Work function tuning of electrode materials with small molecule surface modifiers
Kim, Hye Kyung
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Energy level alignment at metal/organic interfaces plays a critical role in charge transport across the interfaces within organic and optoelectronic devices. To control the barriers to injection/collection, dipolar surface modifiers can be introduced at the interface to tune the work- function of the electrode material. This results in a shift of the frontier molecular orbitals of the organic semiconductor upon contact with the modified-electrode. An appropriate shift in one direction facilitates electron transport and the opposite direction hole transport. In this work, new small molecule surface modifiers were synthesized and deposited on electrode materials, namely indium tin oxide (ITO) and gold to reduce their work-functions to be potential candidates for low work-function electron selective electrodes. Amines – N-oxide and N-heterocyclic carbenes, in addition to chalcogens – phosphine sulfide phosphines and N-heterocyclic thiones and selones were investigated for their work-function reducing capabilities and surface coverage. All the materials successfully reduced the work-function of the modified electrodes, with the magnitude of the shift dependent, to a degree, on the thickness of the deposited film.