Device Fabrication. The substrates for LEDs, sized 2x2 cm and coated with 90nm structured Indium tin oxide (ITO), were purchased from Kintec (Hong Kong). Initially, PEDOT:PSS was spin-coated in the cleanroom on top of the structured ITO substrates, at 4000 rpm for 30 s, and heated on a hot plate at 130 °C for 15 min, resulting in a smooth, approximately 40 nm thin film.