC–DC converter is proposed, for regenerating PV cells that have been degraded due to the PID effect. The same device also can be used for artificially creating PID on PV panels in order to study the effects of the PID under controlled conditions. The power converter offers multiple voltage levels at the output to adapt to various voltage ratings of PV parks. The device has plug-and-play features, ultra-low cost, small size and is simple in operation. Experimental tests are conducted in real PV panels and comparative results verify the operational principles of the proposed system. The artificial creation of the PID phenomenon and the regeneration of the PV cells are successfully proven experimentally.

Delamination-and Electromigration-Related Failures in Solar Panels—A Review

The reliability of photovoltaic (PV) modules operating under various weather conditions attracts the manufacturer’s concern since several studies reveal a degradation rate higher than 0.8% per year for the silicon-based technology and reached up to 2.76% per year in a harsh climate. The lifetime of the PV modules is decreased because of numerous degradation modes. Electromigration and delamination are two failure modes that play a significant role in PV modules’ output power losses. The correlations of these two phenomena are not sufficiently explained and understood like other failures such as corrosion and potential-induced degradation. Therefore, in this review, we attempt to elaborate on the correlation and the influence of delamination and electromigration on PV module components such as metallization and organic materials to ensure the reliability of the PV modules. Moreover, the effects, causes, and the sites that tend to face these failures, particularly the silicon solar cells, are explained in detail. Elsewhere, the factors of aging vary as the temperature and humidity change from one country to another. Hence, accelerated tests and the standards used to perform the aging test for PV modules have been covered in this review.

Influence of Light Irradiation on Potential-Induced Degradation for Thin-Film Si Photovoltaic Modules

Delamination observed for superstrate-type thin-film Si photovoltaic (PV) modules exposed outdoors was reproduced by indoor acceleration test with high-voltage application. Such delamination was observed for the PV modules left in the air after potential-induced degradation (PID) acceleration test and was a kind of PID. The delamination occurred near the interface between glass and transparent conductive oxide. In this study the origins of the delamination for thin-film Si PV modules were analyzed and the influences of light irradiation and humidity were also investigated. The delamination occurred only at the position with voltage application and high concentration of Na was detected at the delamination region. Delamination was also enhanced by high humidity. It also turned out that light irradiation delays both deterioration of PV performances and also the delamination by high-voltage application. However, PID behaviors are almost the same regardless of including UV component. This is much different from crystalline Si case that UV component is required for the PID delay.

Accelerated stress testing of potential induced degradation susceptibility of PV modules under different climatic conditions

Potential Induced Degradation (PID) is one of the severe failure modes observed in the field with high system voltage, high humidity and high operating temperature. PV module needs to be tested for PID susceptibility as per site conditions before installation in the field. In this paper the effect of temperature, humidity, and voltage on leakage current, as well as PID, has been analyzed for multi-crystalline silicon and HIT module technologies. Also, reported the effect of PID stress on PV modules in terms of electrical degradation and visual defects. For the studied multi-crystalline module, deviation of degradation between one cycle and three cycles of PID stress for the Isc is 98%, Voc is 18% and Pmax degradation is 87%. This paper also reported a case study about the designing of accelerated stress testing of the PID of the PV module for different climatic zones of India. The stress testing condition was designed at harsh conditions of temperature and humidity for representative sites of climatic zones. It was found that the required testing time for PV module in the case of Hot & humid climatic zone is more as compared to other climatic zones.

Photovoltaic module failures after 10 years of operation in the tropics

This paper presents a case study of photovoltaic (PV) module failures after over 10 years of operation in the tropical climate of Singapore. Three types of modules (two samples from each type) were analysed: multi-crystalline silicon (multi-Si), mono-crystalline silicon (mono-Si), and copper indium selenide (CIS). Visual inspection revealed several problems, including encapsulant discoloration (to different extents), backsheet yellowing, and soiling among others. Different degradation behaviour of the samples was observed from current-voltage (IV) and electroluminescence characterization. The maximum power of the multi-Si samples degraded by more than 9% (on average), likely due to corrosion around the cell edges. The mono-Si modules suffered a catastrophic power reduction (>40%) that could be ascribed to a combination of encapsulant discoloration, potential-induced degradation (PID), and corrosion. While one CIS module was primarily affected by encapsulant discoloration and possibly corrosion, the other sample also exhibited signatures of PID and experienced about 45% power drop. Furthermore, external quantum efficiency measurements of the multi-Si modules identified cell mismatch and changes to the additives in the encapsulant. Overall, PID, corrosion and encapsulant degradation are found to be the most detrimental degradation processes for PV modules in the tropical climate of Singapore.

Time‐Resolved Investigation of Transient Field Effect Passivation States during Potential‐Induced Degradation and Recovery of Bifacial Silicon Solar Cells

Various types of potential‐induced degradation (PID) with fundamentally different physical root causes have been observed recently ranging from shunting (PID‐s), corrosion (PID‐c) to degradation of surface passivation (PID‐p). Herein, PID‐p is investigated for the first time at the rear side of bifacial silicon solar cells with enhanced time‐resolution during degradation and recovery under simultaneous illumination. The tests reveal fast transient changes of rear‐side short‐circuit current within minutes and thus allow to understand the degradation process related to PID‐p. The short‐circuit current with rear‐side illumination first decreases significantly by more than 80 % resulting in an intermediate degraded state. Subsequently, it increases to a regenerated state. Under reversed bias, a total recovery of the cell parameters is observed and confirmed by I–V measurements under standard testing conditions (STCs). The underlying transient PID‐p degradation and recovery mechanism is well described by a PC‐1D simulation of the field‐induced band bending at the rear surface. Finally, a qualitative model involving the migration of mobile charged species and their impact on the charge equilibrium in the field effect passivation layer is presented. Thus, time‐resolved analysis of transient PID effects can serve as a clear characteristic for PID of polarization type.

Unraveling the cause of degradation in Cu(In,Ga)Se2 photovoltaics under potential induced degradation

AbstractCopper indium gallium diselenide (CIGS) based technology is actively competing in the global photovoltaic market with high conversion efficiency. Commercial CIGS modules are anticipated to perform on rated output in the field condition for 20 years. Potential induced degradation (PID) is considered as one of the critical concerns among all the current reliability assessment issues. PID accelerated tests have been performed on pre‐commercial CIGS modules to investigate reduction in electrical performance. We report the severe reduction in electrical performance after PID is correlated to the microstructural and chemical properties of the constituent materials. Under extreme PID stress, the cell surface reveals various defects including crater formation. The aim of this article is to explore the consequences of PID induced craters on the efficiency of CIGS solar cells by investigating material degradation kinetics. In this perspective, we present the root cause of PID in CIGS thin‐film modules in relation to microstructural defects by detailed investigation using J‐V analysis, field emission scanning electron microscope (FESEM), Raman spectroscopy, X‐Ray diffraction (XRD), X‐ray photoelectron spectroscopy (XPS) and photoluminescence spectroscopy (PL). This analysis can provide more effective and sustainable research strategies to cultivate more efficient and reliable CIGS technologies in the long run.

Diagnostics of PID Early Stage in PV Systems

Potential induced degradation (PID) is a serious threat for the photovoltaic (PV) industry. The risk of PID may increase with increasing operating voltage of PV systems. Although PID tests are currently standard tests, the expansion of floating PV power plants and installation in humid climates show that PID-free modules are still sensitive to this type of degradation. Therefore, a method that can detect PID in the initial phase before standard tests reveal it, is necessary to increase the reliability of PV systems and maintain their lifetime. One possible tool for revealing early-stage PID manifestations is impedance spectroscopy and I-V dark curves measurements. Both IS and dark current measurement methods are sensitive to cell shunt resistance (RSH), which is strongly influenced by PID before significant power loss and can act as an early stage PID detection mechanism. The paper describes the differences of the common P-type PV module parameters both during the degradation process and also during the regeneration process when diagnosed by conventional and IS and dark current measurement methods.

Bifacial Photovoltaics 2021: Status, Opportunities and Challenges

In this paper we summarize the status of bifacial photovoltaics (PV) and explain why the move to bifaciality is unavoidable when it comes to e.g., lowest electricity generation costs or agricultural PV (AgriPV). Bifacial modules—those that are sensitive to light incident from both sides—are finally available at the same price per watt peak as their standard monofacial equivalents. The reason for this is that bifacial solar cells are the result of an evolution of crystalline Si PV cell technology and, at the same time, module producers are increasingly switching to double glass modules anyway due to the improved module lifetimes, which allows them to offer longer product warrantees. We describe the general properties of the state-of-the-art bifacial module, review the different bifacial solar cells and module technologies available on the market, and summarize their average costs. Adding complexity to a module comes with the increase of possible degradation mechanisms, requiring more thorough testing, e.g., for rear side PID (Potential Induced Degradation). We show that with the use of bifacial modules in fixed tilt systems, gains in annual energy yield of up to 30% can be expected compared to the monofacial equivalent. With the combination of bifacial modules in simple single axis tracking systems, energy yield increases of more than 40% can be expected compared to fixed tilt monofacial installations. Rudimentary simulations of bifacial systems can be performed with commercially available programs. However, when more detailed and precise simulations are required, it is necessary to use more advanced programs such as those developed at several institutes. All in all, as bifacial PV—being the most cost-effective PV solution—is now becoming also bankable, it is becoming the overall best technology for electricity generation.

Effects of passivation configuration and emitter surface doping concentration on polarization-type potential-induced degradation in n-type crystalline-silicon photovoltaic modules

System voltages can cause significant degradation in photovoltaic modules. Polarization-type potential-induced degradation (PID) is accompanied by decreases in the short-circuit current density and the open-circuit voltage. The system voltage causes a polarization and surface charge accumulation, increasing the interface recombination. The surface passivation and the emitter doping concentration and gradient are considered to have large impacts. However, a systematic study on these effects has not yet been performed. In this paper, the effects of the front surface structure of n-type passivated emitter and rear totally diffused cell modules were investigated by accelerated PID tests. Standard cells with thin silicon dioxide/80-nm silicon nitride (SiNx) antireflection/passivation layers, refractive index (RI) of 2.0, exhibited typical polarization-type PID. Cells with increased RI = 2.4 for the bottom 20-nm SiNx showed no degradation at all. This may be caused by reduced charge accumulation in the SiNx layer near the interface due to the higher electrical conductivity of the Si-rich bottom layer. Secondly, cells with both a highly distorted interface, due to nitrogen insertion in the silicon surface, and an emitter with a high surface doping concentration have excellent resistance to PID. Cells with either the highly distorted interface or the higher emitter-surface doping concentration show no to minor improved resistance to PID. These findings improve the understanding of the effects of the front surface structure of cells on the polarization-type PID and may contribute to the implementation of these measures to reduce PID.

Influence of light illumination on the potential-induced degradation of n-type interdigitated back-contact crystalline Si photovoltaic modules

We investigate the potential-induced degradation (PID) of n-type interdigitated back-contact (IBC) crystalline Si (c-Si) photovoltaic (PV) modules under a negative bias stress and the influence of light illumination on the PID. IBC PV modules show PID characterized by a reduction in the short-circuit current density (J sc) and open-circuit voltage (V oc) under negative bias stress, while no fill factor (FF) reduction is observed. The degradation may originate from the introduction of sodium (Na) into c-Si and the resulting enhancement of carrier recombination on the surfaces of the IBC cells. Light illumination of 1 sun during the negative bias PID test results in less severe reductions of J sc and V oc. A reduction in the electric field on the surface Si nitride (SiN x ) film, due to carrier generation in the SiN x and the resulting increase in its conductivity, is a possible explanation for the mitigation of the Na-related PID.

Reduced power degradation in bifacial PERC modules by a rear silicon oxide additive layer

In this paper, we investigate the influence of silicon oxide (SiOx) layer on the potential induced degradation (PID) of P-type monocrystalline PERC cells and modules. A SiOx layer was added between the aluminum oxide (AlOx) and silicon nitride (SiNx) layers on the rear side of PERC cells using a newly designed plasma enhanced chemical vapor deposition (PECVD) tool, MAiA from Meyer Burger. The performance of cells and modules with this AlOx + SiOx + SiNx stack was characterized by electrical breakdown (EBD), cell degradation indicator (CDi) and climate chamber PID tests. The EBD test results indicate that the AlOx + SiOx + SiNx stack has higher breakdown voltage than the typically used AlOx + SiNx stack. After undergoing CDi tests, power degradation is more severe in PERC cells with AlOx + SiNx passivation stack than those with AlOx + SiOx + SiNx passivation stack, as evidenced by darker photoluminescence. Bifacial modules made from PERC cells with the AlOx + SiOx + SiNx rear passivation stack demonstrate a significant reduction in rear PID from 12.3% to 4.2%. The results above depict that the addition of a SiOx layer between the AlOx and SiNx layers could effectively reduce the transfer of positive charges from the SiNx layer into the AlOx layer.

Monitoring of Photovoltaic System Performance Using Outdoor Suns-VOC

Summary In-field characterization of photovoltaics is crucial to understand performance and degradation mechanisms, subsequently improving overall reliability and lifespans. Current outdoor characterization is limited by logistical difficulties, variable weather, and requirements to measure during peak production hours. We capitalize on Suns-VOC, which is widely used for laboratory measurements of single solar cells and discuss the barriers in extending the technique to outdoor systems. We demonstrate the normalization of measurements using both backsheet temperature sensors and on-site weather stations. Despite weather variation, VOC, ideality factor, and pseudo fill factor all fall within 1% of the laboratory measurements. It is also demonstrated that monitoring the system VOC at 0.05 to 0.1 suns, during minimal power production, provides a figure of merit that can indicate early degradation of the system. Extensive simulations show that shading portions of a system has minimal effect on measurements, allowing the technique to be used in all weather conditions.

Outdoor Implied Current–Voltage Measurements of an Individual Encapsulated Cell in a Module

The performance of solar cells influences the reliability, lifetime, cost, and safety of photovoltaic power plants. The electrical performance of these cells, as well as, their degradation rates over time, can vary between individual cells within the same photovoltaic module. Current-voltage measurements can provide detailed data on cell performance, however, it cannot be performed on individual cells in encapsulated modules. In this study, we propose a contactless and nondestructive method that is based on Suns-photoluminescence measurements to extract the current-voltage characteristics of individual solar cells under operating conditions in the field. Applications of the method to identify the extent of various degradation mechanisms, such as light-induced and potential-induced degradation, are demonstrated and discussed. The main advantages of the proposed method include its low cost, and its fast and easy applicability.

Electrical and Temperature Behavior of the Forward DC Resistance With Potential Induced Degradation of the Shunting Type in Crystalline Silicon Photovoltaic Cells and Modules

Potential-induced degradation (PID) is an unsolved and major power degradation mechanism that affects photovoltaic (PV) cells, and the tendency to increase the operating voltage of PV systems will render it worse, affecting their reliability. A method, which can detect PID at an early stage, can alleviate reliability issues, safeguarding high energy output. The measurement of the forward dc resistance (FDCR) provides promising results for the early PID detection (<;2% power loss). The FDCR method is tested on single-cell and multi-cell PV modules and it is the pathway for the development of a detection method at the system level. This work examines the effect of PID degradation rate and temperature on the detection sensitivity (electrical behavior) of the FDCR method. Additionally, the effect of temperature (temperature behavior) on the FDCR as PID progresses is studied. The electrical behavior demonstrates that the detection sensitivity is robust to PID degradation rate and temperature and that the degradation rate is not related to the initial shunt resistance of the PV cell. The temperature behavior indicates that the temperature coefficient of the FDCR is initially negative and increases toward more positive values as PID progresses. Furthermore, the electrical variation of the FDCR with PID progression is much higher (74%) than the variation of the FDCR due to temperature (19%) and this favors PID detection.