Influence of Solvent Mixing on the Morphology and Performance of Solar Cells Based on Polyfluorene Copolymer/Fullerene Blends

The influence of the solvent on the morphology and performance of polymer solar cells is investigated in devices based on blends of the polyfluorene copolymer, poly(2,7‐(9,9‐dioctyl‐fluorene)‐alt‐5,5‐(4′,7′‐di‐2‐thienyl‐2′,1′,3′‐benzothiadiazole)), and [6,6]‐phenyl‐C61‐butyric acid methyl ester. The blends are spin‐coated from chloroform or from chloroform mixed with small amounts of xylene, toluene, or chlorobenzene. The devices are characterized under monochromatic light and solar illumination AM1.5 (AM: air mass). An enhancement of the photocurrent density is observed in diodes made from chloroform mixed with chlorobenzene, and reduced photocurrent density is observed in diodes made from chloroform mixed with xylene or toluene, compared to diodes made from neat chloroform. The open‐circuit voltages are almost the same in all diodes. The surfaces of the active layers are imaged using atomic force microscopy. Height images indicate that a finer and more uniform distribution of domains corresponds to the diodes with enhanced photocurrent that are made from chloroform mixed with chlorobenzene, while a structure with larger domains is associated with the lower photocurrents in the diodes made from chloroform mixed with xylene or toluene. The influence of the morphology on the excited‐state dynamics and charge generation is investigated using time‐resolved spectroscopy. Fast formation of bound charge pairs followed by their conversion into free charge carriers is resolved, and excitation‐intensity‐dependent non‐geminate recombination of free charges is observed. A significant enhancement in free‐charge‐carrier generation is observed on introducing chlorobenzene into chloroform. Imaging photocurrent generation from the solar cells with a light‐pulse technique shows an inhomogeneous photocurrent distribution, which is related to the undulations in the thickness of the active layer. Thicker parts of the diodes yield higher photocurrent values.

[1]  E. Moons,et al.  Control of phase separation in blends of polyfluorene (co)polymers and C60-derivative PCBM , 2005 .

[2]  Donal D. C. Bradley,et al.  Device annealing effect in organic solar cells with blends of regioregular poly(3-hexylthiophene) and soluble fullerene , 2005 .

[3]  O. Inganäs,et al.  Optical optimization of polyfluorene-fullerene blend photodiodes , 2005 .

[4]  Dieter Meissner,et al.  Nanoscale Morphology of Conjugated Polymer/Fullerene‐Based Bulk‐ Heterojunction Solar Cells , 2004 .

[5]  Christoph J. Brabec,et al.  Organic photovoltaics: technology and market , 2004 .

[6]  O. Inganäs,et al.  Optical modelling of a layered photovoltaic device with a polyfluorene derivative/fullerene as the active layer , 2004 .

[7]  Mats Andersson,et al.  Low bandgap alternating polyfluorene copolymers in plastic photodiodes and solar cells , 2004 .

[8]  Xiaoniu Yang,et al.  Relating the Morphology of Poly(p‐phenylene vinylene)/Methanofullerene Blends to Solar‐Cell Performance , 2004 .

[9]  J. Hummelen,et al.  Morphology and fluorescence quenching in photovoltaic samples containing fullerene and poly(p-phenylene-vinylene) derivatives , 2004 .

[10]  R. Friend,et al.  Morphological dependence of charge generation and transport in blended polyfluorene photovoltaic devices , 2004 .

[11]  J. Hummelen,et al.  Polyfluorene copolymer based bulk heterojunction solar cells , 2004 .

[12]  P. C. Chui,et al.  Influence of solvent on film morphology and device performance of poly(3-hexylthiophene):TiO2 nanocomposite solar cells , 2004 .

[13]  V. Mihailetchi,et al.  Cathode dependence of the open-circuit voltage of polymer:fullerene bulk heterojunction solar cells , 2003 .

[14]  Mats Andersson,et al.  High‐Performance Polymer Solar Cells of an Alternating Polyfluorene Copolymer and a Fullerene Derivative , 2003 .

[15]  V. Sundström,et al.  Ultrafast Excitation Transfer and Trapping in a Thin Polymer Film. , 2003 .

[16]  Brian A. Gregg,et al.  Excitonic Solar Cells , 2003 .

[17]  Niyazi Serdar Sariciftci,et al.  Effects of Postproduction Treatment on Plastic Solar Cells , 2003 .

[18]  Giovanni Ridolfi,et al.  The Effect of a Mild Thermal Treatment on the Performance of Poly(3‐alkylthiophene)/Fullerene Solar Cells , 2002 .

[19]  Richard H. Friend,et al.  The origin of the open-circuit voltage in polyfluorene-based photovoltaic devices , 2002 .

[20]  Klaus Meerholz,et al.  Influence of the anodic work function on the performance of organic solar cells. , 2002, Chemphyschem : a European journal of chemical physics and physical chemistry.

[21]  Christoph J. Brabec,et al.  The influence of materials work function on the open circuit voltage of plastic solar cells , 2002 .

[22]  Mm Martijn Wienk,et al.  Accurate efficiency determination and stability studies of conjugated polymer/fullerene solar cells , 2002 .

[23]  C. Brabec,et al.  Origin of the Open Circuit Voltage of Plastic Solar Cells , 2001 .

[24]  Christoph J. Brabec,et al.  Tracing photoinduced electron transfer process in conjugated polymer/fullerene bulk heterojunctions in real time , 2001 .

[25]  D. Birnie.  Rational solvent selection strategies to combat striation formation during spin coating of thin films , 2001 .

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

[27]  Mats Andersson,et al.  University of Groningen Polymer photovoltaic devices from stratified multilayers of donor-acceptor blends , 2022 .

[28]  Mats Andersson,et al.  Laminated fabrication of polymeric photovoltaic diodes , 1998, Nature.

[29]  U. Steiner,et al.  Structure formation via polymer demixing in spin-cast films , 1997 .

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

[31]  D. Meyerhofer.  Characteristics of resist films produced by spinning , 1978 .