Ultrafast Transport of Triplet Excitons in the Polymeric Semiconductor
Gangadhar Banappanavar a, Sumukh Vaidya a, Urvashi Bothra b, Lohitha Hegde c, Kamendra Sharma c, Richard Friend d, Dinesh Kabra a
a Department of Physics, Indian Institute of Technology, Bombay, Powai, Mumbai, Maharashtra, India
b IITB-Monash Research Academy, IIT, 319 IITB-Monash Research Academy, IIT, Powai, Mumbai, Maharashtra, India
c Department of Chemistry, Indian Institute of Technology, Bombay, Powai, Mumbai, India
d Optoelectronics Group, Cavendish Laboratory, , Cambridge (UK), JJ Thomson Avenue, Cambridge, United Kingdom
Proceedings of SUNRISE September Symposium 2021 ‘Powering Green Recovery’ (SUNRISEIII)
Online, Spain, 2021 September 20th - 22nd
Organizers: Hari Upadhyaya, Adrian Walters, James Durrant, Sara Walters and Georgia Bevan
Poster, Gangadhar Banappanavar, 016
Publication date: 14th September 2021
ePoster: 

Due to their potential for high-efficiency optoelectronic devices, the behavior of organic semiconductors has garnered increasing interest in recent years. Understanding the transport of excitons by diffusion of singlets and triplets is essential for developing efficient optoelectronic devices. Measuring the characteristically non-emissive triplets, however, continues to challenge the field. In this work, we have developed a unique method to trace the position of the triplet exciton in the emissive layer of organic light emitting diode (OLEDs) by analyzing angle-resolved delayed electroluminescence emission patterns as a function of time. This study could provide exciton transport kinetics in the transverse direction from the substrate plane. Furthermore, direct visualization of the delayed photoluminescence imaging technique could provide lateral transport kinetics of triplet excitons. We have studied the effect of polymer chain packing on triplet diffusion in the polyfluorene based polymeric system, which is known to give efficient OLED efficiency for display devices. Further, this polyfluorene system exhibits an efficient triplet-triplet fusion process, which provides singlet excitons as delayed fluorescence and becomes a tool to study triplet exciton kinetics. Results suggest that, in the thicker polymeric semiconductor films, diffusivity approaches close to ultrahigh 10-3 cm2s-1, which is similar to the values that are reported for acene-based molecular crystalline thin films. Our results also provide important insight into efficient electroluminescence in unusually thick (1.2 mm) polyfluorene-based emissive layers of OLEDs.

We thank Cambridge Display Technology (CDT) Ltd. for supplying the F8BT. We also acknowledge the support of the NCPRE in allowing the use of the device fabrication facility. G.B. acknowledges funding support of DST for the research fellowship. R.H.F. and D.K. acknowledge the funding support from the RCUK- funded SUNRISE project. We also would like to acknowledge Christopher R. McNeil for the discussion on SAXS data.

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