Energy Landscape of Vertically Anisotropic Polymer Blend Films toward Highly Efficient Polymer Light‐Emitting Diodes (PLEDs) |
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| Authors: | Muhammad Umair Hassan Yee‐Chen Liu Ali K Yetisen Haider Butt Richard Henry Friend |
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| Affiliation: | 1. Cavendish Laboratory, University of Cambridge, Cambridge, UK;2. School of Engineering, University of Birmingham, Birmingham, UK;3. Centre for Micro and Nano Devices, COMSATS Institute of Information Technology, Islamabad, Pakistan;4. School of Chemical Engineering, University of Birmingham, Edgbaston, Birmingham, UK;5. Harvard‐MIT Division of Health Sciences and Technology, Harvard University and Massachusetts Institute of Technology, Cambridge, MA, USA |
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| Abstract: | A blend of two hole‐dominant polymers is created and used as the light emissive layer in light‐emitting diodes to achieve high luminous efficiency up to 22 cd A?1. The polymer blend F81?xSYx is based on poly(9,9‐dioctylfluorene) (F8) and poly(para‐phenylene vinylene) derivative superyellow (SY). The blend system exhibits a preferential vertical concentration distribution. The resulting energy landscape modifies the overall charge transport behavior of the blend emissive layer. The large difference between the highest unoccupied molecular orbital levels of F8 (5.8 eV) and SY (5.3 eV) introduces hole traps at SY sites within the F8 polymer matrix. This slows down the hole mobility and facilitates a balance between the transport behavior of both the charge carriers. The balance due to such energy landscape facilitates efficient formation of excitons within the emission zone well away from the cathode and minimizes the surface quenching effects. By bringing the light‐emission zone in the middle of the F81?xSYx film, the bulk of the film is exploited for the light emission. Due to the charge trapping nature of SY molecules in F8 matrix and pushing the emission zone in the center, the radiative recombination rate also increases, resulting in excellent device performance. |
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| Keywords: | anisotropic films charge traps energy band diagram light‐emitting diodes polymer blends Raman spectroscopy |
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