Exciton dynamics and charge transport in organic heterostructure

Author(s)

Gustavo Targino Valente

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Instituto de Física de São Carlos (IFSC/BT)
• Defense date: 2017-12-07

Examining board members

Francisco Eduardo Gontijo Guimarães; Luiz Alberto Cury; Roberto Mendonça Faria; Yara Galvão Gobato; Lucas Fugikawa Santos

• Advisor: Francisco Eduardo Gontijo Guimarães

Abstract

In this study the exciton migration, energy transfer and charge transport in ultrathin organic heterostructure formed by semiconductor polymer and chlorophyll molecules were investigated. The energetic tuning between these materials promotes organic heterostructures with energetic modulation capable of trapping excitons and charges showing an application potential in Organic Light Emitting Diodes (OLEDS). Amorphous polyfluorenes (PFO) and chlorophyll a (chla) were prepared using self-assembly combined with spin-coating methods and characterized by confocal laser scanning microscopy and spectroscopic techniques. Photophysical processes were investigated using confocal and life-time microscopy and the results interpreted from the model of Förster energy combined with the Miller-Abrahams rate as well as the exciton diffusion equation. These results provided a relationship between the exciton migration in the PFO film and the non-radiative energy transfer from polymer to chla molecules. An efficient transfer of energy equal to 94% was observed. Method of the Monte Carlo simulation were implemented to investigate the charge transport in this disordered organic system. Using this method, the charge dynamics with and no potential well layer was studied. Electrical properties obtained, such as electric mobility and diffusion coefficient, are in agreement with literature. It was estimated a charge fill rate in the potential well equal to 1010 holes/s for 1 MV/cm and this parameter increases with the electric field. This approach has been shown to be an interesting alternative for the experimental design of OLEDs composed by organic heterostructure. (AU)

• FAPESP's process: 13/27047-7 - Optoelectronic properties of organic light-emitting diode containing quantum wells and barriers of biomolecules
• Grantee: Gustavo Targino Valente
• Support Opportunities: Scholarships in Brazil - Doctorate