Effect of thermal annealing on exciton diffusion in a diketopyrrolopyrrole derivative.

We show that the method we have developed for measuring the singlet exciton diffusion length in blends with [6,6]-phenyl-C(61)-butyric acid methyl ester (PCBM) can be applied not only to polymeric materials, but also to small molecule organic semiconductors. Small organic molecules have a large potential for molecular re-organization upon thermal annealing. Here we show that the exciton diffusion length is decreased upon annealing from 9 to 3 nm in a thin film of a diketopyrrolopyrrole derivative. Such a variation is attributed to exciton delocalization effects in the crystalline domains that are formed during the annealing process as well as to the exciton quenching at grain boundaries.

[1]  Yang Yang,et al.  Spin‐Coated Small Molecules for High Performance Solar Cells , 2011 .

[2]  Jan Genoe,et al.  Solar cells utilizing small molecular weight organic semiconductors , 2007 .

[3]  Stephen R. Forrest,et al.  Small molecular weight organic thin-film photodetectors and solar cells , 2003 .

[4]  C. Brabec,et al.  Nanomorphology and Charge Generation in Bulk Heterojunctions Based on Low‐Bandgap Dithiophene Polymers with Different Bridging Atoms , 2010 .

[5]  Jianguo Tian,et al.  High‐Performance Solar Cells using a Solution‐Processed Small Molecule Containing Benzodithiophene Unit , 2011, Advanced materials.

[6]  C. Brabec,et al.  2.5% efficient organic plastic solar cells , 2001 .

[7]  Stephen R. Forrest,et al.  Excitons in crystalline thin films of 3,4,9,10-perylenetetracarboxylic dianhydride studied by photocurrent response , 1995 .

[8]  J. Hummelen,et al.  Polymer Photovoltaic Cells: Enhanced Efficiencies via a Network of Internal Donor-Acceptor Heterojunctions , 1995, Science.

[9]  Mauro Morana,et al.  Exciton diffusion length in narrow bandgap polymers , 2012 .

[10]  Thuc‐Quyen Nguyen,et al.  A Systematic Approach to Solvent Selection Based on Cohesive Energy Densities in a Molecular Bulk Heterojunction System , 2011 .

[11]  Wei Lin Leong,et al.  Solution-processed small-molecule solar cells with 6.7% efficiency. , 2011, Nature materials.

[12]  Hong-Bo Sun,et al.  Exciton diffusion and charge transfer dynamics in nano phase-separated P3HT/PCBM blend films. , 2011, Nanoscale.

[13]  L. Feldman,et al.  Observation of long-range exciton diffusion in highly ordered organic semiconductors. , 2010, Nature materials.

[14]  W. Graupner,et al.  Ultrafast formation of nonemissive species via intermolecular interaction in single crystals of conjugated molecules. , 2001, Physical review letters.

[15]  T. Savenije,et al.  Singlet and Triplet Exciton Diffusion in a Self‐Organizing Porphyrin Antenna Layer , 2004 .

[16]  Peter Peumans,et al.  Effect of molecular packing on the exciton diffusion length in organic solar cells , 2007 .

[17]  Xiaojing Zhou,et al.  Exciton transport in organic semiconductors: Förster resonance energy transfer compared with a simple random walk , 2012 .

[18]  C. Adachi,et al.  Small molecular organic photovoltaic cells with exciton blocking layer at anode interface for improved device performance , 2011 .

[19]  Thuc‐Quyen Nguyen,et al.  A low band gap, solution processable oligothiophene with a dialkylated diketopyrrolopyrrole chromophore for use in bulk heterojunction solar cells , 2009 .

[20]  Thuc-Quyen Nguyen,et al.  Small Molecule Solution-Processed Bulk Heterojunction Solar Cells† , 2011 .

[21]  Thuc‐Quyen Nguyen,et al.  A Low Band Gap, Solution Processable Oligothiophene with a Diketopyrrolopyrrole Core for Use in Organic Solar Cells , 2008 .

[22]  F. Würthner,et al.  One-dimensional exciton diffusion in perylene bisimide aggregates. , 2011, The journal of physical chemistry. A.

[23]  John E. Anthony,et al.  Soluble n-type pentacene derivatives as novel acceptors for organic solar cells , 2009 .

[24]  David L. Carroll,et al.  High-efficiency photovoltaic devices based on annealed poly(3-hexylthiophene) and 1-(3-methoxycarbonyl)-propyl-1- phenyl-(6,6)C61 blends , 2005 .

[25]  Chihaya Adachi,et al.  Correlation of hole mobility, exciton diffusion length, and solar cell characteristics in phthalocyanine/fullerene organic solar cells , 2007 .

[26]  Kai Sun,et al.  Solvent‐Annealed Crystalline Squaraine: PC70BM (1:6) Solar Cells , 2011 .

[27]  Takuji Nishimura,et al.  Mersenne twister: a 623-dimensionally equidistributed uniform pseudo-random number generator , 1998, TOMC.

[28]  Thuc-Quyen Nguyen,et al.  Nanoscale Phase Separation and High Photovoltaic Efficiency in Solution‐Processed, Small‐Molecule Bulk Heterojunction Solar Cells , 2009 .

[29]  S. Forrest,et al.  Efficient, ordered bulk heterojunction nanocrystalline solar cells by annealing of ultrathin squaraine thin films. , 2010, Nano letters.

[30]  Richard D. Schaller,et al.  Near-Field Scanning Optical Microscopy (NSOM) Studies of the Relationship between Interchain Interactions, Morphology, Photodamage, and Energy Transport in Conjugated Polymer Films , 2001 .

[31]  Martin A. Green,et al.  Solar cell efficiency tables (version 39) , 2012 .

[32]  Thuc‐Quyen Nguyen,et al.  Design, Synthesis, and Self-assembly of Oligothiophene Derivatives with a Diketopyrrolopyrrole Core , 2008 .

[33]  Valentin D. Mihailetchi,et al.  Charge Transport and Photocurrent Generation in Poly(3‐hexylthiophene): Methanofullerene Bulk‐Heterojunction Solar Cells , 2006 .

[34]  T. Savenije,et al.  Effects of molecular organization on exciton diffusion in thin films of bioinspired light-harvesting molecules , 2009 .

[35]  John E. Anthony,et al.  Photovoltaics from soluble small molecules , 2007 .

[36]  M. Weil,et al.  Dicyanovinyl–Substituted Oligothiophenes: Structure‐Property Relationships and Application in Vacuum‐Processed Small Molecule Organic Solar Cells , 2011 .

[37]  Hess,et al.  Photoexcitations in polythiophene at high pressure. , 1993, Physical review. B, Condensed matter.

[38]  Stephen R Forrest,et al.  Relationship between Crystalline Order and Exciton Diffusion Length in Molecular Organic Semiconductors , 2010, Advanced materials.

[39]  D. Hertel,et al.  Direct Comparison of Highly Efficient Solution‐ and Vacuum‐Processed Organic Solar Cells Based on Merocyanine Dyes , 2010, Advanced materials.

[40]  Xiaoniu Yang,et al.  Nanoscale morphology of high-performance polymer solar cells. , 2005, Nano letters.

[41]  Charles E. Swenberg,et al.  Electronic Processes in Organic Crystals and Polymers , 1999 .

[42]  Giovanni Bussi,et al.  Solid state effects on exciton states and optical properties of PPV. , 2002, Physical review letters.

[43]  P. Blom,et al.  Dynamics of exciton diffusion in poly( p -phenylene vinylene)/fullerene heterostructures , 2005 .