Chemical Annealing of Zinc Tetraphenylporphyrin Films: Effects on Film Morphology and Organic Photovoltaic Performance

Cong Trinh, Matthew T. Whited, Andrew Steiner, Christopher J. Tassone, Michael F. Toney, Mark E. Thompson

Research output: Contribution to journalArticlepeer-review

21 Scopus citations

Abstract

We present a chemical annealing process for organic thin films. In this process, a thin film of a molecular material, such as zinc tetraphenylporphyrin (ZnTPP), is exposed to a vapor of nitrogen-based ligand (e.g., pyrazine, pz, and triazine, tz), forming a film composed of the metal-ligand complex. Fast and quantitative formation of the complex leads to marked changes in the morphology and optical properties of the film. X-ray diffraction studies show that the chemical annealing process converts amorphous ZnTPP films to crystalline ZnTPP•ligand films, whose porphryin planes lie nearly parallel to the substrate (average deviation is 8° for the ZnTPP•pz film). Organic solar cells were prepared with ZnTPP donor and C 60 acceptor layers. Devices were prepared with and without chemical annealing of the ZnTPP layer with a pyrazine ligand. The devices with chemically annealed ZnTPP donor layer show an increase in short-circuit current (J SC) and fill factor (FF) relative to analogous unannealed devices, presumably because of enhanced exciton diffusion length and improved charge conductivity. The open circuit voltages (V OC) of the chemically annealed devices are lower than their unannealed counterpart because of enhanced polaron pair recombination at the donor/acceptor heterojunction. A net improvement of 5-20% in efficiency has been achieved, after chemical annealing of ZnTPP films with pyrazine. © 2012 American Chemical Society.
Original languageEnglish (US)
Pages (from-to)2583-2591
Number of pages9
JournalChemistry of Materials
Volume24
Issue number13
DOIs
StatePublished - Jun 26 2012
Externally publishedYes

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