Interfaces in Organic and Hybrid Optoelectronics
The function and performance of organic and hybrid optoelectronic devices is tightly related to their nanostructure and the electronic structure of the surfaces and hetero-interfaces of the device components. Surface and interface sensitive techniques such as X-ray and ultra-violet photoemission spectroscopies (XPS and UPS, respectively) are unique tools to probe the composition and density of filled states in the material, crucial for the understanding of charge separation, transport and extraction in energy materials.
Many organic/organic and organic/TiO2 interfaces have been extensively investigated, and efficient optoelectronic devices – such as polymer:fullerene and Grätzel solar cells – have been successfully demonstrated. In our academic research, we focus on the study of the vast array of interfaces that are far less investigated. Through our work, we have demonstrated that once the interfacial structure is resolved and the physico-chemical processes are well understood, it is possible to tame even disordered interfaces to be utilized in a broad range of optoelectronic applications.
Organic light-emitting diodes (OLEDs)
The efficiency of OLEDs is largely determined by the charge injecting properties of the organic/inorganic interfaces between the active layer and the electrodes. While hole-injection has been intensively investigated and optimised by various research groups, few reports exist studying and optimising the electron-injection into the device. Our research in the field of OLEDs is focused on the unraveling the role of interfacial interactions and through that control and modification of the electron-injecting electrode. We use organic and inorganic modifiers, such as self-assembled monolayers, to enhance the electron injection properties of the cathode. A similar approach can be used to modify a single contact in a light-emitting field effect transistor (LEFET), which can dramatically increase the electron injection and as a result the efficiency of such a device.
Organic and hybrid photovoltaic devices (PVs)
It has been demonstrated that in order to achieve high efficiencies in polymer PVs, the active layer should consist of two materials intermixed in a single layer, called a bulk heterojunction. In hybrid PVs, a nanostructured oxide layer replaces the acceptor component in the active layer blend and acts as a template in which the polymer is infiltrated. We investigate this alternative approach and focus on the study of the polymer/oxide interface.