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Organic semiconductors are widely investigated for their application in photovoltaics and photodetectors. We show that the efficiency of these devices is strongly influenced by the position of the space charge region, due to unintentional doping, and wavelength-dependent absorption properties in bulk heterojunctions. Spray-coated P3HT:PCBM bulk heterojunction photodiodes with thicknesses up to 4.2 μm and semitransparent top contact enable the characterization of exciton generation and separation in both irradiation directions. A large difference in external quantum efficiency (EQE) is observed for top and bottom illuminated configurations and is explained by a bias dependent arrangement of the space charge region at the two contact electrodes. Numerical drift–diffusion simulations allow to get insight into first order mechanisms behind the spectral features of EQE data in highly-doped organic photodiodes. [ABSTRACT FROM AUTHOR]

We propose a model for short-channel organic thin-film transistors, which accounts for Poole-Frenkel field-dependent mobility and space-charge-limited current effects. The model is developed for devices operating in the linear regime, as well as in depletion and saturation regimes. Super linear output curves for low drain voltages, as well as nonsaturating currents, can be adequately described. Experimental results for short-channel P3HT devices have been fitted, showing good agreement with the proposed model. [ABSTRACT FROM AUTHOR]