Permanent Electrochemical Doping of Quantum Dots and Semiconductor Polymers

Arguably the most controllable way to control the charge density in various semiconductors, is by electrochemical doping. However, electrochemically injected charges usually disappear within minutes to hours, which is why this technique is not yet used to make semiconductor devices. In this manuscript, electrochemical doping of different semiconductor films (ZnO Quantum Dots (QDs), PbS QDs, and P3DT) is investigated in various high melting-point nitrile-based solvents. It is shown that by charging the semiconductors at elevated temperatures, then cooling down to room temperature where these solvents are frozen, the doping stability increases immensely. Measurements performed in cyanoacetamide show that ion transport is entirely halted at room temperature, and that the n-type conductivity is stable for days, and only drops marginally (≈10%) in several weeks. For p-doped P3DT films, the conductivity is even completely stable during the entire 76 days of the measurement. In an ambient atmosphere, the p-type doping is stable, while the n-type doping disappears in several hours, as electrons react with molecular oxygen. Finally, a pn-junction diode made of a PbS QD film is demonstrated. These results highlight the possibility of using solidified electrolytes for electrochemical doping and for obtaining semiconductor devices wherein the doping density is controlled electrochemically.ChemE/Opto-electronic Material

Enhancing the Stability of the Electron Density in Electrochemically Doped ZnO Quantum Dots

Electronic doping of semiconductor nanomaterials can be efficiently achieved using electrochemistry. However, the injected charge carriers are usually not very stable. After disconnecting the cell that is used for electrochemical doping the carrier density drops, typically in several minutes. While there are multiple possible causes for this, we demonstrate here, using n-doped ZnO quantum-dot films of variable thickness that the dominant mechanism is reduction of solvent impurities by the injected electrons. We subsequently investigate two different ways to enhance the doping stability of ZnO QD films. The first method uses preemptive reduction of the solvent impurities; the second method involves a solid covering the QD film, which hinders impurity diffusion to the film. Both methods enhance the doping stability of the QD films greatlyChemE/Opto-electronic Material

The Role of Dopant Ions on Charge Injection and Transport in Electrochemically Doped Quantum Dot Films

Control over the charge density is very important for implementation of colloidal semiconductor nanocrystals into various optoelectronic applications. A promising approach to dope nanocrystal assemblies is charge injection by electrochemistry, in which the charge compensating electrolyte ions can be regarded as external dopant ions. To gain insight into the doping mechanism and the role of the external dopant ions, we investigate charge injection in ZnO nanocrystal assemblies for a large series of charge compensating electrolyte ions with spectroelectrochemical and electrochemical transistor measurements. We show that charge injection is limited by the diffusion of cations in the nanocrystal films as their diffusion coefficient are found to be ∼7 orders of magnitude lower than those of electrons. We further show that the rate of charge injection depends strongly on the cation size and cation concentration. Strikingly, the onset of electron injection varies up to 0.4 V, depending on the size of the electrolyte cation. For the small ions Li+ and Na+ the onset is at significantly less negative potentials. For larger ions (K+, quaternary ammonium ions) the onset is always at the same, more negative potential, suggesting that intercalation may take place for Li+ and Na+. Finally, we show that the nature of the charge compensating cation does not affect the source-drain electronic conductivity and mobility, indicating that shallow donor levels from intercalating ions fully hybridize with the quantum confined energy levels and that the reorganization energy due to intercalating ions does not strongly affect electron transport in these nanocrystal assemblies.ChemE/Opto-electronic MaterialsChemE/Chemical EngineeringBN/Technici en Analiste

Musculoskeletal pain and its effect on daily activity and behaviour in Icelandic children and youths with juvenile idiopathic arthritis: a cross-sectional case-control study

Abstract Background Juvenile idiopathic arthritis is characterised by recurring episodes of acute inflammation, with joint swelling in one or more joints, often accompanied by pain. These episodes can now be controlled better than in the past because of a new category of medications. However, despite more stable disease activity, pain may continue to cause problems in the children with juvenile idiopathic arthritis and can reduce their performance of routine physical activities and participation in social or school activities. Aim To evaluate the prevalence of pain, pain intensity, pain behaviour, and pain interference in Icelandic children with juvenile idiopathic arthritis compared with healthy peers. Methods A cross-sectional, case-control study including 8-18 years old children; 28 with juvenile idiopathic arthritis and 36 in a control group. The children answered questions on pain experienced during the last 7 days, painful areas of the body and pain frequency. They completed short form versions of the Patient-Reported Outcome Measurement Information System (PROMIS) questionnaires on pain intensity, pain behaviour, and pain interference. Results Significantly more children with juvenile idiopathic arthritis had pain compared with the control group (p = 0.02). Children with JIA also had a greater number of painful body areas (p = 0.03), more pain intensity (p = 0.009), and showed more pain behaviour (p = 0.006), and pain interference (p = 0.002). Children with juvenile idiopathic arthritis who had pain, experienced more pain interference (p = 0.023) than their peers who had pain. However, the groups did not differ in terms of pain intensity (p = 0.102) and pain behaviour (p = 0.058). Conclusion The research results indicate that pain experience was different between children with juvenile idiopathic arthritis and the control group. The results suggest that further research of the role of pain management on functional outcomes in children with juvenile idiopathic arthritis is needed