Electron–Hole Recombination in Uniaxially Aligned Semiconducting Polymers

Authors


  • We gratefully acknowledge funding from the Engineering and Physical Sciences Research Council (EPSRC), the Gates Cambridge Trust (J. Z.), the EU Integrated Project NAIMO (No NMP4-CT-2004-500355) (C. G.), and helpful discussions with Dr. Martijn Kemerink. We thank Dr. Ahmed Nejim from Silvaco for adapting the ATLAS code for the device simulations. Supporting Information is available online from Wiley InterScience or from the authors.

Abstract

A promising, general strategy for improving performance of optoelectronic devices based on conjugated polymer semiconductors is to make better use of the fast intrachain transport along the covalently bonded polymer backbone. Little is known, however, about how the recombination rate between electrons and holes would be affected in device structures in which current flow is primarily along the polymer chain. Here a light-emitting field effect transistor (LFET) structure with a uniaxially aligned semiconducting polymer is used to show that the width and shape of the recombination zone depend strongly on polymer alignment. For alignment of the polymer parallel to the current the emission zone is 5–10 times wider than for perpendicular alignment. 2D drift-diffusion modeling is used to show that such significant widening of the recombination zone in the case of parallel alignment implies that the recombination rate constant is more than 100 times lower than expected for standard Langevin recombination. On the basis of Monte Carlo modeling it is proposed that such unexpected weak recombination is a result of the significant mobility anisotropy of the aligned polymer. These results provide new fundamental insight into the recombination physics of polymer semiconductors.

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