Fraunhofer Center for Silicon Photovoltaics CSP
Investigation on cracks of encapsulated solar cells
Cracks in solar cells are a common defect in PV modules. They reduce the module's performance and can lead to short circuits for extreme cases. For investigating such cracks a method was developed at Fraunhofer CSP with solar cells encapsulated in a PV laminate and defined mechanically boundary conditions and loading. For this purpose, a universal testing machine with 4-point-bending setup was coupled with an electroluminescence (EL) camera including an automatic test sequence. The mechanical load was progressively increased. At each load step an EL picture was shot to detect occurring cracks and correlate them to the exact load magnitudes. Combined with results from finite element analysis, each crack formation can be assigned to its corresponding tensile stress. As result the so called "in-laminate-strength" is calculated. It enables analysis of future module designs with innovative cells, glasses or encapsulants under defined laboratory conditions and prediction of cell cracks due to mechanical loading.
Investigation on optical quality and mechanical reliability of solar glas
In photovoltaic modules, glass is mainly used as a support structure and transparent enclosure. Here, its optical characteristics are significant for the efficiency of the PV module. In addition, the reliability of a PV module is strongly influenced by the strength of the glass. Current research activities are focusing on how the glass strength is influenced by the production steps during manufacturing of the PV modules.
Characterization of elastic properties and micro structural optimization of solar cell interconnectors using ultrasound
Characteristics of each component of solar modules are of great significance with respect to the module's reliability. Aim of this research is to measure mechanical properties (Young's modulus, Poisson's ration) of different components of PV modules using ultrasound and to monitor there properties during production.
Fatigue of solar cell interconnectors
Fatigue of solar cell interconnectors is a key failure mode for PV modules. An interconnection failure directly affects the series resistance and therefore leads to power loss, locally increased temperature and even security problems in operation (arcing). Loading of interconnectors occurs when cell displacement takes place due to temperature changes and mechanical loading of PV modules.
Fraunhofer CSP investigates the constitutive behaviour (stress-strain relationship) and fatigue behaviour of interconnector materials with specific experiments. The material data is further used in finite element models to estimate interconnector lifetime (cycles to failure) within a specific PV module under cyclic mechanical and thermo-mechanical loading.
Electrical conductive adhesives as solder alternative
Electrical conductive adhesives are a promising alternative to common solder technologies. Advantages are lower process temperatures (<150°C), relatively simple process technology with opportunity for automation and environmentally-friendly, since there is no lead and flux necessary. At Fraunhofer CSP all relevant properties can be characterized. The processing properties can be determined by thermo analytical methods (DSC, TMA, TGA, DMA). Structures for determination of volume resistance and contact resistance can be produced as needed. The mechanical properties of the adhesive joints are evaluated by standard peel-tests and special setups, which take the electrical properties into account.