Polymeric Transport Layer Research Articles

Effect of doping of zinc oxide on the hole mobility of poly(3-hexylthiophene) in hybrid transistors

Hybrid field effect transistors based on the organic polymer poly(3-hexylthiophene) (P3HT) and inorganic zinc oxide were investigated. In this report we present one of the first studies on hybrid transistors employing one polymeric transport layer. The sol–gel processed ZnO was modified via Al doping between 0.8 and 10 at.%, which allows a systematic variation of the zinc oxide properties, i.e. electron mobility and morphology. With increasing doping level we observe on the one hand a decrease of the electron mobilities by two orders of magnitude, on the other hand doping enforces a morphological change of the zinc oxide layer which enables the infiltration of P3HT into the inorganic matrix. X-ray reflectivity (XRR) measurements confirm this significant change in the interface morphology for the various doping levels. We demonstrate that doping of ZnO is a tool to adjust the charge transport in ZnO/P3HT hybrids, using one single injecting metal (Au bottom contact) on a SiO 2 dielectric. We observe an influence of the zinc oxide layer on the hole mobility in P3HT which we can modify via Al doping of ZnO. Hence, maximum hole mobility of 5 · 10 - 4 cm 2 V - 1 s - 1 in the hybrid system with 2% Al doping. 5 at.% Al doping leads to a balanced mobility in the organic/inorganic hybrid system but also to a small on/off ratio due to high off-currents.

The role of interface in photo processes in photoconductive heterophase composites based on monolayer dispersions of molybdenum disulfide

Two-layer heterostructures with a high yield of charged current carriers were obtained and investigated. The heterostructures comprised monolayer dispersions of MoS2 in polyvinyl alcohol as the lower layer and the upper p-, n-, or bipolar transport layer (TL). It was found that dark conductivity of the two-layer heterostructures increased considerably compared with the conductivity of reference samples based on TL but containing no MoS2. After excitation from the TL side, maximum photoelectric sensitivity was obtained where TL long-wave absorption decreased and there was a high concentration of TL excited states at the interface that interacted with the surface of MoS2 particles. This interaction quenched the luminescence of TL transport centers and led to the photogeneration of both positively and negatively charged current carriers at the interface. Luminescence quenching could be of 50–60% at high MoS2 contents in the lower layer (90–100 wt %). This was evidence that the contact area of MoS2 particles with the polymeric transport layer exceeded the geometric interface dimensions and the interface had a relief surface (was fairly thick). It was found that the donor-acceptor properties of both MoS2 and the polymeric TL were very important for the photogeneration of charge carriers at the interface. When the MoS2 content in the lower layer was maximum, the effectiveness of the accumulation of minority carriers increased because of the formation of an alternative transport network associated with MoS2 particles. The conclusion was drawn that the photogeneration of charges at the interface resulted from the phototransfer of electrons between MoS2 particles and TL excited states.

Ligand-Accelerated Catalysis of the Ullmann Condensation: Application to Hole Conducting Triarylamines

Ligand-Accelerated Catalysis of the Ullmann Condensation: Application to Hole Conducting Triarylamines