Efficient hole transport material formed by atmospheric pressure plasma functionalization of Spiro-OMeTAD

Paheli Ghosh, Aruna Ivaturi, Debabrata Bhattacharya, James Bowen, Tony Nixon, Jan Kowal , Nicholas St. J. Braithwaite, Satheesh Krishnamurthy

Research output: Contribution to journalComment/debatepeer-review

1 Citation (Scopus)

Abstract

A technique to increase the conductivity of Spiro-OMeTAD using an easily scalable, non-thermal atmospheric pressure plasma jet (APPJ) is reported. An investigation of plasma functionalization demonstrated an enhancement in hole conductivity by over an order of magnitude from 9.4 × 10 −7 S cm −1 for the pristine film to 1.15 × 10 −5 S cm −1 for films after 5 minutes of plasma treatment. The conductivity value after plasma functionalization was comparable to that reported for 10–25% Li-TFSI-doped Spiro-OMeTAD. The increase in conductivity was correlated with a reduction in phase value observed using electrostatic force microscopy. Kelvin probe force microscopy showed an increase in work function after plasma exposure corresponding to the p-type nature of the doping. X-ray photoelectron spectroscopy revealed surface oxidation of plasma-functionalized films, as well as variation in nitrogen chemistry, with the formation of a higher binding energy quaternary nitrogen tail. Oxidation of Spiro-OMeTAD was also confirmed by the appearance of the 500 nm absorption peak using UV–vis spectroscopy. The synergistic contribution of increase in charge density in Spiro-OMeTAD due to the energetic species in the plasma jet coupled with improvement in π-π stacking of the molecules is thought to underlie the conductivity enhancement. The enhancement in positive charges can also be attributed to the formation of quinoid structures with quaternary nitrogen +N=C formed due to loss of methyl groups during plasma surface interaction. This work opens up the possibility of using an atmospheric pressure plasma jet as a simple and effective technique for doping and functionalizing Spiro-OMeTAD thin films to circumvent the detrimental issues associated with chemical dopants.

Original languageEnglish
Article number100321
Number of pages44
JournalMaterials Today Chemistry
Volume17
Early online date24 Jul 2020
DOIs
Publication statusPublished - 30 Sep 2020

Keywords

  • atmospheric pressure plasma jet
  • conductivity
  • hole transport materials
  • perovkite solar cells

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