RESUMO
Surface-emitting organic light-emitting transistors (OLETs) could well be a core element in the next generation of active-matrix (AM) displays. We report some of the key characteristics of graphene-based vertical-type organic light-emitting transistors (Gr-VOLETs) composed of a single-layer graphene source and an emissive channel layer. It is shown that FeCl3 doping of the graphene source results in a significant improvement in the device performance of Gr-VOLETs. Using the FeCl3-doped graphene source, it is demonstrated that the full-surface electroluminescent emission of the Gr-VOLET can be effectively modulated by gate voltages with high luminance on/off ratios (~104). Current efficiencies are also observed to be much higher than those of control organic light-emitting diodes (OLEDs), even at high luminance levels exceeding 500 cd/m2. Moreover, we propose an operating mechanism to explain the improvements in the device performance i.e., the effective gate-bias-induced modulation of the hole tunnelling injection at the doped graphene source electrode. Despite its inherently simple structure, our study highlights the significant improvement in the device performance of OLETs offered by the FeCl3-doped graphene source electrode.
RESUMO
High electrical conductivity of metal oxide thin films needs uniform surface coverage, which has been the issue for the thin films based on electrospun nanofibers (NFs) that have advantage over the sputtered/spin-coated films with respect to large surface area and mechanical flexibility. Herein, we investigated a reduction in the sheet resistance of electrospun indium tin oxide (ITO) NF films with improved surface coverage. We found that the surface coverage depends significantly on the electrospinnable polymer concentration in the precursor solutions, especially after post-hot-plate annealing following the infrared radiation furnace treatment. The postannealing process increases crystallinity and oxygen vacancies. However, with a higher PVP content, it makes the surface of ITO NFs more prominently rough as a result of the formation of larger sphere-shaped ITO particles on the NF surface, which gives rise to poor surface coverage. A less poly(vinylpyrrolidone) (PVP) content in ITO NF films by electrospinning for short deposition times was found to improve surface coverage even after postannealing. The sheet resistance notably decreases, down to as low as 350 Ω/sq, with a high transmittance of over 90%. Our study provides an understanding on how to achieve high electrical conductivity of ITO NF films with high surface coverage, which can be utilized for the optoelectronic and sensing applications.
