Study of Optical Properties and Molecular Aggregation of Conjugated Low Band Gap Copolymers: PTB7 and PTB7-Th

A comparative study of the optical properties of two well-known copolymers for photovoltaic applications, the PTB7 and the PTB7-Th, is presented. This study contributes to the understanding of the photophysics and permits correlation of the morphological change to the optical properties. For this purpose, Variable Angle Spectroscopic Ellipsometry (VASE) measurements are performed to determine the optical transitions as well as the band gap of PTB7 and PTB7-Th thin films from the imaginary parts of the dielectric functions. Then, the molecular aggregations in chlorobenzene solutions are investigated by means of absorbance and photoluminescence measurements as a function of concentration and temperature. These solution measurements are compared to film measurements in order to isolate interchain and intrachain optical transitions.

[1]  S. Chen,et al.  A Review on the Emitting Species in Conjugated Polymers for Photo‐ and Electro‐luminescence , 2010 .

[2]  Fujun Zhang,et al.  Energy level alignment and morphology of interfaces between molecular and polymeric organic semiconductors , 2007 .

[3]  Yu-Shan Cheng,et al.  Single Junction Inverted Polymer Solar Cell Reaching Power Conversion Efficiency 10.31% by Employing Dual-Doped Zinc Oxide Nano-Film as Cathode Interlayer , 2014, Scientific Reports.

[4]  Yu-Shan Cheng,et al.  Fullerene Derivative‐Doped Zinc Oxide Nanofilm as the Cathode of Inverted Polymer Solar Cells with Low‐Bandgap Polymer (PTB7‐Th) for High Performance , 2013, Advanced materials.

[5]  M. Jayakannan,et al.  Probing the pi-stacking induced molecular aggregation in pi-conjugated polymers, oligomers, and their blends of p-phenylenevinylenes. , 2008, The journal of physical chemistry. B.

[6]  Jenny Clark,et al.  Role of intermolecular coupling in the photophysics of disordered organic semiconductors: aggregate emission in regioregular polythiophene. , 2007, Physical review letters.

[7]  Benjamin J. Schwartz,et al.  Conjugated polymer aggregates in solution: Control of interchain interactions , 1999 .

[8]  Carlos Silva,et al.  H- and J-aggregate behavior in polymeric semiconductors. , 2014, Annual review of physical chemistry.

[9]  F. Spano,et al.  Interplay between intrachain and interchain interactions in semiconducting polymer assemblies: the HJ-aggregate model. , 2012, The Journal of chemical physics.

[10]  Mario Leclerc,et al.  A Low‐Bandgap Poly(2,7‐Carbazole) Derivative for Use in High‐Performance Solar Cells , 2007 .

[11]  Yang Yang,et al.  Manipulating regioregular poly(3-hexylthiophene) : [6,6]-phenyl-C61-butyric acid methyl ester blends—route towards high efficiency polymer solar cells , 2007 .

[12]  Ludovic Escoubas,et al.  Optical performance and color investigations of hybrid solar cells based on P3HT:ZnO, PCPDTBT:ZnO, PTB7:ZnO and DTS(PTTh2)2:ZnO , 2014 .

[13]  Luping Yu,et al.  A new class of semiconducting polymers for bulk heterojunction solar cells with exceptionally high performance. , 2010, Accounts of chemical research.

[14]  Miao Xu,et al.  Enhanced power-conversion efficiency in polymer solar cells using an inverted device structure , 2012, Nature Photonics.

[15]  Yang Yang,et al.  A polymer tandem solar cell with 10.6% power conversion efficiency , 2013, Nature Communications.

[16]  Yang Yang,et al.  Silicon Atom Substitution Enhances Interchain Packing in a Thiophene‐Based Polymer System , 2010, Advanced materials.

[17]  T. Xu,et al.  Solution Phase Exciton Diffusion Dynamics of a Charge-Transfer Copolymer PTB7 and a Homopolymer P3HT. , 2015, The journal of physical chemistry. B.

[18]  M. Kasha,et al.  The exciton model in molecular spectroscopy , 1965 .

[19]  Jianhui Hou,et al.  Design, Application, and Morphology Study of a New Photovoltaic Polymer with Strong Aggregation in Solution State , 2012 .

[20]  Junbiao Peng,et al.  Low Band‐Gap Conjugated Polymers with Strong Interchain Aggregation and Very High Hole Mobility Towards Highly Efficient Thick‐Film Polymer Solar Cells , 2014, Advanced materials.

[21]  Juan Bisquert,et al.  Interplay of Optical, Morphological, and Electronic Effects of ZnO Optical Spacers in Highly Efficient Polymer Solar Cells , 2014 .

[22]  Jenny Nelson,et al.  Morphology evolution via self-organization and lateral and vertical diffusion in polymer:fullerene solar cell blends. , 2008, Nature materials.

[23]  F. Spano.  The spectral signatures of Frenkel polarons in H- and J-aggregates. , 2010, Accounts of chemical research.

[24]  Jean Roncali,et al.  Molecular Engineering of the Band Gap of π-Conjugated Systems: Facing Technological Applications , 2007 .

[25]  Ludovic Escoubas,et al.  Ellipsometric study of the optical transitions of PC60BM and PC70BM thin films , 2015 .

[26]  A. Heeger,et al.  Ultrafast Relaxation of the Poly(3-hexylthiophene) Emission Spectrum , 2011 .

[27]  Jenny Clark,et al.  Determining exciton bandwidth and film microstructure in polythiophene films using linear absorption spectroscopy , 2009, 0903.1670.

[28]  Luping Yu,et al.  Examining the effect of the dipole moment on charge separation in donor-acceptor polymers for organic photovoltaic applications. , 2011, Journal of the American Chemical Society.