Investigation of interfaces in polymeric light-emitting diodes (PLEDs) by SFG spectroscopy

• Grant number: 13/07328-1
• Support Opportunities: Scholarships in Brazil - Doctorate
• Start date: July 01, 2013
• End date: December 21, 2017
• Field of knowledge: Physical Sciences and Mathematics - Physics - Condensed Matter Physics
• Principal Investigator: Paulo Barbeitas Miranda
• Grantee: Douglas José Correia Gomes
• Host Institution: Instituto de Física de São Carlos (IFSC). Universidade de São Paulo (USP). São Carlos , SP, Brazil
• Associated research grant: 07/08688-0 - Electronic and optoelectronic polymer devices, AP.TEM
• Associated scholarship(s): 15/21872-1 - Studying organic transistors by charge modulation spectroscopy (CMS), BE.EP.DR

Abstract

This proposal addresses the study of interfaces in optoelectronic devices based on conjugated polymers (CP), more specifically in polymeric light-emitting diodes (PLEDs). We will investigate both CP-metal and CP-conducting oxide interfaces by Sum-Frequency Generation (SFG) vibrational spectroscopy. This problem is quite important since fundamental phenomena that are essential to the performance of organic devices take place at this interface, such as charge injection and collection. Several studies in the literature focus on the CP-metal interface. Some are theoretical studies requiring experimental verification, and several others probe interfaces which are prepared in a quite different way from those present in real devices (such as ultrathin metallic layers), or use analytical tools without specificity to interfaces. In this regard, the advantage of our proposal over previous studies is on the use of SFG spectroscopy to probe interfaces found in functional PLEDs prepared in the usual way. SFG spectroscopy allows one to obtain the vibrational spectrum of molecules at an interface without bulk contribution, from which is possible to determine the molecular arrangement at the interfaces by a quantitative analysis of the CP's C-C vibrations, which are the molecular regions directly involved in the operation of optoelectronic devices. Furthermore, a simple and qualitative analysis of the SFG spectra leads to the recognition of doping (formation of space charge) at electrode interfaces. We also plan to compare the SFG spectra of the interfaces in our devices obtained immediately after preparation, and after different degradation protocols (by electric current and/or exposure to ambient conditions). The goal is to look for any correlation between device performance degradation and changes in molecular structure at the interfaces, potentially even finding the molecular origin for such performance degradation. With this we hope to understand the role played by interfaces on the device degradation, and perhaps even suggesting ways to prevent it, for example, by device architecture and/or molecular engineering of the active layer. This study could have important implications to the improvement of performance and durability of organic optoelectronic devices. (AU)

Scientific publications

(References retrieved automatically from Web of Science and SciELO through information on FAPESP grants and their corresponding numbers as mentioned in the publications by the authors)

MOTTI, SILVIA G.; CARDOSO, LILIAN S.; GOMES, DOUGLAS J. C.; FARIA, ROBERTO M.; MIRANDA, PAULO B.. Probing Device Degradation and Electric Fields in Polymeric Field-Effect Transistors by SFG Vibrational Spectroscopy. Journal of Physical Chemistry C, v. 122, n. 19, p. 10450-10458, MAY 17 2018. (14/50869-6, 13/07328-1, 15/24908-7, 14/01595-0)

Academic Publications

(References retrieved automatically from State of São Paulo Research Institutions)

GOMES, Douglas José Correia. Study of organic transistors by nonlinear vibrational spectroscopy and charge modulation microscopy. 2018. Doctoral Thesis - Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD) São Carlos.