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20 The PCB Magazine • June 2014 approach offers advantages in practical areas of surface performance, appearance and viewing angle distortion. Participation in the European funded FP7 programme FLEX-o-FAB has brought optical outcoupling and clean substrate technology to the other participants with a goal of develop- ing a cost-effective R2R process route to flex- ible OLED lighting. The principle of emission enhancement for flexible OLED using a flexible polyester substrate with integrated volume scat- tering features has already been demonstrated. The efficacy increased from 30 lm/W to 42 lm/W by using barrier foil with integrated out- coupling enhancement. 4. Weatherable Films Polyesters such as PET and to a lesser ex- tent PEN are inherently susceptible to degra- dation by hydrolysis. However, the hydro- lysis behaviour of PET film can be improved significantly by control of variables such as molecular weight, the crystallinity developed during the filming process and by control of SUBSTRATES: PoLyESTER FILM FoR THE FLExIBLE ELECTRoNICS INDUSTRy continues Figure 5: cyclic oligomer "bloom" on typical Pet and Pen film surfaces after aging. Figure 6: angle dependent color/emission from glass oled using outcoupling overlaminate (courtesy of Holst centre, eindhoven).