Potential-induced Degradation Test Research Articles

Potential-induced degradation phenomena in single-encapsulation crystalline Si photovoltaic modules

This paper particularly explains potential-induced degradation (PID) of wafer-based standard p-type crystalline silicon technology. We present a single-encapsulation method that is useful for simulating PID in the laboratory to facilitate microanalyses of module-level solar cells. The PID testing is performed for the module with single-encapsulation and conventional modules. Their current–voltage characteristics and electroluminescence images are investigated before and after the PID tests. As described herein, we infer that the single-encapsulation modules generate PID almost in the same way as conventional modules do, and that the degradation trend is almost identical to that of conventional modules. Results of PID recovery tests indicate that the time necessary for PID recovery is always less than that for PID generation, irrespective of the encapsulation method.

Delay of the potential-induced degradation of n-type crystalline silicon photovoltaic modules by the prior application of reverse bias

We investigated the influence of the pre-application of reverse bias on the potential-induced degradation (PID) of n-type front-emitter (n-FE) crystalline Si (c-Si) photovoltaic modules. Applying a prior positive reverse bias to n-FE cells delays charge-accumulation-type PID (PID-1), decreases in short-circuit current density (J sc) and open-circuit voltage (V oc). The prior positive bias accumulation may accumulate negative charges in the SiN x , which leads to an increase in a duration for the positive charge accumulation by the PID test applying a negative bias. We also found that sufficiently long prior positive bias application results in the delay of PID-2, a fill factor reduction by the incursion of Na ions into the depletion region of the p–n junction of n-FE cells.

Prevention of PID Phenomenon for Solar Panel Based on Mathematical Data Analysis Models

In recent years, the problem of potential-induced degradation (PID) phenomenon has been deeply associated with solar power issues because it causes serious power attenuation of solar panels and results in lowering its power generation efficiency. Thus, effectively identifying the PID problem from insights of industry data analysis to reduce production costs and increase the performance of power generation is an interesting and important subject for the solar power industry. Moreover, by the traditional standard rule (IEC62804) and the condition of a 96 h testing time, the costs of testing time and assembling materials against PID are very high and must be improved. Given the above reasons, this study proposes a hybrid procedure to organizes four mathematical methods: the mini-module testing, solar cell testing, a settling time, and a neural network, which are named as Method-1–Method-4, respectively, to efficiently solve the PID problem. Consequently, there are four key outcomes from the empirical results for solar power application: (1) In Method-1 with a 96 h testing time, it was found that the large module with higher costs and the mini module with lower costs have a positive correlation; thus, we can replace the large-module testing by the effective mini module for lower cost on module materials. (2) In Method-2 with a 24 h testing time, it was also found that the mini module and the solar cell are positively correlated; this result provides evidence that we can conduct the PID test by the easier solar cell to lower the costs. (3) In Method-3, the settling time achieves an average accuracy of 94% for PID prediction with a 14 h testing time. (4) In Method-4, the experimental result provides an accuracy of 80% when identifying the PID problem with the mathematical neural network model and are obtained within a 2 h testing time. From the above results, these methods succeed in reducing cost of materials and testing time during the manufacturing process; thus, this study has an industrial application value. Concurrently, Method-3 and Method-4 are rarely seen in the limited literature review for identifying PID problem; therefore, this study also offers a novel contribution for technical application innovation.

Supercharging cell-level potential-induced degradation (PID) testing using a salt-enriched hybrid polymer layer

Potential-induced degradation of the shunting type (PID-s) is a well-known problem for photovoltaic modules. However, standard PID testing at the cell or module level takes 96 h due to the time it takes for the Na ions to diffuse from the glass to the solar cell through the ethylene-vinyl acetate (EVA) encapsulant. This is too slow to monitor production quality in the fast-paced solar cell industry. Moreover, it results in the encapsulation of solar cells, significantly restricting characterization options after PID testing. In this work, we replace the EVA in the PID testing setup with a salt-enriched hybrid polymer, which provides the solar cell with direct access to sodium (Na) ions while at the same time avoiding encapsulation during the testing process. Solar cells that underwent PID-s testing with the salt-enriched hybrid polymer showed a maximum degradation after only 12 min, over two orders of magnitude faster than standard PID-s testing using EVA, which took 4,300 min (∼72 h) to reach maximum degradation. Hence, PID-s testing using the salt-enriched hybrid is significantly faster than conventional techniques and avoids encapsulation, thus allowing for more detailed post-PID cell analysis. This new test shows that some solar cells can recover from PID-s, which was corroborated by extending the standard test to 300 h. This important novel insight shines a new light on the PID-s mechanism and the impact of this failure mode in field operation.

Tolerance to hygrothermal and high-voltage stresses for Si-related photovoltaic modules with newly-developed polyvinyl butyral encapsulants

Newly-developed polyvinyl butyral (PVB) encapsulants were employed for Si-related photovoltaic modules. Modules of amorphous Si with a glass–glass structure and those of crystalline Si with glass and a back-sheet structure were subjected to hygrothermal stresses by a damp-heat (DH) test and high-voltage stress by a potential-induced degradation (PID) test, respectively. Even after a quite long DH test at 85 °C and 85% relative humidity for 49 000 h, retention of output power of about 85% was obtained without edge sealant. No decrease in output power was also observed after a PID test with −1000 V at 60 °C and 85% relative humidity for 168 h. These facts suggest that newly-developed PVB is well applicable to encapsulant materials for highly reliable photovoltaic modules.

Review of Potential‐Induced Degradation in Bifacial Photovoltaic Modules

Bifacial modules are increasingly deployed in the field and are expected to represent half of the market share within 10 years. Their rear structure differs from monofacial modules to allow additional light absorption. However, it brings new reliability challenges to address. In particular, the risk of potential‐induced degradation (PID) is increased as both module sides are impacted. Different PID processes have been identified in the literature: shunting type (PID‐s), polarization type (PID‐p), Na penetration type, and corrosion type (PID‐c). Their occurrence depends on the photovoltaic system configuration as well as the module's materials. Apart from PID‐s, PID processes are not well understood and extensive research is needed to elucidate the PID scenario and underlying mechanisms. Herein, current knowledge about PID processes and their impact on the main bifacial modules in the market are gathered with the aim to guide future research. Bifacial module technologies and leakage current paths leading to PID are described. Indoor and outdoor PID testing methods are detailed. For each bifacial module technology, the PID processes are investigated with their indicators, mechanism and recovery process. PID‐impacting factors and limitation solutions are finally reported and a state of the art on PID modeling is presented.

Potential-induced degradation of n-type front-emitter crystalline silicon photovoltaic modules — Comparison between indoor and outdoor test results

We perform indoor and outdoor potential-induced degradation (PID) tests for n-type front-emitter (n-FE) crystalline Si (c-Si) photovoltaic (PV) modules and compare their results. The indoor/outdoor acceleration factor for the polarization-type PID (PID-p) of n-FE PV modules is found to be ∼1000 at an indoor test temperature of 85 °C. We observe the progression of the PID-p of n-FE PV modules in rainy days, while their performance is recovered in sunny days. This may be because of the formation of a water film on a module surface acting as a conductive film, resulting in a larger electric field near the n-FE cells in rainy days. The recovery of the PV performance of n-FE modules in sunny days can partly explain the large acceleration factor for the indoor PID test against the outdoor test. • We performed indoor and outdoor PID tests for n-FE PV modules. • n-FE PV modules show polarization-type PID (PID-p) both indoors and outdoors. • The acceleration factor for the PID-p is ∼1000 at an indoor test temperature of 85 °C. • We observe the recovery of PID-p for the outdoor modules in sunny days. • The recovery may be one of the reasons for the large acceleration factor.

Development of a Suppression Technique of Potential-Induced Degradation by a Formation of Glass Layer in Si PV Modules

Shunt-type potential-induced degradation (PID) is one of the degradation phenomena of photovoltaic (PV) modules which degrade PV performance drastically in short time compared to other degradation modes. In this paper, a new suppression technique of the PID was developed by coating a glass layer (GL) on the top or bottom surface of cover glass using a chemical solution known as liquid glass. PID tests were conducted using PV modules prepared with and without GL. A clear suppression effects of the PID were observed by forming GL, and the occurrence of the PID was delayed about 4 times by the formation of GL on the bottom side of cover glass in PV modules.

Evaluation of bifacial module technologies with combined‐accelerated stress testing

AbstractIn view of the increasing interest and market share of bifacial cells and modules, suitable substrates such as glass and transparent backsheets along with ethylene vinyl acetate (EVA) and polyolefin elastomer (POE) encapsulants were examined in combined‐accelerated stress testing (C‐AST) to evaluate and compare degradation modes. Testing with both monofacial and bifacial cells, we found that glass–glass modules with monofacial cells led to greater grid finger breakage than those with polymeric backsheets. This is attributed to previous X‐ray topography and modeling work showing higher stress in cells and interconnections in glass–glass modules than glass backsheet modules. Consistent with the objectives of C‐AST, which stresses modules at levels corresponding to the limits seen in the natural environment, we observed the UV‐fluorescence signatures of modules tested in C‐AST (considering the degradation associated with developing chromophores, moisture penetration, and photobleaching effects) to be like those in fielded modules, more so than other chamber stress testing implemented for comparison. We found light‐induced degradation (LID) in module types with regenerated (inactive) cells with C‐AST, suggesting the possibility of LID destabilization in some field conditions. We could also distinguish potential‐induced degradation (PID) on the back of the bifacial passivated emitter and rear cells (PERC) in C‐AST. Confirming with ex situ tests, we found polarization‐type PID most prevalent in glass‐glass modules with EVA as would be anticipated considering the greater leakage current through such module encapsulation. Unlike PID tests performed in the dark, which can lead to false positive PID test results, field‐representative illumination is experienced by the modules on the front and back sides while −1200 V system voltage is applied in C‐AST, supporting the conclusion that this module type with glass‐glass construction would be susceptible to PID in the field.

Potential-induced degradation in perovskite/silicon tandem photovoltaic modules

Despite great progress in perovskite/silicon tandem solar cells’ device performance, their susceptibility to potential-induced degradation (PID) remains unexplored. In this study, we find that applying a voltage bias of −1,000 V to single-device perovskite/silicon tandem modules at 60°C for ∼1 day can cause a ∼50% loss in their power conversion efficiency, which raises concerns for tandem commercialization. We found no accumulation of Na+ in the perovskite or silicon photon absorbers. Consequently, no obvious shunt is observed in our silicon subcells. We also find that elements diffuse from the perovskite into the module encapsulant during PID testing. We argue that this diffusion is the main PID mechanism in our tandem modules. While applying a large positive voltage bias can partially recover this PID, introducing barriers or structures to prevent elemental diffusion out of the perovskite may be required to mitigate this degradation phenomenon.

Rapid testing on the effect of cracks on solar cells output power performance and thermal operation

This work investigates the impact of cracks and fractural defects in solar cells and their cause for output power losses and the development of hotspots. First, an electroluminescence (EL) imaging setup was utilized to test ten solar cells samples with differing crack sizes, varying from 1 to 58%. Our results confirm that minor cracks have no considerable effect upon solar cell output, and they develop no hotspots. However, larger cracks can lead to drastic decreases in the output power, close to − 60%. Furthermore, as the crack area increased, there was a further increase in the cell's temperature under standard test conditions. On the contrary, no hotspots were found for the solar cells affected by significant creak areas (crack percentage > 46%) because there were insufficient areas to develop a hotspot. Last, a comparative analysis with solar cells affected by potential induced degradation (PID) was made. We found a strong relationship in the output power losses, and the PID test critically impacted the cells by developing localized hotspots at a temperature level close to 50 °C.

Recovery of potential-induced degraded p-type multicrystalline Si PV modules by application of a reverse DC bias

Potential-induced degradation (PID) of photovoltaic (PV) modules based on p-type crystalline Si occurs in large-scale PV systems. The development of a low-cost PID recovery technique is important to maximize the power generation capacity of PID-affected facilities. In this paper, we study a simple PID recovery method for multicrystalline silicon solar cells. PID recovery was conducted by application of a reverse DC-bias voltage to the p-n junction of solar cells in PV modules, without temperature control devices. By using this method, the conversion efficiency of solar cells reduced to approximately 20% of their initial value via a PID test was recovered up to 92%. Additionally, nonuniform temperature increases of PV modules by leakage current were observed during the voltage application.

Experimental investigation of potential induced degradation of poly-crystalline photovoltaic modules: Influence of superstrate and encapsulant types

Potential induced degradation (PID) is amongst the most critical degradation phenomena affecting reliability of PV modules by causing power losses. In this research, PID was induced on PV modules in an environmental chamber in accelerated temperature and humidity conditions under the application of high voltage stress. The primary focus of this paper was to quantify the degradation extent of PV modules with different encapsulant and superstrate/glass types. The encapsulant types investigated were EVA and newly developed PVB. The superstrate types investigated were Soda-lime and Quartz. The progression and severity of degradation were determined through I-V measurements and EL imaging, revealing losses in Pmax and FF. The leakage current was measured during the PID test and no correlation between leakage current and power was observed. It was demonstrated that the PID loss was strongly dependent on the electrical and physical properties of the superstrate and encapsulant types. The module with quartz/EVA configuration experienced lower (17%) PID losses compared to the soda-lime/EVA module (32%). Similarly, the module with soda-lime/PVB configuration experienced lower (10%) PID losses compared to the soda-lime/EVA module (32%). While the module having both the quartz and PVB, exhibited the lowest PID progression with only 1% degradation in power.

Effect of temperature and pre-annealing on the potential-induced degradation of silicon heterojunction photovoltaic modules

We investigate the effect of temperature and pre-annealing on the potential-induced degradation (PID) of silicon heterojunction (SHJ) photovoltaic (PV) modules. SHJ PV modules show a faster decrease in short-circuit current density (J sc) at higher temperatures during PID tests. We also observe a complex relationship between the degree of the J sc decrease and temperature during the PID tests. Pre-annealing before the PID tests at sufficiently high temperatures leads to the complete suppression of the PID of SHJ PV modules. The decrease in J sc is known to be due to the chemical reduction of indium (In) in transparent conductive oxide (TCO) films in SHJ cells, in which water (H2O) in SHJ modules is involved. These indicate that H2O may out-diffuse from the SHJ PV modules during a PID test or pre-annealing at sufficiently high temperatures, by which the chemical reduction of indium in TCO to metallic In is suppressed.

Reduction of Potential-Induced-Degradation of p-Type PERC Solar Cell Modules by an Ion-Diffusion Barrier Layer Underneath the Front Glass

With the maturation of silicon-based technologies, silicon solar cells have achieved a high conversion efficiency that approaches the theoretical limit. Currently, great efforts are being made to enhance the reliability of silicon solar cells. When the silicon solar cells are made into modules, potential-induced-degradation (PID) occurs during operation because of the high voltage applied between the frame and the cells, which reduces the efficiency and output power. The diffusion of Na+ ions from the front glass and the increased leakage current along the migration path are the major causes of PID. In this work, atomic layer deposition (ALD)-grown amorphous thin Al2O3 layers are introduced underneath the front glass to prevent the diffusion of Na+ ions and the resulting PID. Accelerated PID tests showed that an ALD-grown Al2O3 layer of 30 nm could effectively suppress PID seriously affecting the conversion efficiency or light transmittance. The introduction of an ion-diffusion barrier underneath the front glass is expected to contribute to securing the long-term reliability of silicon-based electricity generation, together with the introduction of barrier layers inside the solar cells.

Post‐mortem analysis of a commercial Copper Indium Gallium Diselenide (CIGS) photovoltaic module after potential induced degradation

AbstractAn extensive post‐mortem analysis was conducted on a commercial copper‐(indium‐gallium)‐diselenide (CIGS) photovoltaic module that degraded after exposure to the high voltage stress of a standardized potential induced degradation (PID) test. We employed a custom‐developed coring technique to extract samples from the full‐size field module, which showed degraded and nondegraded areas (regarded as reference) in electroluminescence after the PID test. The resulting solar cell samples were compared based on their electrical properties and sodium profiles using a wide range of laboratory‐based analysis techniques including photoluminescence and lock‐in thermography imaging, current–voltage measurements, and glow discharge optical emission spectroscopy. The samples that were extracted from the degraded areas of the module showed lower photoluminescence intensity and had significantly lower open‐circuit voltage V(oc) and fill factor (FF) values in comparison with reference samples. An increased content of sodium within the absorber layer was also observed for these samples, linking sodium migration to PID. These observations at the module level are consistent with earlier reports on PID‐stressed CIGS cells and mini‐modules. This is to our knowledge the first reported study of a microscopic investigation on a real‐life full‐scale CIGS module after PID.

Influence of light irradiation on the charge-accumulation-type potential-induced degradation of n-type front-emitter crystalline Si photovoltaic modules

We investigated the influence of light irradiation on the charge-accumulation-type potential-induced degradation (PID) of n-type front-emitter (n-FE) crystalline silicon (c-Si) photovoltaic (PV) modules. A PID test under one-sun irradiation leads to faster reductions of short-circuit current–density (J sc) and open-circuit voltage (V oc) compared to the case of a PID test in the dark. This indicates that light irradiation accelerates the charge-accumulation-type PID of the n-FE PV modules. The J sc and V oc reductions become slower under irradiation without ultraviolet (UV) light, showing almost the same time dependence as the PID test in the dark. The acceleration of PID by the addition of UV light may be explained by the excitation of electrons at K0 centers in silicon nitride (SiN x ) and their faster drift to the surface by the electric field applied to SiN x .

Metal-doped titanium oxide films for suppressing potential-induced degradation of photovoltaic modules

Titanium oxide films were prepared from peroxotitanium complex aqueous solution containing a peroxo complex of vanadium, molybdenum or tungsten of 2, 5, 10 mol % by heating at 200 °C for the purpose of suppressing the photocatalytic activities that may be developed by crystallization during long-term use as a prevention film against potential-induced degradation (PID) of crystalline silicon (c-Si) photovoltaic (PV) module. The films containing those dopants crystallized to anatase by hydrothermal treatment at 100 °C for 15 h as an acceleration test, but hardly showed any photocatalytic activity. According to the lattice constants, X-ray photoelectron spectroscopy analyses and UV–visible light reflection spectra, it was estimated that vanadium (V), molybdenum (VI) and tungsten (VI) were substituted with titanium (IV) in titanium oxide heated at low temperature of 200 °C. The titanium oxide films containing the dopants of 2 mol % were coated at 200 °C onto the rear side of front cover glass with 200 nm thickness. No significant PID was observed in the c-Si PV modules based on the film-coated glass by a PID test by applying −1000 V at 85 °C for 2 h.

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.

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.