Low driving voltage in polymer light-emitting diodes with CdS nanoparticles as an electron transport layer

Water-soluble cadmium sulfide (CdS) nanoparticles were synthesized through aqueous thermochemical method using thioglycolic acid as a capping agent. The resulting CdS nanoparticles were characterized using x-ray diffraction, field-emission scanning electron microscopy, ultraviolet-visible, and photoluminescence spectroscopy. The CdS prepared has been used as an electron transport layer (ETL) in a polymer light-emitting diode (PLED) with the structure of poly(ethylene terephthalate)/indium tin oxide/poly(3,4-ethylenedioxythiophene): polystyrene sulfonate/poly[2-methoxy-5-(2 '-ethyl-hexyloxy)-1,4-phenylene vinylene/CdS/aluminium (PET/ITO/PEDOT:PSS/MEH-PPV/CdS/Al). The performance of the fabricated device containing CdS nanoparticles as an ETL was compared with the device with the structure of PET/ITO/PEDOT: PSS/MEH-PPV/Al. According to the obtained results, it was shown that the ETL yields a higher current and lower turn-on voltage. The improvement was ascribed to the step barrier theory and hole blocking effect of the CdS layer. These results show that the CdS layer could be very useful in the fabrication of efficient PLEDs. (C) 2015 Society of Photo-Optical Instrumentation Engineers (SPIE)