Molecular doping of low-bandgap-polymer:fullerene solar cells: Effects on transport and solar cells

Ali Veysel Tunc, Antonietta De Sio, Daniel Riedel, Felix Deschler, Enrico Da Como, Juergen Parisi, Elizabeth von Hauff

Research output: Contribution to JournalArticleAcademicpeer-review

Abstract

We show how molecular doping can be implemented to improve the performance of solution processed bulk heterojunction solar cells based on a low-bandgap polymer mixed with a fullerene derivative. The molecular dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4-TCNQ) is introduced into blends of poly[2,6(4,4-bis-(2-ethylhexyl)-4H-cyclopenta[2,1-b:3,4-b0]-dithiophene)-alt-4,7-(2,1,3-benzothiadiazole)] (PCPDTBT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) via co-solution in a range of concentrations from 0% to 1%. We demonstrate that the hole conductivity and mobility increase with doping concentration using field-effect measurements. Photoinduced absorption (PIA) spectroscopy reveals that the polaron density in the blends increases with doping. We show that the open circuit voltage and short circuit current of the corresponding solar cells can be improved by doping at 0.5%, resulting in improved power conversion efficiencies. The increase in performance is discussed in terms of trap filling due to the increased carrier density, and reduced recombination correlated to the improvement in mobility.
Original languageEnglish
Pages (from-to)290-296
JournalOrganic electronics
Volume13
Issue number2
DOIs
Publication statusPublished - Feb 2012

Keywords

  • Photovoltaics
  • Organic semiconductors
  • Doping
  • Conducting polymer
  • Solar cells
  • Carrier mobility

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