Hot injection synthesis of CuInS2 nanocrystals using metal xanthates and their application in hybrid solar cells

Verena Perner,Birgit Kunert,Karin Wewerka,Thomas Rath,Peter Zach,Ilse Letofsky-Papst,Franz Pirolt,Gregor Trimmel,Mathias Hobisch,Otto Glatter

doi:10.1039/c8nj04823a

Abstract

Copper indium sulfide nanocrystals with sizes of 3–4 nm were synthesized from metal xanthates in a hot injection reaction. After ligand exchange, their performance as acceptors in polymer/nanocrystal hybrid solar cells was evaluated.

Highlights

Compared to Cd- or Pb-containing sulfide or selenide nanocrystals, the application of CuInS2 nanocrystals in bulk heterojunction hybrid solar cells is less researched and the performance of CuInS2 nanocrystal based bulk heterojunction solar cells remained much lower
Whereas the formation to the metal sulfide proceeds via the thermally activated Chugaev reaction, the reaction pathway might change in the presence of alkyl amines as we have recently shown for a room temperature synthesis of CuInS2 nanocrystals using oleylamine.[42]
When only oleylamine was used as capping ligand, despite the good results we obtained in a room temperature synthesis,[42] extremely small nanocrystals were synthesized, which could not be precipitated and separated from the reaction solution

Summary

Introduction

Compared to Cd- or Pb-containing sulfide or selenide nanocrystals, the application of CuInS2 nanocrystals in bulk heterojunction hybrid solar cells is less researched and the performance of CuInS2 nanocrystal based bulk heterojunction solar cells remained much lower. In most cases molecules such as oleylamine,[34] oleic acid, octadecene, trioctylphosphine or dodecanethiol are used as ligands and copper and indium salts (e.g. halides, acetates, acetylacetonates) in combination with a sulfur source (e.g. elemental sulfur, thiourea, dodecanethiol) as precursors.[1] single source precursors[37,38] and precursors which contain the metal and sulfur source in one compound (e.g. dithiocarbamates)[39] are already investigated In this regard, metal xanthates have been proven to be very suitable.[40,41,42,43,44,45] Examples for a hot injection synthesis of CuInS2 nanoparticles comprise the syntheses from the corresponding copper and indium ethyl xanthates using glycol[38] or trioctylamine as solvent and oleylamine/trioctylphosphine as ligands.[39] Alternatively, nanocrystals have been isolated via the decomposition of copper and indium xanthates in a mixture of o-dichlorobenzene as solvent and oleylamine/ trioctylphosphine[40] or poly(3-hexylthiophene) (P3HT) as polymeric ligand.[41] a series of xanthates with different alkyl side chains was investigated for the synthesis of CuInS2 nanocrystals with hexagonal and cubic phase by Al-Shakban et al.[37] Whereas the formation to the metal sulfide proceeds via the thermally activated Chugaev reaction, the reaction pathway might change in the presence of alkyl amines as we have recently shown for a room temperature synthesis of CuInS2 nanocrystals using oleylamine.[42]. We evaluate the performance of the ligand-exchanged nanocrystals in polymer/nanocrystal bulk heterojunction solar cells

Sample and solar cell preparation

Characterisation techniques

Results and discussion

Conclusions