Using nanosecond laser pulses to debond the glass-EVA layer from silicon photovoltaic modules.

ABSTRACT

The active silicon cell of a solar photovoltaic (PV) panel is covered by an ethylenevinylacetate (EVA) adhesive and a protective top glass layer. Separating this glass-EVA layer from the underlying silicon represents a bottleneck for recycling PV panels. Previous work has shown that the EVA-Si bond can be weakened by applying a continuous source of heat to melt the EVA. In this paper, a new method using nanosecond laser pulses is demonstrated to induce transient melting selectively at the EVA-Si interface. This impulsive heating method can cleanly separate the glass-EVA layer from the silicon in both model and commercial multicrystalline PV panels. The dependence of this debonding on parameters like laser pulse fluence (laser pulse energy per area), wavelength, applied pressure, and scan speed were characterized. For model PV panels, the single-pulse laser fluences required for spontaneous separation of the assembly under the force of gravity, were 0.23, 0.32 and 0.78 J/cm2 for 355 nm, 532 nm and 1064 nm, respectively. The use of shorter wavelengths reduces the laser fluence needed for debonding, while higher fluences can compensate for faster laser beam scanning rates. Optical and electron microscopy images of the Si surfaces before and after laser irradiation show that the textured antireflection layer is destroyed but the silver metal grid remains intact. Preliminary experiments using 532 nm pulses showed that the laser debonding method could remove the glass-EVA layer from sections of decommissioned commercial PV panels, even when the top glass layer was densely cracked.