Determination of gap defect states in organic bulk heterojunction solar cells from capacitance measurements

Energy distributions density-of-states DOS of defects in the effective band gap of organic bulk heterojunctions are determined by means of capacitance methods. The technique consists of calculating the junction capacitance derivative with respect to the angular frequency of the small voltage perturbation applied to thin film poly3-hexylthiopheneP3HT6,6-phenyl C61-butyric acid methyl ester PCBM solar cells. The analysis, which was performed on blends of different composition, reveals the presence of defect bands exhibiting Gaussian shape located at E 0.38 eV above the highest occupied molecular orbital level of the P3HT. The disorder parameter , which accounts for the broadening of the Gaussian DOS, lies within the range of 49‐66 meV. The total density of defects results of order 10 16 cm 3 .© 2009 American Institute of Physics.

[1]  Steven S. Hegedus,et al.  Thin‐film solar cells: device measurements and analysis , 2004 .

[2]  Juan Bisquert,et al.  Simultaneous determination of carrier lifetime and electron density-of-states in P3HT:PCBM organic solar cells under illumination by impedance spectroscopy , 2010 .

[3]  R. Street.  Electronic Processes in Noncrystalline Materials , 1973 .

[4]  S. Hegedus,et al.  Midgap states in a‐Si:H and a‐SiGe:H p‐i‐n solar cells and Schottky junctions by capacitance techniques , 1992 .

[5]  J. Bisquert,et al.  Relaxation of photogenerated carriers in P3HT:PCBM organic blends. , 2009, ChemSusChem.

[6]  Christoph J. Brabec,et al.  Charge recombination in conjugated polymer/fullerene blended films studied by transient absorption spectroscopy , 2003 .

[7]  Jef Poortmans,et al.  Thin Film Solar Cells: Fabrication, Characterization and Applications , 2006 .

[8]  Toshihide Kamata,et al.  Influence of moisture on device characteristics of polythiophene-based field-effect transistors , 2004 .

[9]  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.

[10]  Xiong Gong,et al.  Thermally Stable, Efficient Polymer Solar Cells with Nanoscale Control of the Interpenetrating Network Morphology , 2005 .

[11]  L. De Schepper,et al.  Observation of the subgap optical absorption in polymer-fullerene blend solar cells , 2006 .

[12]  J. Bisquert,et al.  Band unpinning and photovoltaic model for P3HT:PCBM organic bulk heterojunctions under illumination , 2008 .

[13]  J. Bisquert,et al.  Effects of the Gaussian energy dispersion on the statistics of polarons and bipolarons in conducting polymers. , 2004, The Journal of chemical physics.

[14]  R. Herberholz,et al.  Determination of defect distributions from admittance measurements and application to Cu(In,Ga)Se2 based heterojunctions , 1996 .

[15]  S. Bauer,et al.  Unusual electromechanical effects in organic semiconductor Schottky contacts: Between piezoelectricity and electrostriction , 2005 .

[16]  Steven Holdcroft,et al.  INTERACTION OF OXYGEN WITH CONJUGATED POLYMERS : CHARGE TRANSFER COMPLEX FORMATION WITH POLY(3-ALKYLTHIOPHENES) , 1997 .

[17]  I. Balberg.  Relation between distribution of states and the space‐charge‐region capacitance in semiconductors , 1985 .

[18]  Juan Bisquert,et al.  Charge carrier mobility and lifetime of organic bulk heterojunctions analyzed by impedance spectroscopy , 2008 .

[19]  Nelson E. Coates,et al.  Bulk heterojunction solar cells with internal quantum efficiency approaching 100 , 2009 .

[20]  T. Nguyen,et al.  Defects in organic electronic devices , 2008 .

[21]  J. Nelson.  The physics of solar cells , 2003 .

[22]  B. Huisman,et al.  Photoimpedance spectroscopy of poly(3-hexyl thiophene) metal-insulator-semiconductor diodes , 2003 .

[23]  Lionel C. Kimerling,et al.  Influence of deep traps on the measurement of free‐carrier distributions in semiconductors by junction capacitance techniques , 1974 .

[24]  Arun Madan,et al.  The Physics and Applications of Amorphous Semiconductors , 1988 .

[25]  A. Aberle.  Thin-film solar cells , 2009 .