Charge transfer and polaron states in bulk heterojunction solar cells

ORAL

Abstract

The absorption mechanisms in bulk heterojunction solar cells have been studied using Fourier Transform Photocurrent Spectroscopy and Electroabsorption Spectroscopy. Device structures have been fabricated by sandwiching the active films between transparent conductive (ITO) and aluminum electrodes. The active films have been spin coated using 3 types of polymers, P3HT, PCDTBT, and PCPDTBT, and PC60BM. For comparison, structures containing polymer films w/o PCBM have been prepared and studied. The presence of PCBM is known to enhance dramatically the photocurrent generation. Our measurements reveal that dramatic changes appear also in the subgap photocurrent and electroabsorption. We identify a characteristic feature just below the absorption edge as charge transfer state in agreement with previous reports. The polaron states have been identified in the electroabsorption spectra at energies coinciding with the maximum of the absorption spectrum. Impedance spectroscopy data support further this hypothesis. These results contribute to the differentiation between the charge transfer and polaron states in bulk-heterojunction structures.

–

Authors

  • Marian Tzolov

    Department of Physics, Lock Haven University, Lock Haven University of PA

  • Shahab Derakhshan

    Drexel University, Univ of Delaware, Princeton University, Naval Surface Warfare Center\Carderock Division\West Bethesda site, Naval Surface Warfare Center and Georgetown Univ., Dept. of Physics and Astronomy, University of Delaware, Dept. of Physics and Astronomy, University of Deleware, Dept. of Physics and Astronomy, University of Nevada-Reno, university of Delaware, Contributors, Department of Physics, Astronomy and Geosciences, Towson University, Choice Research Group, Univ of the Sciences in Philadephia, Rutgers Univ, National Institute of Standards and Technology, Department of Chemistry, West Chester University, West Chester, PA 19383, Bucknell University, Towson University, University of Maryland, College of William and Mary, Naval Research Laboratory, Department of Physics, Villanova University, Department of Chemistry, Faculty of Medicine, University of Brescia, Department of Chemistry, State University of New York at Potsdam, Delaware State University DE, NIH Bethesda MD, Wilmington Friends School DE, University Of Rochester NY, Delaware State University, Department of Physics and Astronomy,West Virginia University, The National Energy Technology Laboratory, Non-tenure track professor at research institution, Government Sponsored Laboratory, Research and Development at Industrial Company, Tenure-track Professor at 4 yr college, Department of Physics and Astronomy and Department of Chemistry and Biochemistry, University of Delaware, Biology and Soft Matter Division, Oak Ridge National Laboratory, and Department of Physics and Astronomy, The University of Tennessee, Biology and Soft Matter Division, Oak Ridge National Laboratory, Lehigh Univ, Johns Hopkins Univ, NIST, GMU, GWU, Lock Haven University of PA, Univ of Maryland-Balt County; Center for Nanoscale Materials, Argonne National Laboratory, Department of Chemistry, Northwestern University, Univ of Maryland-Balt County, Pennsylvania State University, BAE Systems, Inc., Nashua, New Hampshire 03061, Department of Physics, West Virginia University, Morgantown, West Virginia, 26506-6315, California State University, Long Beach