Cyclic olefin polymer plates (Zeonex 350R®, Zeon) were first washed with ethanol (Roth, 99.8%) and then dried with dry air. In the next step, one side of the platelet was masked with peelable paint (Schmincke, Diaphoto film pelliculable rouge). Subsequently, the surface of the platelet was placed in a sputtering chamber and first activated with an O2 plasma (5 min, 5.5 sccm O2, 4 × 10 -3 mbar, 30 WRF). Subsequently, the SiO2 coating was prepared by radiofrequency (RF) magnetron sputtering. For this purpose, a SiO2 target (Lesker, 99.995% purity) and Ar (1 h, 9 sccm Ar, 4 × 10 -3 mbar, 100 WRF) were used. Dip coating (LayerBuilder, KSV) was used to deposit the photocatalytically active layer. The first photocatalyst was prepared from titanium dioxide powder (Aeroxide P25, Evonik Degussa), ethanol (Roth), and hydrochloric acid and was dispersed in ball mill (8 h at 400 rpm). After dispersion, 85 μL tetrabutyl orthotitanate (Aldrich) was added to the suspension and then stirred for 30 min at room temperature. The second photocatalyst was prepared from 0.5 M titanium tetraisopropoxide, water, and hydrochloric acid. The polymer platelets sputtered with SiO2 were immersed in the suspension, withdrawn with 60 mm s -1 , and then dried in a drying oven for 12 h at 80 °C. The UV-WLEs were prepared akin to the COP plates before dip coating, however, only the upper hemisphere of the WLEs (containing the LED and its emission area) was coated.