Dresden 2017 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 22: Organic Electronics and Photovoltaics II: Doping

HL 22.9: Talk

Monday, March 20, 2017, 17:30–17:45, ZEU 260

Temperature-induced F4TCNQ desorption from p-doped P3HT films — •Hannes Hase¹, Andreas Opitz¹, Norbert Koch^1,2,3, and Ingo Salzmann¹ — ¹Humboldt-Universität zu Berlin, Supramolekulare Systeme, Germany — ²Helmholtz-Zentrum Berlin für Materialien und Energie GmbH, Bereich Solarenergieforschung, Germany — ³Jiangsu Key Laboratory for Carbon-Based Functional Materials & Devices, Institute of Functional Nano & Soft Materials (FUNSOM), Soochow University, Suzhou 215123, P.R. China

Thermal post-fabrication annealing is common practice for functional conjugated polymer (CP) films in organic photovoltaic cells, which is also applied to p-doped CPs in a number of studies. However, the typically small molecular-weight dopants, like, e.g., tetrafluoro-tetracyanoquinodimethane (F4TCNQ), can be expected to be prone to diffusion upon thermal treatment, which has been largely disregarded in pertinent literature. Here, we explore to which extent the annealing temperature impacts films of poly(3-hexylthiophene-2,5-diyl) (P3HT) doped with F4TCNQ. For temperatures beyond 60 °C, we find a reduction in conductivity with a concomitantly lowered dopant concentration, as deduced from optical and Fourier-transform infrared spectroscopy. While atomic force microscopy indicates the morphology to be essentially retained, grazing-incidence X-ray diffraction confirms the transition from a P3HT/F4TCNQ mixed crystal structure to pure P3HT and points towards F4TCNQ desorption. We conclude that, upon thermal annealing, dopant loss needs to be accounted for by adjusting the dopant concentration.