We examine the impact of various annihilation processes on the laser threshold current density of a multilayer organic laser diode by numerical simulation. Our self-consistent numerical model treats the dynamics of electrons, holes, and singlet as well as triplet excitons in the framework of a drift-diffusion model. The resulting particle distributions enter into an optical model. In our approach, a three layer waveguide structure is taken into account and the resulting laser rate equations are solved. Various annihilation processes are included as reactions between the different particle species in the device employing typical annihilation rates and material properties of organic semiconductors. By systematically varying the device dimensions and the annihilation rate coefficients, the dominating quenching processes are identified. The threshold current density is found to depend sensitively on the thickness of the emission layer. The influence of annihilation processes on the threshold current density is quantified as a function of the emission layer thickness and various annihilation rate coefficients. Using typical annihilation rate coefficients singlet-polaron annihilation is found to be the dominating quenching process. Maximum annihilation rate coefficients are calculated allowing a threshold current density below 1kA∕cm2. Singlet-triplet annihilation is recognized as another main loss process for singlet excitons. In our model the singlet exciton density is increased by triplet-triplet annihilation whereas it is diminished by singlet-triplet annihilation. The ratio of the rate coefficients for singlet-triplet and triplet-triplet annihilations is identified to be critical for the total number of singlet excitons being quenched by triplet excitons.

The authors present organic semiconductor distributed feedback lasers based on thin films of the conjugated polymer poly[9,9-dioctylfluorene-co-9,9-di(4-methoxy-phenyl)fluorene] and employing an improved resonator design. In order to combine the advantages of first- and second-order distributed feedback resonators, the authors utilize a mixed-order grating design: A second-order Bragg scattering region that provides efficient vertical outcoupling of the laser radiation is surrounded by first-order scattering regions that give rise to strong feedback. By optimizing the film thickness to obtain laser oscillation at the polymer maximum gain wavelength, a very low laser threshold of 45pJ∕pulse (≈36nJ∕cm2) was realized with this resonator concept.

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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