Degradation of interfacial adhesion strength within photovoltaic mini-modules during damp-heat exposure

• Published in: Progress in photovoltaics Vol. 22; no. 7; pp. 796 - 809
• Main Authors: Wu, Dan, Zhu, Jiang, Betts, Thomas R., Gottschalg, Ralph
• Format: Journal Article Conference Proceeding
• Language: English
• Published: Bognor Regis Blackwell Publishing Ltd 01.07.2014; Wiley; Wiley Subscription Services, Inc
• Subjects: adhesion strength; Adhesive strength; Applied sciences; damp heat; Degradation; Energy; Equipments, installations and applications; Exact sciences and technology; Humidity; humidity dose; Mathematical models; Natural energy; peel test; Photovoltaic cells; Photovoltaic conversion; Relative humidity; Solar cells; Solar cells. Photoelectrochemical cells; Solar energy; Strength; Relative humidity; Peel test; Photovoltaic system; humidity dose; Adhesion; Linear model; Degradation; Crystalline material; Humidity effect; adhesion strength; Decay time; Photovoltaic array; damp heat; Time interval; Silicon; Delamination; Activation energy; Stretching; Damaging
• ISSN: 1062-7995; 1099-159X
• DOI: 10.1002/pip.2460

ABSTRACTThe degradation of adhesion strength between the back sheet and encapsulant due to moisture penetration has been investigated for commercial crystalline silicon photovoltaic mini‐modules. The damp‐heat tests originating from the International Electrotechnical Commission qualification test were carried out at five different temperature and relative humidity (RH) conditions (95 °C/85% RH, 85 °C/85% RH, 65 °C/85% RH, 85 °C/65% RH and 85 °C/45% RH). The adhesion strength was measured by 90° peel tests, carried out at specified time intervals during degradation. Several visible defects were observed, including delamination, moisture ingress and bubble formation. The adhesion strength showed a stretched exponential decay with time, and significant influence of test conditions was demonstrated. A humidity dose model was proposed by assuming micro‐climates seen by the modules, that is, surface relative humidity of the back sheet as the driving factor for an Arrhenius‐based model using temperature as accelerating factor. The correlation between adhesion strength degradation and humidity dose was investigated through linear and exponential models. Results showed that the conventional linear model failed to represent the relationship while the exponential model fitted to this correlation with extracted activation energy (Ea) of around 63 kJ/mol. This provides a model for the estimation of adhesion strength decay in dependence of the humidity conditions. © 2014 The Authors. Progress in Photovoltaics: Research and Applications published by John Wiley & Sons, Ltd. Peel tests between the back sheet and encapsulant of commercial mini‐modules were conducted at five different damp‐heat conditions. A humidity dose model was proposed to describe the cumulative stresses experienced by the module within a certain time period by assuming surface relative humidity of the back sheet as the driving factor for an Arrhenius‐based model using temperature as accelerating factor. The adhesion strength demonstrated an exponential decay with humidity dose. This study contributes to the estimation of adhesion reliability in outdoor conditions.