Systematic investigation of organic photovoltaic cell charge injection/performance modulation by dipolar organosilane interfacial layers

ACS Appl Mater Interfaces. 2013 Sep 25;5(18):9224-40. doi: 10.1021/am4030609. Epub 2013 Sep 6.

Abstract

With the goal of investigating and enhancing anode performance in bulk-heterojunction (BHJ) organic photovoltaic (OPV) cells, the glass/tin-doped indium oxide (ITO) anodes are modified with a series of robust silane-tethered bis(fluoroaryl)amines to form self-assembled interfacial layers (IFLs). The modified ITO anodes are characterized by contact angle measurements, X-ray reflectivity, ultraviolet photoelectron spectroscopy, X-ray photoelectron spectroscopy, grazing incidence X-ray diffraction, atomic force microscopy, and cyclic voltammetry. These techniques reveal the presence of hydrophobic amorphous monolayers of 6.68 to 9.76 Å thickness, and modified anode work functions ranging from 4.66 to 5.27 eV. Two series of glass/ITO/IFL/active layer/LiF/Al BHJ OPVs are fabricated with the active layer = poly(3-hexylthiophene):phenyl-C71-butyric acid methyl ester (P3HT:PC71BM) or poly[[4,8-bis[(2-ethylhexyl)oxy]benzo[1,2-b:4,5-b']dithiophene-2,6-diyl][3-fluoro-2-[(2-ethylhexyl)-carbonyl]thi-eno[3,4-b]thiophenediyl]]:phenyl-C71-butyric acid methyl ester (PTB7:PC71BM). OPV analysis under AM 1.5G conditions reveals significant performance enhancement versus unmodified glass/ITO anodes. Strong positive correlations between the electrochemically derived heterogeneous electron transport rate constants (ks) and the device open circuit voltage (Voc), short circuit current (Jsc), hence OPV power conversion efficiency (PCE), are observed for these modified anodes. Furthermore, the strong functional dependence of the device response on ks increases as greater densities of charge carriers are generated in the BHJ OPV active layer, and is attributable to enhanced anode carrier extraction in the case of high-ks IFLs.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Amines / chemistry
  • Electrodes
  • Fullerenes / chemistry
  • Glass / chemistry
  • Hydrophobic and Hydrophilic Interactions
  • Silanes / chemistry
  • Solar Energy*
  • Thiophenes / chemistry
  • Tin Compounds / chemistry

Substances

  • Amines
  • Fullerenes
  • Silanes
  • Thiophenes
  • Tin Compounds
  • poly(3-hexylthiophene)
  • indium tin oxide