@article{BangeSchubertNeher2010,
  author    = {Bange, Sebastian and Schubert, Marcel and Neher, Dieter},
  title     = {Charge mobility determination by current extraction under linear increasing voltages : case of nonequilibrium charges and field-dependent mobilities},
  issn      = {1098-0121},
  doi       = {10.1103/Physrevb.81.035209},
  year      = {2010},
  abstract  = {The method of current extraction under linear increasing voltages (CELIV) allows for the simultaneous determination of charge mobilities and charge densities directly in thin-film geometries as used in organic photovoltaic (OPV) cells. It has been specifically applied to investigate the interrelation of microstructure and charge-transport properties in such systems. Numerical and analytical calculations presented in this work show that the evaluation of CELIV transients with the commonly used analysis scheme is error prone once charge recombination and, possibly, field- dependent charge mobilities are taken into account. The most important effects are an apparent time dependence of charge mobilities and errors in the determined field dependencies. Our results implicate that reports on time-dependent mobility relaxation in OPV materials obtained by the CELIV technique should be carefully revisited and confirmed by other measurement methods.},
  language  = {en}
}
@article{SchubertSteyrleuthnerBangeetal.2009,
  author    = {Schubert, Marcel and Steyrleuthner, Robert and Bange, Sebastian and Sellinger, Alan and Neher, Dieter},
  title     = {Charge transport and recombination in bulk heterojunction solar cells containing a dicyanoimidazole-based molecular acceptor},
  issn      = {1862-6300},
  doi       = {10.1002/pssa.200925312},
  year      = {2009},
  abstract  = {Carrier transport and recombination have been studied in single component layers and blends of the soluble PPV- derivative poly[2,5-dimethoxy-1,4-phenylenevinylene-2-methoxy-5-(2-ethyl-hexyloxy)- 1,4-phenylenevinylene] (M3EH-PPV) and the small molecule acceptor 4,7-bis(2-(1-hexyl-4,5-dicyanoimidazole-2-yl)vinyl) benzo[c][1,2,5]-thiadiazole (HV-BT). Measurements on single carrier devices show significantly smaller electron mobility in the blend compared to the pure HV- BT layer, which is suggestive of the formation of isolated clusters of the acceptor in a continuous polymer matrix. The significant change in fill factor (FF) with increasing illumination intensity is consistently explained by a model taking into account bimolecular recombination and space charge effects. The decay of the carrier density after photoexcitation has been studied by performing photo-CELIV measurements on pure and blend layers. It is found that the decay at long delay times follows a power-law dependence, which is, however, not consistent with a Langevin-type bimolecular recombination of free charges. A good description of the data is obtained by assuming trimolecular recombination to govern the charge carrier dynamics in these systems.},
  language  = {en}
}
@article{SchubertYinCastellanietal.2009,
  author    = {Schubert, Marcel and Yin, Chunhong and Castellani, Mauro and Bange, Sebastian and Tam, Teck Lip and Sellinger, Alan and Hoerhold, Hans-Heinrich and Kietzke, Thomas and Neher, Dieter},
  title     = {Heterojunction topology versus fill factor correlations in novel hybrid small-molecular/polymeric solar cells},
  issn      = {0021-9606},
  doi       = {10.1063/1.3077007},
  year      = {2009},
  abstract  = {The authors present organic photovoltaic (OPV) devices comprising a small molecule electron acceptor based on 2- vinyl-4,5-dicyanoimidazole (Vinazene (TM)) and a soluble poly(p-phenylenevinylene) derivative as the electron donor. A strong dependence of the fill factor (FF) and the external quantum efficiency [incident photons converted to electrons (IPCE)] on the heterojunction topology is observed. As-prepared blends provided relatively low FF and IPCE values of 26\% and 4.5\%, respectively, which are attributed to significant recombination of geminate pairs and free carriers in a highly intermixed blend morphology. Going to an all-solution processed bilayer device, the FF and IPCE dramatically increased to 43\% and 27\%, respectively. The FF increases further to 57\% in devices comprising thermally deposited Vinazene layers where there is virtually no interpenetration at the donor/acceptor interface. This very high FF is comparable to values reported for OPV using fullerenes as the electron acceptor. Furthermore, the rather low electron affinity of Vinazene compound near 3.5 eV enabled a technologically important open circuit voltage (V-oc) of 1.0 V.},
  language  = {en}
}
@article{SteyrleuthnerBangeNeher2009,
  author    = {Steyrleuthner, Robert and Bange, Sebastian and Neher, Dieter},
  title     = {Reliable electron-only devices and electron transport in n-type polymers},
  issn      = {0021-8979},
  doi       = {10.1063/1.3086307},
  year      = {2009},
  abstract  = {Current-voltage analysis of single-carrier transport is a popular method for the determination of charge carrier mobilities in organic semiconductors. Although in widespread use for the analysis of hole transport, only a few reports can be found where the method was applied to electron transport. Here, we summarize the experimental difficulties related to the metal electrode leakage currents and nonlinear differential resistance (NDR) effects and explain their origin. We present a modified preparation technique for the metal electrodes and show that it significantly increases the reliability of such measurements. It allows to produce test devices with low leakage currents and without NDR even for thin organic layers. Metal oxides were often discussed as a possible cause of NDR. Our measurements on forcibly oxidized metal electrodes demonstrate that oxide layers are not exclusively responsible for NDR effects. We present electron transport data for two electron-conducting polymers often applied in all-polymer solar cells for a large variety of layer thicknesses and temperatures. The results can be explained by established exponential trapping models.},
  language  = {en}
}