The article by Liu et al. goes exactly in this direction; it describes a relatively simple technique to improve the OLEDs’ lightextraction efficiency by placing a film with bulk and surface micropores at the air–glass interface. In fact, the typical structure of an OLED, consisting of several layers of organic materials deposited over a flat glass substrate, is intrinsically prone to trap light inside it by total internal reflection (waveguiding). Usually, the best way to cope with this problem is to modify the interface between the air and the glass substrate, for example by corrugating this interface in some way or making an array of microlenses. This approach has the significant advantage of not interfering with the deposition of the organic materials on the other side of the device. However, various techniques for implementing this air–substrate interface modification studied before this work were not well suited for mass production, since they required repeated steps of lithography and curing of the samples. The technique devised by Liu et al. seems to overcome this problem completely: by creation of a microporous film at this critical interface by exploiting the spontaneous polymer phase separation of a blended solution of inexpensive polystyrene and polyethylene glycol during the drying process. The results reported by the authors are impressive, since they claim to have measured an optical coupling efficiency enhancement factor of 60%.
In conclusion, it is difficult to overestimate the importance of this research for the development of inexpensive OLEDs suitable for mass production. The time is coming when we will begin to harvest the huge benefits of this new technology.
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