A method for identifying the cause of inefficient salt-doping in organic semiconductors. Issue 36 (24th August 2022)

• Record Type: Journal Article
• Authors: Rahimichatri, A.; Liu, J.; Jahani, F.; Qiu, L.; Chiechi, R. C.; Hummelen, J. C.; Koster, L. J. A.
• Is Part Of: Journal of materials chemistry. Volume 10:Issue 36(2022)
• Page Start: 13093
• Page End: 13098
• Publication Date: 2022-08-24
• Subjects: Materials -- Periodicals; Chemistry, Analytic -- Periodicals; Optical materials -- Research -- Periodicals; Electronics -- Materials -- Research -- Periodicals; 543.0284
• DOI: 10.1039/d1tc06062g
• Languages: English
• ISSNs: 2050-7526

Abstract

Abstract : To assess if salt-doping leaves anions and cations in the film, limiting the conductivity, one can apply a bias voltage and monitor the conductivity over time. If the doping is limited by unwanted ions, then the conductivity will increase with time. Abstract : Doping to enhance the electrical conductivity of organic semiconductors is not without its challenges: The efficacy of this process depends on many factors and it is not always clear how to remedy poor doping. In the case of doping with salts, one of the possible causes of poor doping is a limited yield of integer charge transfer resulting in the presence of both cations and anions in the film. The charge of such ions can severely limit the electrical conductivity, but their presence is not easily determined. Here we introduce a set of simple conductivity measurements to determine whether poor doping in the case where the dopant is a salt is due to limited integer charge transfer. By tracking how the conductivity changes over time when applying a bias voltage for an extended amount of time we can pinpoint whether unwanted ions are present in the film. Firstly, we introduce the principle of this approach by performing numerical simulations that include the movement of ions. We show that the conductivity can increase or decrease depending on the type of ions present in the film. Next, we show that the movement of these dopant ions causes a build-up of space-charge, which makes the current–voltage characteristic non-linear. Next, we illustrate how this approach may be used in practice by doping a fullerene derivative with a series of organic salts. We thus provide a tool to make the optimization of doping more rational.