CdSe Quantum dot-conducting polymer hybrid structure for Phosphor-free white light-emitting diodes

A phosphor-free near-white-light-emitting diode (LED) is demonstrated by using a conducting polymer, poly(3, 4-ethylenedioxythiophene):poly(styrenesulphonic acid) (PEDOT:PSS) and a CdSe quantum dot (QD) composite layer that was fabricated by using a simple and inexpensive solution-based process. The PEDOT:PSS is deposited using a spin-coating method and shows an optical transmittance between 70 to 80% in the visible wavelength spectral range. The PEDOT:PSS embedding the CdSe QD composite layer shows a strong yellow emission at 587 nm. The electrical properties of an InGaN-based LED with PEDOT:PSS embedding CdSe QDs shows a forward operating voltage of 5.8 V, which is larger by 1.9 V compared to the voltage without the CdSe QDs. The electroluminescence spectra of an LED with PEDOT:PSS embedding CdSe QDs shows dual peaks at 447 and 580 nm, which are emitted from an InGaN quantum well and the CdSe QD layers, respectively. This indicates that the PEDOT:PSS embedding the CdSe QD composite layer acts as a transparent conducting electrode and a wavelength converter for white LED applications.