Expanded Electroluminescence in High Load CdS Nanocrystals PVK-Based LEDs

Abstract

Immiscibility between dimethyl sulfoxide (DMSO) and polar solvents used for poly(N-vinylcarbazole) (PVK) solutions, leads to failed light-emitting diodes when colloidal cadmium sulfide (CdS) nanoparticles capped with thiophenol are incorporated to their active layer. To prevent this, a heat treatment is applied to the CdS nanoparticles in order to evaporate DMSO solvent. After evaporation most of the nanoparticles increased their size, and some of them show hexagonal crystalline structure instead of the original cubic zinc-blende observed in colloidal pre-treated nanoparticles. Nevertheless, enhanced electronic properties are measured in light-emitting devices when DMSO-free nanoparticles are embedded in the poly(N-vinylcarbazole) active layer. Light emission from these hybrid devices comprises the whole visible range of wavelengths as searched for white LEDs. Moreover, electroluminescence from both types of CdS nanoparticles (smaller cubic and bigger hexagonal) has been discriminated and interpreted through Gaussian deconvolution.

Novel Dicyano-Phenylenevinylene Fluorophores for Low-Doped Layers: A Highly Emissive Material for Red OLEDs

“…In Figure 4, the current density–voltage characteristic of the device is reported. The turn-on voltage was approximately 3.5 V. The current density magnitude was quite low with respect to analogous devices reported in the literature [50], probably because the thickness of the layers was not optimized in the device structure. Moreover, since the measurements were performed in air soon after the evaporation, the degradation of the Ca/Al cathode could have affected the series resistance of the whole device, further limiting the current density.…”

“…The optical turn-on voltage was around 7 V. Also, the absolute values of the luminance were affected by the limitation of the current density. Interestingly, the current efficiency (calculated as the slope of the line in Figure 6) was a value that can be considered as a state-of-the-art PVK-doped layer (0.44 cd/A) [50]. In fact, the current efficiency was only slightly decreased with respect to a pristine PVK active layer due to the addition of C1 dye, probably because of our good PLQY, especially considering the case of doped emissive layers [50].…”

“…Interestingly, the current efficiency (calculated as the slope of the line in Figure 6) was a value that can be considered as a state-of-the-art PVK-doped layer (0.44 cd/A) [50]. In fact, the current efficiency was only slightly decreased with respect to a pristine PVK active layer due to the addition of C1 dye, probably because of our good PLQY, especially considering the case of doped emissive layers [50]. In Figure 7, the normalized electroluminescence intensity versus wavelength is reported, as well as the corresponding very similar PL spectrum of the C1-PVK blend.…”

A Comparative Study of Theoretical Methods to Estimate Semiconductor Nanoparticles’ Size

“…The commented aberrations limit the resolution of our TEM device to 0.19 nm. This resolution is smaller than the space of (200) family planes used as a references for the nanoparticles' measurements [18].…”

Special Issue “II-VI Semiconductor Nanocrystals and Hybrid Polymer–Nanocrystal Systems”

“…In their paper, F. Rodríguez-Mas et al [ 5 ] discuss the possible development of hybrid polymer–NC active films for LEDs. In particular, the authors investigate the possibility of mixing in a single layer poly(N-vinylcarbazole) (PVK) and colloidal CdS NCs capped with thiophenol in order to realize hybrid LEDs with engineered electrical properties and tunable electroluminescence spectra.…”