Abstract
Contact potential difference (CPD) measurements of the relative work functions of a range of organic semiconductor thin films show that oxygen causes effective p-type doping (with work functions increasing 0.1-0.3 eV). This doping effect is found to be reversible by exposure to high vacuum or heating in inert atmosphere. The mechanism of doping is explained by a model, based on a reversible formation of an O-substrate charge transfer state. Conductivity measurements of p-phthalocyanine films at variable temperatures support this doping model. The oxygen doping effect is consistent with filling of tail states in the gap, as shown by the increase of activation energy of hole transport with decreased O-doping, and by the good fit between experimental data and simulations of the in-gap density of states. A model hybrid solar cell configuration also shows the effect of doping by O2 and corroborates the fact that O-doping fills the tail states in the system.
Original language | English |
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Pages (from-to) | 966-972 |
Number of pages | 7 |
Journal | Organic Electronics |
Volume | 14 |
Issue number | 3 |
DOIs | |
State | Published - Mar 2013 |
Externally published | Yes |
Funding
We thank Achim Schöll (Univ. Würzburg, Germany) for providing us PTCDA and PTCDI. We also thank Antoine Kahn (Princeton University, USA) and K.L. Narasimhan (IIT Bombay, India) for invaluable suggestions. We thank Robert Lovrincic (WIS) for his help in transport measurements and Sivan Kober (WIS) for providing glass substrates with Inter-digitated gold fingers. RR was financially supported by the MIT International Science and Technology Initiatives (MISTI) during his stay at WIS. We are grateful to the Israel Ministry of Science and Technology, the Wolfson family trust, the Helmsley trust and the Nancy and Stephen Grand Center for Sensors and Security for partial support. DC holds the Sylvia and Rowland Schaefer Chair in Energy research.
Funders | Funder number |
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MIT International Science and Technology Initiatives |
Keywords
- Charge transfer complex
- Doping
- Gap states
- Tail states