Drift and Diffusion in Disordered Organic Semiconductors: The Role of Charge Density and Charge Energy Transport

Using Monte Carlo simulations, we revisited charge transport in degenerate disordered organic semiconductors that are characterized by hopping transport. We found that, when a non-negligible fraction of the molecules is ionized (i.e., high charge density), charge transfer (transport) involves transfer of energy as well. Although Monte Carlo simulations confirm that, at low electric fields, the generalized Einstein relation describes the relation between drift and diffusion well, the use of the energy flux model provides a more intelligible and transparent description of the phenomenon at hand, enabling its generalization under the same premise as the thermoelectric effect and establishing a basis for the monitoring of charge-carrier energy trajectories within the traversed media.

[1]  N. Tessler,et al.  Spatially dispersive transport: A mesoscopic phenomenon in disordered organic semiconductors , 2007 .

[2]  Y. Eichen,et al.  Charge Density and Film Morphology Dependence of Charge Mobility in Polymer Field‐Effect Transistors , 2003 .

[3]  Noam Rappaport,et al.  The mobility spatial distribution function: Turn-on dynamics of polymer photocells , 2006 .

[4]  D. Vanmaekelbergh,et al.  Wide energy-window view on the density of states and hole mobility in poly(p-phenylene vinylene). , 2004, Physical review letters.

[5]  P. Heremans,et al.  Analytic model of hopping mobility at large charge carrier concentrations in disordered organic semiconductors: Polarons versus bare charge carriers , 2007 .

[6]  Noam Rappaport,et al.  Charge Transport in Disordered Organic Materials and Its Relevance to Thin‐Film Devices: A Tutorial Review , 2009 .

[7]  J. Bisquert.  Interpretation of electron diffusion coefficient in organic and inorganic semiconductors with broad distributions of states. , 2008, Physical chemistry chemical physics : PCCP.

[8]  S. Baranovskii,et al.  Concentration dependence of the transport energy level for charge carriers in organic semiconductors , 2010 .

[9]  R. Stratton,et al.  Semiconductor current-flow equations (diffusion and degeneracy) , 1972 .

[10]  E. Montroll,et al.  Anomalous transit-time dispersion in amorphous solids , 1975 .

[11]  N. Tessler,et al.  Carrier heating in disordered organic semiconductors , 2006 .

[12]  I. P. Zvyagin,et al.  Percolation Approach to Hopping Transport in Organic Disordered Solids , 2002 .

[13]  H. Bässler,et al.  Disorder in Charge Transport in Doped Polymers , 1994 .

[14]  Paul Heremans,et al.  Charge carrier mobility in doped semiconducting polymers , 2003 .

[15]  C. M. Elliott,et al.  Organic homojunction diodes with a high built-in potential: interpretation of the current-voltage characteristics by a generalized Einstein relation. , 2005, Physical review letters.

[16]  Effective-medium theory of hopping charge-carrier transport in weakly disordered organic solids , 2002 .

[17]  M. Abkowitz,et al.  Hopping transport in prototypical organic glasses , 1982 .

[18]  R. Schmechel.  Hopping transport in doped organic semiconductors: A theoretical approach and its application to p-doped zinc-phthalocyanine , 2003 .

[19]  E. I. Levin,et al.  Hopping Photoconductivity in Amorphous Semiconductors: Dependence on Temperature, Electric Field and Frequency , 1990 .

[20]  W. D. Gill.  Drift mobilities in amorphous charge‐transfer complexes of trinitrofluorenone and poly‐n‐vinylcarbazole , 1972 .

[21]  N. Tessler,et al.  Current voltage relation of amorphous materials based pn diodes—the effect of degeneracy in organic polymers/molecules , 2009 .

[22]  C. Chan,et al.  Direct determination of the hole density of states in undoped and doped amorphous organic films with high lateral resolution. , 2005, Physical review letters.

[23]  U. Ravaioli,et al.  An improved energy transport model including nonparabolicity and non-Maxwellian distribution effects , 1992, IEEE Electron Device Letters.

[24]  A. Nenashev,et al.  Effect of electric field on diffusion in disordered materials. II. Two- and three-dimensional hopping transport , 2009, 0912.3169.

[25]  R. Coehoorn,et al.  Charge-carrier concentration dependence of the hopping mobility in organic materials with Gaussian disorder , 2005 .

[26]  S. D. Baranovskii,et al.  How to find out the density of states in disordered organic semiconductors. , 2012, Physical review letters.

[27]  Vinay Ambegaokar,et al.  Hopping Conductivity in Disordered Systems , 1971 .

[28]  H. Bässler,et al.  How do Triplets and Charges Move in Disordered Organic Semiconductors? A Monte Carlo Study Comprising the Equilibrium and Nonequilibrium Regime , 2012 .

[29]  Nir Tessler,et al.  Generalized Einstein relation for disordered semiconductors—implications for device performance , 2002 .

[30]  Richard L. Martin,et al.  Molecular geometry fluctuations and field-dependent mobility in conjugated polymers , 2001 .

[31]  P. Blom,et al.  Unified description of charge-carrier mobilities in disordered semiconducting polymers. , 2005, Physical review letters.