Universal ohmic electron and hole contacts for organic light-emitting diodes and electronics (Conference Presentation)

Abstract

An ohmic electrical contact is one that allows the largest possible current density limited by space-charge effects to be injected into the adjoining semiconductor. This is key to maximizing device efficiency and reliability, and thus fundamental to all semiconductor devices. A long-standing challenge for organic (and other solution-based) electronics is the lack of a general solution-based compatible strategy to fabricate ohmic contacts at will. To overcome these challenges, we have recently developed self-compensated heavily-doped polymers with ultrahigh and ultralow workfunctions, and polyelectrolyte interlayers for 2D interface doping. Unprecedented p- and n-doped conductive polymer films over an ultrawide work function range of 3.0 eV to 5.8 eV have been obtained, enabling solution-processed ohmic contacts for light-emitting diodes, solar cells, photodiodes and transistors. Self-aligned doped contacts have also become possible. We anticipate that these strategies will enable ohmic contacts to also be made to other advanced semiconductors, including quantum dots, nanotubes and 2D materials, and open up new and technologically interesting device architectures for various photonic and non-photonic applications. Using these materials, we have developed new understanding of the physics of work function and ohmic contacts relating to doped organic semiconductors. The localization of charge carriers in organic semiconductors, different from conventional band semiconductors, leads to important differences in the essential physics.