Laser-assisted dry, wet texturing and phase transformation of flexible polyethylene terephthalate substrate revealed by Raman and ultraviolet-visible spectroscopic studies

Abstract

A systematic understanding of laser-induced texturing and its influence on the local structural change in polyethylene terephthalate (PET) substrate offers enhanced performance characteristics of photovoltaic devices. The formation of multiple phases in flexible PET substrate using selective processing by means of laser-assisted heat input reveals enhanced ultraviolet-visible (UV-Vis) absorption. The authors investigate the characteristics of multiple phases formed during the interaction of the laser pulse on the PET substrate processed under dry and wet environments. It is observed that the laser beam profile is replicated on the substrate during wet environment. Moreover, the heat gradient of laser beam have induced various indexed crystalline phases as revealed by Raman spectroscopy as well as their optical characteristics of replicated profile on PET substrate is quantified using UV-Vis absorption spectroscopy. Furthermore, a redshift in the absorption measured at the center of the projected beam profile is attributed to the higher degree of ordered crystalline phase as compared to other graded phases inside the trench. These findings of phase gradients and their influence on optical properties of laser-induced texturing would be useful for laser-based rapid texturing for flexible photovoltaics.