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Title: Morphological Characterization of a Low-Bandgap Crystalline Polymer: PCBM Bulk Heterojunction Solar Cells

Understanding the morphology of polymer-based bulk heterojunction (BHJ) solar cells is necessary to improve device efficiencies. Blends of a low-bandgap silole-containing conjugated polymer, poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b;2',3'-d]silole)-2,6-diyl-alt-(4,7-bis(2-thienyl)-2,1,3-benzothiadiazole)-5,5'-diyl] (PSBTBT) with [6,6]phenyl-C61-butyric acid methyl ester (PCBM) were investigated under different processing conditions. The surface morphologies and vertical segregation of the “As-Spun”, “Pre-Annealed”, and “Post-Annealed” films were studied by scanning force microscopy, contact angle measurements, X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure spectroscopy, dynamic secondary ion mass spectrometry, and neutron reflectivity. The results showed that PSBTBT was enriched at the cathode interface in the “As-Spun” films and thermal annealing increased the segregation of PSBTBT to the free surface, while thermal annealing after deposition of the cathode increased the PCBM concentration at the cathode interface. Grazing-incidence X-ray diffraction and small-angle neutron scattering showed that the crystallization of PSBTBT and segregation of PCBM occurred during spin coating, and thermal annealing increased the ordering of PSBTBT and enhanced the segregation of the PCBM, forming domains ~10 nm in size, leading to an improvement in photovoltaic performance.
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Publication Date:
OSTI Identifier:
DOE Contract Number:
Resource Type:
Journal Article
Resource Relation:
Journal Name: Advanced Energy Materials; Journal Volume: 1(5); Journal Issue: 5; Related Information: PHaSE partners with University of Massachusetts, Amherst (lead) and Lowell; Oak Ridge National Laboratory; Pennsylvania State University; Renssalaer Polytechnic Institute; University of Pittsburgh
Research Org:
Energy Frontier Research Centers (EFRC); Polymer-Based Materials for Harvesting Solar Energy (PHaSE)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
14 SOLAR ENERGY; solar (photovoltaic), charge transport, materials and chemistry by design, synthesis (novel materials), synthesis (self-assembly)