Efficient, ordered bulk heterojunction nanocrystalline solar cells by annealing of ultrathin squaraine thin films

Guodan Wei, Richard R. Lunt, Kai Sun, Siyi Wang, Mark E. Thompson, Stephen R. Forrest

Research output: Research - peer-reviewArticle

  • 108 Citations

Abstract

Spin-cast 2,4-bis[4-(N,N-diisobutylamino)-2,6-dihydroxyphenyl]squaraine (SQ) thin films only 62 Å thick are converted from amorphous to polycrystalline via postannealing at elevated temperatures. The surface roughness of the SQ films increases by a factor of 2, while selected area electron diffraction spectra indicate an increase in the extent of postannealed film crystallinity. Dichloromethane solvent annealing is also demonstrated to increase the exciton diffusion length of SQ by a factor of 3 over thermally annealed SQ films as a result of further enhancement in crystalline order. We find that the roughened surface features have a length scale on the order of the exciton diffusion length. Hence, coating the donor SQ with the acceptor, C 60, results in a nearly optimum controlled bulk heterojunction solar cell structure. Optimized SQ/C60 photovoltaic cells have a power conversion efficiency of ηp = 4.6 ± 0.1% (correcting for solar mismatch) at 1 sun (AM1.5G) simulated solar intensity, and a corresponding peak external quantum efficiency of EQE = 43 ± 1% even for the very thin SQ layers employed.

LanguageEnglish (US)
Pages3555-3559
Number of pages5
JournalNano Letters
Volume10
Issue number9
DOIs
StatePublished - Sep 8 2010
Externally publishedYes

Profile

Ultrathin films
Heterojunctions
Solar cells
Annealing
Thin films
squaraine
heterojunctions
solar cells
annealing
thin films
LDS 751
Excitons
diffusion length
excitons
Photovoltaic cells
Methylene Chloride
Quantum efficiency
Electron diffraction
Sun
Conversion efficiency

Keywords

  • bulk heterojunction
  • exciton
  • Photovoltaic
  • vacuum deposition

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Bioengineering
  • Chemistry(all)
  • Materials Science(all)
  • Mechanical Engineering

Cite this

Efficient, ordered bulk heterojunction nanocrystalline solar cells by annealing of ultrathin squaraine thin films. / Wei, Guodan; Lunt, Richard R.; Sun, Kai; Wang, Siyi; Thompson, Mark E.; Forrest, Stephen R.

In: Nano Letters, Vol. 10, No. 9, 08.09.2010, p. 3555-3559.

Research output: Research - peer-reviewArticle

Wei, Guodan ; Lunt, Richard R. ; Sun, Kai ; Wang, Siyi ; Thompson, Mark E. ; Forrest, Stephen R./ Efficient, ordered bulk heterojunction nanocrystalline solar cells by annealing of ultrathin squaraine thin films. In: Nano Letters. 2010 ; Vol. 10, No. 9. pp. 3555-3559
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