Glass Encapsulation Research Articles

다양한 환경조건에서 태양전지모듈의 PID회복특성

The Potential Induced Degradation(PID) in PV module mainly affected by various performance conditions such as a potential difference between solar cell and frame, ambient temperature and relative humidity. The positive charges as sodium ions in front glass reach solar cell in module by a potential difference and are accumulated in the solar cell. The ions accelerate the recombination of generation electrons within solar cell under illumination, which reduces the entire output of module. Recently, it was generally known that PID generation is suppressed by controlling the thickness of SiNx AR coating layer on solar cell or using Sodium-free glass and high resistivity encapsulant. However, recovery effects for module with PID are required, because those methods permanently prevent generating PID of module. PID recovery method that voltage reversely applies between solar cell and frame contract to PID generation begins to receive attention. In this paper, PID recovery tests by using voltage under various outdoor conditions as humidity, temperature, voltage are conducted to effectively mitigate PID in module. We confirm that this recovery method perfectly eliminates PID of solar cell according to repeative PID generation and recovery as well as the applied voltage of three factors mainly affect PID recovery.

On the Performance Degradation of Poly(3-Hexylthiophene) Field-Effect Transistors

Polymeric transistor degradation was investigated on bottom and top gate structures. Shelf-lifetime studies in both kinds of devices demonstrate an accelerated increase in effective charge carrier mobility, threshold voltage, and off current in modulus when poly(3-hexylthiophene) (P3HT) is exposed to atmospheric gases. Although P3HT is underneath PMMA dielectric and gold gate electrode films, electrical parameters degradation can be only delayed by 100 h. Therefore, only glass encapsulation of the active area is capable of effectively preventing current modulation decrease after exposure to atmospheric gases. Differently from their bottom-gate counterparts, capped top-gate TFTs clearly present negative threshold voltage and positive hysteresis. An interface with reduced deep traps concentration and electrical characterization influence on shallow traps filling are believed to play a significant role in these top-gate P3HT/PMMA transistors under operating conditions. Alternating gate voltage stress along 3000 cycles provides evidence of electrical sweep as a cause of performance degradation. Similarly, dc gate bias stress monitored for 127 min can impair current modulation and shifts threshold voltage depending on its sign. Finally, reversibility of both kinds of stress points that shallow traps are the major problem in these capped devices.

Vitrification of β-tricalcium phosphate in sodium aluminoborophosphate glass and the effect of Ga3+ substitution

Sodium calcium aluminoborophosphate glasses (some containing Ga3+) simulate interactions at the interface between β-tricalcium phosphate crystal waste hosts (β-TCP and β-TC(Ga)P) and sodium aluminoborophosphate (NABP) glass encapsulant. 31P NMR and Raman spectroscopies show progression from Na+ charge-balanced, mixed QAlP=Q21+Q30 in the NABP base glass, to Ca2+ charge-balanced, Q00 dominated structure, eventually inhibiting vitrification above 80wt% addition of β-TCP or β-TC(Ga)P. 27Al NMR shows [Al(PO4)n] species with dominant n=4 and 11B NMR shows the 4-coordinated boron fraction in NABP falls from 0.7 to 0.1 on addition of the crystal hosts. Devitrification of glasses with 60–70wt% crystal additions shows that Na+ and Al3+ from the encapsulant substitute for ∼20% of Ca2+ in the β-TCP phase formed from the β-TCP:NABP glasses whilst ∼85% of Ga3+ resubstitutes into β-TCP from the β-TC(Ga)P:NABP glasses. This demonstrates the preference for Ga3+ substitution over Al3+ in the Ca(5) site.

Material and technological aspects of high-temperature SiC device packages reliability

Purpose – The purpose of this paper is to deal with material and technological aspects of SiC diodes assembly in ceramic packages. The usefulness of combinations of different materials and assembly techniques for the creation of inner connection system in the ceramic package, as well as the formation of outer connections able to work at temperatures up to 350°C, were evaluated. Design/methodology/approach – The ceramic package consists of direct bonded copper (DBC) substrate with Cu pads electroplated by Ni or Ni/Au layers on which a SiC diode was assembled by sintering process using Ag microparticles. For the connections inside the ceramic package, the authors used Al/Ni and Au-Au material system based on aluminium or gold wire bonding. The authors sealed the ceramic package with glass encapsulation and achieved a full encapsulation. Outer connections were manufactured using Cu ribbon plated with Ag layer and sintered to DBC by Ag micro particle. The authors investigated the long-term stability of electrical parameters of SiC diodes assembled in ceramic package at temperature 350°C. Findings – The authors have shown that Schottky and PiN SiC diodes assembled with different technologies and materials in ceramic package keep their I-V characteristics unchanged during ageing at 350°C for 400 h. Originality/value – The SiC diodes assembled into ceramic package with Al/Ni or Au-Au inner electrical connection systems and outer connections system based on Ag microparticles sintering process of Cu/Ag ribbon to DBC substrate can work reliably in temperature range up to 350°C.

Sodium Decoration of PID-s Crystal Defects after Corona Induced Degradation of Bare Silicon Solar Cells

It is proven that potential-induced degradation leading to shunting of crystalline silicon solar cells (PID-s) is caused by stacking fault-like planar crystal defects penetrating the p-n junction that become decorated with sodium due to high electric fields across the dielectric antireflective coating (ARC). Often it is assumed that sodium found in PID-s affected cells originates from the cover glass used for photovoltaic modules. In this contribution, we show that PID-s also occurs at bare silicon solar cells without polymer foil or glass encapsulation. Using corona discharge induced degradation, it is shown that sodium decorated, shuntingcrystal defectsare generated. This sodium likely originates from contaminations present on the solar cell surface. Therefore, it is concluded that PID-s of solar modules also mainlyarises from sodium contaminationsof the solar cell surfaceand not from the glass. Whether PID-s occurs or not depends on the electric field across the ARC, influenced by theelectrical resistance of polymer foil and glass. So called sodium-free glass results in a low electric field due to the high resistance of the glass.

Reliability of a printed Cu busbar electrode on a conventional silicon solar cell

In this paper, we describe the reliability of the Cu busbar electrode fabricated by screen printing of resin-based Cu pastes on a crystal silicon solar cell with conventional front and rear electrodes excluding the busbar. The damp heat test (DHT) and thermal cycling test (TCT) of the cells were carried out with ethylene-vinyl acetate (EVA) and glass encapsulation, and without any encapsulation. No significant degradation was observed for either case. Oxidation was confined to the surface region even without encapsulation after 2,500 h of DHT. Cu diffusion into Si was evaluated using pseudo fill factor (pFF). No significant changes in pFF were found after heat treatment (400 °C, 1 h) in the case of resin-based Cu, where 10% pFF loss was observed when Cu was introduced by vapor deposition. From these findings, the role of resin used as a binder in Cu pastes is considered a key material parameter of Cu diffusion in Si.

Drift characteristics of mobile ions in SiNx films and solar cells

Low temperature (30–200°C) drift characteristics of mobile ions in PECVD SiNx films and solar cells were determined for the first time using a non-contact ion-drift spectrometry technique adopted from silicon integrated circuit (IC) metrology. The results demonstrate drift of Na+ ions in PECVD SiNx films that begin at temperatures as low as 50°C. This is a seemingly contrasting behavior as compared to SiNx films used in microelectronics where it provides excellent protection as a diffusion barrier. The present study was carried out on SiNx films and final solar cells intentionally contaminated with Na, K, and Cu. In non-contact ion-drift spectrometry an electric field across the dielectric is created by charge deposited on the dielectric surface with a corona discharge in air. Temperature stress is applied by ramping the temperature with time at a controlled rate. Ion drift decreases the dielectric voltage that is monitored with a vibrating Kelvin-probe. Voltage versus time, voltage versus temperature, and corresponding derivative characteristics are used to quantify drift velocity, ion concentration and drift activation energy. The latter produces characteristic ion peaks in the derivative spectra dV/dT versus temperature. The metrology version for mobile ion mapping is based on whole-wafer corona bias-temperature stress at selected temperatures corresponding to drift of different ions. The mapping is a powerful means for ion source identification, such as Na from cell encapsulation glass. It shall prove advantageous for further clarification of the role of Na in potential induced degradation (PID) effects i.e. the polarization effect and the potential induced shunting (PIS).

Flexible Lamination Encapsulation.

A novel flexible encapsulation method (Flex Lami-capsulation) is reported, which can be applied in the roll-to-roll process for mass production of organic electronic devices. Flex Lami-capsulation is very simple, fast, and getter-free, and is as effective as glass encapsulation. Use of this method is feasible in large-area flexible displays and does not have the drawbacks of conventional encapsulation methods.

Single-Step Soft-Imprinted Large-Area Nanopatterned Antireflection Coating.

We demonstrate an effective nanopatterned antireflection coating on glass that is based on sol-gel chemistry and large-area substrate-conformal soft-imprint technology. The printed 120 nm tall silica nanocylinders with a diameter of 245 nm in a square array with 325 nm pitch form an effective-index (n = 1.20) antireflection coating that reduces the double-sided reflection from a borosilicate glass slide from 7.35% to 0.57% (averaged over the visible spectral range) with a minimum reflectance <0.05% at 590 nm. The nanoglass coating is made using a simple process involving only spin-coating and an imprint step, without vacuum technology or annealing required. The refractive index of the nanoglass layers can be tailored over a broad range by controlling the geometry (1.002 < n < 1.44 in theory), covering a wide range that is not achievable with natural materials. We demonstrate that the nanoglass coating effectively eliminates glare from smart-phone display windows and significantly improves the efficiency of glass-encapsulated solar cells. These features, that are achieved over an angular range as wide as ±50°, together with strong hydrophobicity and mechanical durability, make nanoglass coatings a promising technology to improve the functionality of optoelectronic devices based on glass encapsulation.

Conductive cooling in white organic light emitting diode for enhanced efficiency and life time

We demonstrate white organic light emitting diodes with enhanced efficiency (26.8 lm/W) and life time (∼11 000 h) by improved heat dissipation through encapsulation composed of a metal (Cu, Mo, and Al) and mica sheet joined using thermally conducting epoxy. Finite element simulation is used to find effectiveness of these encapsulations for heat transfer. Device temperature is reduced by about 50% with the encapsulation. This, consequently, has improved efficiency and life time by about 30% and 60%, respectively, with respect to glass encapsulation. Conductive cooling of device is suggested as the possible cause for this enhancement.

Effect of Glass Refractive Index on Light Extraction Efficiency of Light‐Emitting Diodes

Light‐emitting‐diode (LED) encapsulants, such as epoxy and silicone resin, have a lower refractive index than YAG:Ce phosphor, and this is usually one of the major causes of LED inefficiency. To improve LED performance, a glass encapsulant is considered. In this study, the SiO2–B2O3–ZnO glass system containing La2O3 and WO3 was investigated as an encapsulant to minimize total internal reflection and to increase the light extraction efficiency of LED packages. The characterization of glass encapsulants was performed using a differential scanning calorimeter, a pycnometer, a prism coupler, X‐ray photoelectron spectroscopy, and integrating spheres. The refractive index increased linearly with increasing molar volume of glass because La2O3 and WO3 act as modifiers in the glass, creating more nonbridging oxygen. The refractive index of glass increases with the content of La2O3 and WO3, which is attributed to the increase in polarizability of oxide ions in the glass. When the refractive index between glass and phosphor matched, light extraction efficiency was maximized because total internal reflection decreased.

Thermal-Stability Comparison of Glass- and Silicone-Based High-Power Phosphor-Converted White-Light-Emitting Diodes Under Thermal Aging

The lumen degradation, chromaticity shift, transmittance loss, and mean-time-to-failure (MTTF) evaluation in glass- and silicone-based high-power phosphor-converted white-light-emitting diodes (LEDs) (PC-WLEDs) under accelerated thermal aging at 150 °C, 200 °C, and 250 °C are presented and compared. The silicone-based PC-WLEDs exhibited less thermal stability than the glass-based PC-WLEDs by 1.86, 2.79, and 4.76 times higher lumen losses, 3.05, 3.26, and 6.84 times larger chromaticity shifts, and 1.82, 2.62, and 6.67 times greater transmittance losses at 150 °C, 200 °C, and 250 °C, respectively. The results also showed that the glass-based PC-WLEDs exhibited higher MTTF than the silicone-based PC-WLEDs by 20 times at room temperature. The peaks of the emission and excitation spectra for both silicone and glass phosphors were not significantly changed after thermal aging, evidenced by fluorescence spectrophotometer analyses. This indicated that the fluorescent ability of Ce:YAG-doped phosphor materials did not change after thermal aging and the transmittance loss was corresponding to the lumen loss and chromaticity shift. The results of the lumen loss, chromaticity shift, transmittance loss, and MTTF investigations clearly demonstrated that the thermal-stability performance of the glass-based PC-WLEDs was better than that of the silicone-based PC-WLEDs. The advantage of employing doped glass encapsulation in high-power PC-WLEDs could be explained: The material property of glass transition temperature of 750 °C was higher than that of silicone transition temperature of 150 °C. A better thermal stability phosphor layer of glass as encapsulation material may be beneficial to many applications where the LED modules with high power and high reliability are demanded for use in next-generation solid-state lighting.

Combined effect of light harvesting strings, anti-reflective coating, thin glass, and high ultraviolet transmission encapsulant to reduce optical losses in solar modules

Optical losses are a major source for current and power reduction in solar modules. Hence, various improvements aiming at reducing these losses have been suggested. In this work, we have evaluated the effects of anti-reflective coating, front glass thickness, polyvinyl butyral ultraviolet+ encapsulant, and light harvesting strings on the module performance individually and in combination. The individual and combined contributions were quantified by spectrally resolved optical measurements on the module components and simulations as well as electrical measurements on 1-cell and 54-cell modules. Optical gains and their impact on short circuit current are discussed in relation to a maximum current obtained from the solar cells internal quantum efficiency. The results of the electrical characterization are in good agreement with the optical analysis substantiating our approach. They show that a combined, relative current enhancement of 5% can be obtained for an optimized module, which compares to an increase of 1% absolute efficiency. Copyright © 2014 John Wiley & Sons, Ltd.

Technologies d'encapsulation avancées pour l'électronique organique

Organic electronics has emerged in the 1980's and is today a well-developed discipline in the scientific world. Among the most common devices, Organic Light Emitting Diodes (OLEDs) and Organic PhotoVoltaic cells (OPV) have been widely studied : the OLED technology is already marketed today as OLED-based displays that can be found in modern smartphones. The problem with these circuits and organic semiconductors in general lies in their rapid degradation in case of contact with oxidizing gases of the atmosphere, water and oxygen. Therefore, efficient encapsulation processes are needed to achieve sufficient reliability and lifetime. Up to now, complex and expensive glass encapsulation methods have been used. To circumvent these issues, new encapsulation processes have been developed to achieve reliable, low cost, flexible, conformable and less brittle organic-based products.

Elucidation on Joule heating and its consequences on the performance of organic light emitting diodes

Current work presents a quantitative analysis of Joule heating by temperature measurements using infrared thermography and heat estimation of organic light emitting diodes (OLEDs) and their correlation with device life time. These temperature measurements were performed at 10, 20, 30, 40, and 50 mA/cm2 current densities and studied with operational time. The temperature rise of the device has increased from 9.8 to 16.6 °C within 168 h at an operating current density of 40 mA/cm2. This has been ascribed as due to the external contamination by water, oxygen, and dust particles as well as by internal heat generation. Encapsulation of the device avoids external degradation of OLEDs by preventing the destruction caused by these external contaminations. In this way, encapsulation has led to the decreased temperature rise of 12.4 °C within the duration of 168 h, which reflects the improved stability of the device. The temperature measured has been used to calculate the heat generated inside the device by solving the heat conduction equation using a transverse matrix approach. It has been found by these calculations that about 97%–98% of the power supplied to the device are converted into the heat for un-encapsulated device and results in rapid degradation of device with time, which in turns leads to the increase in operating voltage and decrease in luminous intensity with operational time. Proper encapsulation has reduced the heat generated inside the device by about 3%–4%, thereby, increasing the life time of the device. However, the glass encapsulation reduces the possibilities of the device cooling by heat convection to the atmosphere and prohibited the maximum utilization of encapsulation.

Top-emission organic light emitting diodes with lower viewing angle dependence

We obtained nanoporous polymer film which has 20–30% optical haze to suppress the viewing angle dependency of a top emission organic light emitting diode (TOLED) with strong microcavity effect. We controlled the sizes and density of nanopores by changing the spin coating condition such as spinning duration and spin rate in highly humid atmosphere up to 90% relative humidity condition. The resultant nanoporous polymer film has effectively reduced viewing angle dependency of microcavity TOLEDs without any serious decrease in total intensity of out-coupled light observed from the integrating sphere although the luminance observed from the front side was diminished slightly. Despite its negative effect on the efficiency toward the front direction, we could use those nanoporous polymer films as scattering media or diffuser layer on top of the encapsulation glass because it could change the strongly directed emission toward desired emission with Lambertian distribution.

Improvement of light out-coupling efficiency in organic light-emitting diodes with variable nanopatterns

We present a viable method to enhance the current efficiency of organic light-emitting diodes (OLEDs) by imprinting cylindrical nanopatterns (NPs) onto a glass substrate. Herein, OLEDs equipped with an optimum NP array having a diameter of 300 nm and a periodic distance of 500 nm show a 33.4% improvement in current efficiency compared with a device without NPs. The light extraction efficiency of OLEDs was enhanced using a nanopatterned glass substrate, without any electrical degradation owing to the formation of NPs on opposite sides of the organic layers. In addition, top-emitting OLEDs can be fabricated easily by patterning the encapsulation glass.

Advanced microhole arrays for light trapping in thin film silicon solar cells

We present a comprehensive theoretical analysis accompanying our experimental development of micro-structured thin film polycrystalline silicon solar cell absorbers. Our focus is on 2D-periodic arrays of holes which do not act as a superficial scattering grating but pierce the entire silicon absorber layer. We deviate from the commonly used model of vertical hole sidewalls by employing conical frustum shaped holes with a range of opening angles. Additionally, an experimentally motivated front texture is applied to the simulated solar cell absorbers and varied in texture aspect. Based on this parametric absorber model, for a single domain period of 2μm, we discuss light trapping and optical losses in thin film cells with absorptive front and back contacts and a perfectly transparent glass encapsulation layer. Implications from this study are that light trapping in square periodic arrays with periods larger than the wavelength of light can be enhanced by microholes but that it cannot replace a front texture which provides both antireflection and scattering.

The effects of auxiliary electric field within the electrohydrodynamic atomization encapsulation chamber on particle size, morphology and collection efficiency

Electrohydrodynamic atomization (EHDA) or electrospray has been lately applied to fabricate drug carriers in the dosage forms of polymeric micro- and nano-fibers and particles. In the current study, EHDA process was performed in a glass encapsulation chamber to facilitate the formation of solid pharmaceutical particles after solvent evaporation from the electrosprayed droplets. High voltage nozzle and ring are enclosed in the named EHDA encapsulation chamber together with a grounded collecting plate. The unique feature of the design was an additional aluminum plate located a few centimeters above the collecting plate which was positively charged using a high voltage supplier. Furthermore, a simple finite-element model was generated to investigate the efficacies of flow and electric fields. This work aimed to investigate the effect of the auxiliary electric field on particle collection efficiency, morphology and size distribution. The final results show that application of the auxiliary electric field can clearly enhance particle collection efficiency in comparison to the EHDA process without auxiliary electric field. Additionally, it was established that the particle size distribution was not considerably influenced by the auxiliary electric field. On the contrary, the smoothness of the particles can be affected by the auxiliary electric field especially when a high voltage is applied to the flat plate.

OLED 소자 제조를 위한 주울 가열 봉지 공정 시 도전층 구조에 따르는 열분포

Encapsulation is required since organic materials used in OLED devices are fragile to water vapor and oxygen. Laser sealing method is currently used where IR laser is scanned along the glass-frit coated lines. Laser method is, however, not suitable to encapsulating large-sized glass substrate due to the nature of sequential scanning. In this work we propose a new method of encapsulation using Joule heating. Conductive layer is patterned along the sealing lines on which the glass frit is screen printed and sintered. Electric field is then applied to the conductive layer resulting in bonding both the panel glass and the encapsulation glass by melting glass-frit. In order to obtain uniform bonding the temperature of a conductive layer having a shape of closed loop should be uniform. In this work we conducted simulation for heat distribution according to the structure of a conductive layer used as a Joule-heat source. Uniform temperature was obtained with an error of 5% by optimizing the structure of a conductive layer. Based on the results of thermal simulations we concluded that Joule-heating induced encapsulation would be a good candidate for encapsulation method especially for large area glass substrate.