Energy-level alignment at organic heterointerfaces

Quantitative modeling demystifies the complex and diverse energetics observed at interfaces between organic semiconductors. Today’s champion organic (opto-)electronic devices comprise an ever-increasing number of different organic-semiconductor layers. The functionality of these complex heterostructures largely derives from the relative alignment of the frontier molecular-orbital energies in each layer with respect to those in all others. Despite the technological relevance of the energy-level alignment at organic heterointerfaces, and despite continued scientific interest, a reliable model that can quantitatively predict the full range of phenomena observed at such interfaces is notably absent. We identify the limitations of previous attempts to formulate such a model and highlight inconsistencies in the interpretation of the experimental data they were based on. We then develop a theoretical framework, which we demonstrate to accurately reproduce experiment. Applying this theory, a comprehensive overview of all possible energy-level alignment scenarios that can be encountered at organic heterojunctions is finally given. These results will help focus future efforts on developing functional organic interfaces for superior device performance.

[1]  C Zannoni,et al.  Exploring the energy landscape of the charge transport levels in organic semiconductors at the molecular scale. , 2013, Accounts of chemical research.

[2]  Andrew T. S. Wee,et al.  Origin of the energy level alignment at organic/organic interfaces: The role of structural defects , 2014 .

[3]  C. Medaglia,et al.  A Numerical Study , 2005 .

[4]  David Beljonne,et al.  Electronic Structure and Geminate Pair Energetics at Organic–Organic Interfaces: The Case of Pentacene/C60 Heterojunctions , 2009 .

[5]  W. R. Salaneck,et al.  Electroluminescence in conjugated polymers , 1999, Nature.

[6]  Yongli Gao,et al.  Surface analytical studies of interfaces in organic semiconductor devices , 2010 .

[7]  David Beljonne,et al.  Energetics of Electron–Hole Separation at P3HT/PCBM Heterojunctions , 2013 .

[8]  Norbert Koch,et al.  Organic electronic devices and their functional interfaces. , 2007, Chemphyschem : a European journal of chemical physics and physical chemistry.

[9]  Wei Zhao,et al.  Substrate-dependent electronic structure of an organic heterojunction , 2008 .

[10]  R. Johnsen,et al.  Theory and Experiment , 2010 .

[11]  Chun-Sing Lee,et al.  Substrate effects on the electronic properties of an organic/organic heterojunction , 2006 .

[12]  Shu Zhong,et al.  The role of gap states in the energy level alignment at the organic-organic heterojunction interfaces. , 2012, Physical chemistry chemical physics : PCCP.

[13]  David Beljonne,et al.  Electronic Structure and Geminate Pair Energetics at Organic–Organic Interfaces: The Case of Pentacene/C60 Heterojunctions , 2009 .

[14]  Weiying Gao,et al.  Energy level alignment at organic heterojunctions : Role of the charge neutrality level , 2005 .

[15]  Norbert Koch,et al.  Fermi level pinning induced electrostatic fields and band bending at organic heterojunctions , 2014 .

[16]  Richard Murdey,et al.  Quantitatively identical orientation-dependent ionization energy and electron affinity of diindenoperylene , 2013 .

[17]  K. Knapp,et al.  Empirical investigation of the energy payback time for photovoltaic modules , 2002 .

[18]  Norbert Koch,et al.  The Impact of Disorder on the Energy Level Alignment at Molecular Donor–Acceptor Interfaces , 2015 .

[19]  Xiaoyang Zhu,et al.  Understanding the Interface Dipole of Copper Phthalocyanine (CuPc)/C60: Theory and Experiment. , 2012, The journal of physical chemistry letters.

[20]  H. Bässler.  Charge Transport in Disordered Organic Photoconductors a Monte Carlo Simulation Study , 1993 .

[21]  Denis Andrienko,et al.  Modeling of organic light emitting diodes: From molecular to device properties , 2015, International Conference on Numerical Simulation of Optoelectronic Devices.

[22]  William R. Salaneck,et al.  Formation of the Interfacial Dipole at Organic‐Organic Interfaces: C60/Polymer Interfaces , 2007 .

[23]  R. Meyer,et al.  A comparative density functional theory study of the direct synthesis of H2O2 on Pd, Pt and Au surfaces , 2011 .

[24]  F. Flores,et al.  The role of charge transfer in the energy level alignment at the pentacene/C60 interface. , 2014, Physical chemistry chemical physics : PCCP.

[25]  Davide Bartesaghi,et al.  The Effect of Large Compositional Inhomogeneities on the Performance of Organic Solar Cells: A Numerical Study , 2015 .

[26]  Shane R. Yost,et al.  Electrostatic Effects at Organic Semiconductor Interfaces: A Mechanism for “Cold” Exciton Breakup , 2013 .

[27]  C. Tang.  Two‐layer organic photovoltaic cell , 1986 .

[28]  Chun-Sing Lee,et al.  Electronic structures of organic/organic heterojunctions: From vacuum level alignment to Fermi level pinning , 2007 .

[29]  Fernando Flores,et al.  Induced Density of States model for weakly-interacting organic semiconductor interfaces , 2007 .

[30]  Donghang Yan,et al.  Interfacial electronic structure of copper hexadecafluorophthalocyanine and phthalocyanatotin (IV) dichloride studied by photoemission spectroscopy , 2010 .

[31]  James C. Blakesley,et al.  Relationship between energetic disorder and open-circuit voltage in bulk heterojunction organic solar cells , 2011 .

[32]  C. Tang,et al.  Organic Electroluminescent Diodes , 1987 .

[33]  Helmut Dosch,et al.  Experimental relation between Stranski-Krastanov growth of DIP/F16CoPc heterostructures and the reconstruction of the organic interface , 2009 .

[34]  Karl Leo,et al.  Molecular-scale simulation of electroluminescence in a multilayer white organic light-emitting diode. , 2013, Nature materials.

[35]  Donghang Yan,et al.  Organic heterostructures in organic field-effect transistors , 2010 .

[36]  Tetsuo Tsutsui,et al.  Organic electroluminescent device having a hole conductor as an emitting layer , 1989 .

[37]  Norbert Koch,et al.  Band‐Bending in Organic Semiconductors: the Role of Alkali‐Halide Interlayers , 2014, Advanced materials.

[38]  Stephen J. Fonash,et al.  Computer simulation of actual and Kelvin‐probe‐measured potential profiles: Application to amorphous films , 1990 .

[39]  Hironori Kaji,et al.  Refined Structure Determination of Blue-Emitting Tris(8-hydroxyquinoline) Aluminum(III) (Alq3) by the Combined Use of Cross-Polarization/Magic-Angle Spinning 13C Solid-State NMR and First-Principles Calculation , 2013 .

[40]  Zheng-Hong Lu,et al.  Universal energy-level alignment of molecules on metal oxides. , 2011, Nature materials.

[41]  Donghang Yan,et al.  Electronic structure of interfaces between copper-hexadecafluoro-phthalocyanine and 2,5-bis(4-biphenylyl) bithiophene , 2007 .

[42]  Hiroyuki Yoshida,et al.  Near-ultraviolet inverse photoemission spectroscopy using ultra-low energy electrons , 2012 .

[43]  A. C. Albrecht,et al.  Chlorophyll-a photovoltaic cells , 1975, Nature.

[44]  Princeton University,et al.  Dipole formation at metal/PTCDA interfaces: Role of the Charge Neutrality Level , 2004 .

[45]  Raj René Janssen,et al.  Kinetic Monte Carlo Study of the Sensitivity of OLED Efficiency and Lifetime to Materials Parameters , 2015 .

[46]  Manousakis.  Electronic structure of C60 within the tight-binding approximation. , 1991, Physical review. B, Condensed matter.

[47]  Karin Zojer,et al.  Impact of energy alignment and morphology on the efficiency in inorganic–organic hybrid solar cells , 2010 .

[48]  R. Fleming,et al.  Deposition and characterization of fullerene films , 1991 .

[49]  Geoffrey R. Hutchison,et al.  Effects of Delocalized Charge Carriers in Organic Solar Cells: Predicting Nanoscale Device Performance from Morphology , 2015 .

[50]  P. Magnante,et al.  Electroluminescence in Organic Crystals , 1963 .

[51]  Mats Fahlman,et al.  Charge equilibration and potential steps in organic semiconductor multilayers , 2012 .

[52]  R. Holmes,et al.  Tailored exciton diffusion in organic photovoltaic cells for enhanced power conversion efficiency. , 2013, Nature materials.

[53]  K. Knapp,et al.  Empirical investigation of the energy payback time for photovoltaic modules , 2001 .

[54]  Wei Chen,et al.  Organic–Organic Heterojunction Interfaces: Effect of Molecular Orientation , 2011 .

[55]  Heinz von Seggern,et al.  Pitfalls in Kelvin probe measurements , 2009 .

[56]  Markus Hösel,et al.  Solar cells with one-day energy payback for the factories of the future , 2012 .

[57]  Gregor Schwartz,et al.  Efficient Organic Tandem Solar Cells based on Small Molecules , 2011 .

[58]  David Beljonne,et al.  Interfacial dipole and band bending in model pentacene/C60 heterojunctions , 2013 .

[59]  William R. Salaneck,et al.  Influence of the electrode work function on the energy level alignment at organic-organic interfaces , 2007 .

[60]  Jun Wang,et al.  Organic heterojunction and its application for double channel field-effect transistors , 2005 .

[61]  Katherine A Mazzio,et al.  The future of organic photovoltaics. , 2015, Chemical Society reviews.

[62]  O. V. Molodtsova,et al.  Electronic properties of the organic semiconductor interfaces CuPc∕C60 and C60∕CuPc , 2006 .

[63]  Norbert Koch,et al.  Organic semiconductor density of states controls the energy level alignment at electrode interfaces , 2014, Nature Communications.

[64]  Oded Hod,et al.  Electronic structure of copper phthalocyanine: a comparative density functional theory study. , 2008, The Journal of chemical physics.

[65]  D. Batens,et al.  Theory and Experiment , 1988 .

[66]  W. A. Dench,et al.  Quantitative electron spectroscopy of surfaces: A standard data base for electron inelastic mean free paths in solids , 1979 .

[67]  Antoine Kahn,et al.  Effect of electrical doping on molecular level alignment at organic–organic heterojunctions , 2003 .

[68]  James C. Blakesley,et al.  Charge transfer at polymer-electrode interfaces: The effect of energetic disorder and thermal injection on band bending and open-circuit voltage , 2009 .

[69]  Karl Leo,et al.  Impact of mesoscale order on open-circuit voltage in organic solar cells. , 2015, Nature materials.

[70]  Karin Zojer,et al.  Influence of morphology and polymer:nanoparticle ratio on device performance of hybrid solar cells—an approach in experiment and simulation , 2013, Nanotechnology.

[71]  Wei Chen,et al.  Effect of Gap States on the Orientation-Dependent Energy Level Alignment at the DIP/F16CuPc Donor–Acceptor Heterojunction Interfaces , 2011 .