Charge Transfer Absorption and Emission at ZnO/Organic Interfaces
Fortunato Piersimoni1, Raphael Schlesinger, Johannes Benduhn2
1†Institute of Physics and Astronomy, University of Potsdam, Karl-Liebknecht-Straße 24-25, 14476 Potsdam, Germany.
The Journal of Physical Chemistry Letters
|August 12, 2015
Summary
Hybrid charge transfer states (HCTS) between α-NPD and ZnO emit near-infrared light. Their energy is tunable by modifying the ZnO interface, confirming radiative recombination.
Area of Science:
- Organic electronics
- Materials science
- Photophysics
Background:
- Investigating charge transfer dynamics at organic-inorganic interfaces is crucial for advancing optoelectronic devices.
- Hybrid charge transfer states (HCTSs) are key to understanding energy transfer and recombination processes.
- The interface between organic semiconductors like α-NPD and metal oxides such as ZnO presents unique electronic properties.
Purpose of the Study:
- To investigate the formation and radiative decay of hybrid charge transfer states (HCTSs) at the α-NPD/ZnO interface.
- To elucidate the origin of near-infrared (NIR) emission observed in these bilayer devices.
- To explore the influence of interface energy level alignment on HCTS properties and device performance.
Main Methods:
- Fabrication of bilayer devices comprising α-NPD and ZnO.
- Spectrally resolved electroluminescence (EL) measurements to detect emission.
- External quantum efficiency (EQE) measurements to probe charge carrier dynamics.
- Surface modification of ZnO using self-assembled monolayers (SAMs) of phosphonic acids to tune interface energetics.
Main Results:
- Distinct NIR emission peaks were observed in EL spectra, confirming radiative decay of HCTSs below bulk material emission energies.
- EQE spectra showed red-shifted contributions, correlating with NIR EL emission.
- A linear dependence of NIR EL peak position on the interface energy gap (Eint) was established after ZnO surface modification.
- A linear relationship was found between open-circuit voltage and the charge state energy.
Conclusions:
- The observed NIR emission is unambiguously attributed to radiative recombination of electrons in ZnO and holes in α-NPD, originating from HCTSs.
- Tuning the interface energy level alignment via SAMs provides a method to control HCTS emission energy.
- These findings offer insights into managing charge transfer and recombination at organic-inorganic interfaces for device applications.
Keywords:
electroluminescencemetal oxideopen-circuit voltageorganic semiconductorself-assembled monolayerMore Related Videos
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