Showing papers by "Peter Hacke published in 2010"

Characterization of Multicrystalline Silicon Modules with System Bias Voltage Applied in Damp Heat

Abstract: Because it is considered economically favorable to build arrays with high system voltage by serially connecting photovoltaic (PV) modules, it is necessary to explore the potential long-term degradation mechanisms that the modules may incur under such electrical potential. We performed accelerated lifetime testing of multicrystalline silicon PV modules in 85°C/85% relative humidity (RH) and 45°C/30% RH while placing the active layer in either positive or negative 600 V bias with respect to the grounded module frame. A negative bias applied to the active layer leads to more rapid and catastrophic module power degradation compared to a positive bias. This negative bias degradation is associated with significant shunting of individual cells as indicated by electroluminescence, thermal imaging, and I-V curves. Mass spectroscopy results support ion migration as one of the causes. Electrolytic corrosion is seen occurring with the silicon nitride antireflective coating and silver gridlines, and there is ionic transport of metallization at the encapsulant interface observed with damp heat and applied bias. Leakage current and module degradation are found to be highly dependent on the module construction, with factors such as encapsulant and front glass resistivity affecting performance. Measured leakage currents range from about the same as those seen in published reports of modules deployed in Florida (USA) to about 100 times higher when undergoing environmental chamber testing.

Test-to-Failure of crystalline silicon modules

Abstract: Accelerated lifetime testing of five crystalline silicon module designs was carried out according to the Terrestrial Photovoltaic Module Accelerated Test-to-Failure Protocol. This protocol compares the reliability of various module constructions on a quantitative basis. The modules under test are subdivided into three accelerated lifetime testing paths: 85°C/85% relative humidity with system bias, thermal cycling between −40°C and 85°C, and a path that alternates between damp heat and thermal cycling. The most severe stressor is damp heat with system bias applied to simulate the voltages that modules experience when connected in an array. Positive 600 V applied to the active layer with respect to the grounded module frame accelerates corrosion of the silver grid fingers and degrades the silicon nitride antireflective coating on the cells. Dark I–V curve fitting indicates increased series resistance and saturation current around the maximum power point; however, an improvement in junction recombination characteristics is obtained. Severe shunt paths and cell-metallization interface failures are seen developing in the silicon cells as determined by electroluminescence, thermal imaging, and I–V curves in the case of negative 600 V bias applied to the active layer. Ability to withstand electrolytic corrosion, moisture ingress, and ion drift under system voltage bias are differentiated according to module design. The results are discussed in light of relevance to field failures.

Back contact solar cells having exposed vias

Abstract: Embodiments of the invention contemplate the formation of a solar cell device that has improved efficiency and device electrical properties. In one embodiment, the solar cell device described herein includes an Emitter Wrap Through (EWT) solar cell that has plurality of laser drilled vias disposed in a spaced apart relationship to metal gridlines formed on a surface of the substrate. Solar cell structures that may benefit from the invention disclosed herein include back-contact solar cells, such as those in which both positive and negative contacts are formed only on the rear surface of the device.