Thermal expansion behavior of solar cell encapsulation materials

Knausz, Marlene; Berger, Karl; Voronko, Yuliya; Eder, Gabriele; Koch, Thomas; Pinter, Gerald

doi:10.1016/j.polymertesting.2015.04.009

Cited by 29 publications

(9 citation statements)

References 9 publications

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“…Moreover, the different thermal expansion behaviors of the components of a PV module are well known to generally result in internal stresses because the coefficient of thermal expansion of the EVA is much larger than that of Si (the coefficients of thermal expansion of EVA and Si were 2.70 × 10 −4 and 2.49 × 10 −6 , respectively) . Therefore, these large stresses caused by the EVA deformation may result in cracked solar cells and might have caused the formation of the diagonal cracks that preferentially occurred on the crystallographic planes, where the material toughness was lower . In this regard, Kang et al reported that the cracks caused by stress in a c‐Si wafer can relatively easily initiate and propagate along the <100> direction because this direction corresponds to that of the lowest plane strain tensile modulus.…”

Section: Resultsmentioning

confidence: 99%

Simple pretreatment processes for successful reclamation and remanufacturing of crystalline silicon solar cells

Lee

Ahn

et al. 2017

Progress in Photovoltaics

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This study presents an effective method for recovering unbroken solar cells from photovoltaic (PV) modules. The combustion process is effective at removing ethylene vinyl acetate (EVA) in PV modules. However, the solar cell tends to break during the combustion process. We verify that the breakage mechanisms of the solar cell in the module are related to the thermal changes of EVA during the heat treatment process, that is, generated gases form bubbles behind the glass, and the thermal deformation of the rear EVA applies stress to the solar cell. This study investigates the simple pretreatments of glass cracking and EVA patterning to prevent the breakage behavior. An unbroken solar cell was successfully recovered from the module after complete EVA removal using the combustion process. The recovered solar cell was immersed in a mixed acid solution of HNO 3 and HF to reclaim the crystalline silicon wafer, which subsequently underwent the solar cell manufacturing process. The PV performances of the solar cells based on the reclaimed wafer and a commercial wafer were evaluated and compared. The PV performance of the solar cell manufactured from the reclaimed wafer was measured at 18.5%, whereas that from the commercial wafer-based solar cell was measured at 18.7%. Consequently, the considered pretreatment processes yielded solar cells acceptable for use in the PV industry.

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Section: Resultsmentioning

confidence: 99%

Simple pretreatment processes for successful reclamation and remanufacturing of crystalline silicon solar cells

Lee

Ahn

et al. 2017

Progress in Photovoltaics

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“…As a brittle material, silicon solar cells fail under the tensile stress; therefore, compressive stress is not crucial for solar cells. However, independently of the direction, high stresses can lead to delamination [23] and interconnector fatigue [24]. When exposed to ML, the dominating stress in the solar cells is tensile.…”

Section: Methodsmentioning

confidence: 99%

The Effect of Cell and Module Dimensions on Thermomechanical Stress in PV Modules

Beinert

Romer

Heinrich

et al. 2020

IEEE J. Photovoltaics

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We present an evaluation of the silicon solar cell as well as the photovoltaic (PV) module size and its effect on thermomechanical stress. The evaluation is based on finite-element method (FEM) simulations. Within these simulations, we perform parameter variations of the number of solar cells within a PV module from 60-140 cells, of the cell size from 156.0-161.75 mm, and the cell format from full cells down to quarter cells. The FEM simulations cover the lamination process, mechanical load, and thermal cycling for glass-foil as well as glass-glass modules. The presented results reveal correlations between the solar cell and module size with the stress in the solar cells. We also find that the interaction of the laminate with the module frame plays a significant role in thermal cycling. Of the varitations under investigation, the increase in cell size has the largest effect on the stress. However, at a mechanical load of 2400 Pa, glass-foil modules with less than 96 solar cells have a negligible failure probability. The advantage of placing the solar cells in the neutral axis of the laminate is proven by the negligible tensile stress values for all variations of the glass-glass modules.

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“…8,9 The In the first TMA heating run, all three types of encapsulants showed thermal expansion in both directions (machine direction MD and cross direction CD) indicating biaxial orientation, which is common in solar applications since it leads to better mechanical, optical and barrier properties. 52 However, for all test modules, yellowing was observed after DH test and the strongest for the material stacks using TPO as encapsulant (see Figure 7). Yellowing results from the presence of chromophoric groups in the polymer, which can be formed upon degradation of the polymer, the additives or unwanted reaction products thereof.…”

Section: Introductionmentioning

confidence: 91%

Properties and degradation behaviour of polyolefin encapsulants for photovoltaic modules

Oreški

Omazic

Eder

et al. 2020

Progress in Photovoltaics

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Various types of next-generation encapsulation films based on polyolefins have recently been introduced and could attract market attention. These material innovations can be classified as polyolefin elastomer (POE) and thermoplastic polyolefin (TPO) encapsulants, both of which consist of a polyethylene backbone with different side groups. The main advantage of these materials is the replacement of the vinyl acetate side groups of state-of-the-art encapsulant ethylene vinyl acetate (EVA) so that acetic acid cannot be formed. The main objective of this paper is to investigate the material properties of next-generation encapsulant films and compare them to an EVA reference. Two commercially available EVA alternatives (POE and TPO) have been selected. The material properties of single films as well as the electrical performance of test modules using these different encapsulants were investigated. The different films show comparable optical, thermal and thermo-mechanical properties, with slight differences in UV transparency and melting temperatures. Only shear viscosity values are higher for TPO than for POE and EVA, which requires adaption of the photovoltaic (PV) module lamination parameters. The test modules comprising the different encapsulation films show minor differences in the electrical performance after manufacturing; upon accelerated aging, no significant power loss is observed. But compared to TPO or POE, after 3000 h of damp heat exposure, test modules with EVA show the beginning of corrosion effects at the silver grid and above the ribbons. Based on the results, it can be stated that the new polyolefin encapsulation materials show great potential to be a valid replacement for EVA.

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Thermal expansion behavior of solar cell encapsulation materials

Cited by 29 publications

References 9 publications

Simple pretreatment processes for successful reclamation and remanufacturing of crystalline silicon solar cells

Simple pretreatment processes for successful reclamation and remanufacturing of crystalline silicon solar cells

The Effect of Cell and Module Dimensions on Thermomechanical Stress in PV Modules

Properties and degradation behaviour of polyolefin encapsulants for photovoltaic modules

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