We examine the impact of various parameters on the transient current density characteristics of organic solar cells and photodetectors by means of numerical simulations. Our self-consistent numerical model treats the dynamics of generated electrons and holes in the framework of a drift-diffusion model. As input parameter for the electric model, the intensity distribution of the incident light is calculated with a transfer-matrix method accounting for interference effects. The results are compared to experimental results. With our approach, we are able to distinguish the influence of different physical effects as they become dominant at different current densities or at different time regimes. This enables us to estimate the electron and hole mobilities separately by fitting the experimental results. Furthermore, space charge effects are identified as being highly important for the transient response of photodetectors.
The authors report the dynamic properties of bulk heterojunction photodiodes based on a polymer blend system consisting of poly(3-hexylthiophene-2,5-diyl) and the fullerene derivative [6,6]-phenyl C61-butyric acid methyl ester. Devices with a high-frequency contact layout were analyzed under continuous wave and pulsed laser illumination (λ=532nm). The organic photodiodes exhibit a pulse response with a full width at half maximum of 11ns to the applied 1.6-ns-long laser pulses. Rise times as small as 1.6ns and fall times <40ns were measured under applied reverse bias.
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