I used to make blue ones of novel polymers.... polymers which even I would be hesitant to make at home....volatile Ni(0) catalysts...ew
But you can buy polydioctylfluorene, a blue emitter, and spincoat(tape substrate to a PC fan) it on transparent conducting oxide plates, and make the other electrode by exploding some wire ontop. Of course you can get more hardcore by adding a layer of PEDOT.PSS which slows either holes or e-, I forget, in any case it makes the holes and e- recombine in the polymer layer making for a brighter device.