Relaxation of photogenerated Carrieres in P3HT PCBM Organic Blends

The after pulse time resolved microwave conductivity TRMC decays observed in P3HT PCBM blends display a dependence on time close to t b, independent of excitation intensity, in the 10 ns 1 ms range. This is explained in terms of the relaxation of carriers in a Gaussian density of states DOS . The model is based on a demarcation level that moves with time by thermal release and retrapping of initially trapped carriers. The model shows that when the disorder is large the after pulse decay of the type t b is obtained, while at low disorder and large temperature the carrier distribution becomes independent of time. In the measurements different b values were observed depending on the solvent used for spin coating 0.4 0.6 for chlorobenzene and 0.3 0.4 for toluene. The model was applied to extract the shape of the DOS from the TRMC decays, giving a dispersion parameter of about 120 meV for blends with high P3HT conten

Universal transients in polymer and ionic transition metal complex light-emitting electrochemical cells

Two types of light-emitting electrochemical cells (LECs) are commonly distinguished, the polymer-based LEC (p-LEC) and the ionic transition metal complex-based LEC (iTMC-LEC). Apart from marked differences in the active layer constituents, these LEC types typically show operational time scales that can differ by many orders of magnitude at room temperature. Here, we demonstrate that despite these differences p-LECs and iTMC-LECs show current, light output, and efficacy transients that follow a universal shape. Moreover, we conclude that the turn-on time of both LEC types is dominated by the ion conductivity because the turn-on time exhibits the same activation energy as the ion conductivity in the off-state. These results demonstrate that both types of LECs are really two extremes of one class of electroluminescent devices. They also implicate that no fundamental difference exists between charge transport in small molecular weight or polymeric mixed ionic and electronic conductive materials. Additionally, it follows that the ionic conductivity is responsible for the dynamic properties of devices and systems using them. This likely extends to mixed ionic and electronic conductive materials used in organic solar cells and in a variety of biological systems

Universal transients in polymer and ionic transition metal complex light-emitting electrochemical cells

Two types of light-emitting electrochemical cells (LECs) are commonly distinguished, the polymer-based LEC (p-LEC) and the ionic transition metal complex-based LEC (iTMC-LEC). Apart from marked differences in the active layer constituents, these LEC types typically show operational time scales that can differ by many orders of magnitude at room temperature. Here, we demonstrate that despite these differences p-LECs and iTMC-LECs show current, light output, and efficacy transients that follow a universal shape. Moreover, we conclude that the turn-on time of both LEC types is dominated by the ion conductivity because the turn-on time exhibits the same activation energy as the ion conductivity in the off-state. These results demonstrate that both types of LECs are really two extremes of one class of electroluminescent devices. They also implicate that no fundamental difference exists between charge transport in small molecular weight or polymeric mixed ionic and electronic conductive materials. Additionally, it follows that the ionic conductivity is responsible for the dynamic properties of devices and systems using them. This likely extends to mixed ionic and electronic conductive materials used in organic solar cells and in a variety of biological systems

Dynamic doping in planar ionic transition metal complex-based light-emitting electrochemical cells

Using a planar electrode geometry, the operational mechanism of iridium(III) ionic transition metal complex (iTMC)-based light-emitting electrochemical cells (LECs) is studied by a combination of fluorescence miscroscopy and scanning Kelvin probe microscopy (SKPM). Applying a bias to the LECs leads to the quenching of the photoluminescence (PL) in between the electrodes and to a sharp drop of the electrostatic potential in the middle of the device, far away from the contacts. The results shed light on the operational mechanism of iTMC-LECs and demonstrate that these devices work essentially the same as LECs based on conjugated polymers do, i.e., according to an electrochemical doping mechanism. Moreover, with proceeding operation time the potential drop shifts towards the cathode coincident with the onset of light emission. During prolonged operation the emission zone and the potential drop both migrate towards the anode. This event is accompanied by a continuous quenching of the PL in two distinct regions separated by the emission line