Heterojunctions between zinc oxide nanostructures and organic semiconductor

Sammanfattning: Lighting is a big business, lighting consumes considerable amount of the electricity. These facts motivate for the search of new illumination technologies that are efficient. Semiconductor light emitting diodes (LEDs) have huge potential to replace the traditional primary incandescent lighting sources. They are two basic types of semiconductor LEDs being explored: inorganic and organic semiconductor light emitting diodes. While electroluminescence from p-n junctions was discovered more than a century ago, it is only from the 1960s that their development has accelerated as indicated by an exponential increase of their efficiency and light output, with a doubling occurring about every 36 months, in a similar way to Moore's law in electronics. These advances are generally attributed to the parallel development of semiconductor technologies, optics and material science. Organic light emitting diodes (OLEDs) have rapidly matured during the last 30 years driven by the possibility to create large area light-emitting diodes and displays. Another driving force to specifically use semiconducting polymers is the possibility to build the OLED on conventional flexible substrates via low-cost manufacturing techniques such as printing techniques, which open the way for large area productions.This thesis deals with the demonstration and investigation of heterojunction LEDs based on p-organic semiconductor and n-ZnO nanostructures. The ZnOorganic heterojunctions are fabricated using low cost and simple solution process without the need for sophisticated vacuum equipments. Both ZnO-nanostructures and the organic materials were grown on variety of substrates (i.e. silicon, glass and plastic substrates) using low temperature methods. The growth mechanism of the ZnO nanostructures has been systematically investigated with major focus in ZnO nanorods/nanowires. Different organic semiconductor materials and device configurations are explored starting with single polymer emissive layer ending up with separate emissive and blocking layers, or even blends. Interestingly, the photoluminescence and electroluminescence spectra of the hybrid LEDs provided a broad emission band covering entirely the visible spectrum [?400-?800nm]. The hybrid light emitting diode has a white emission attributed to ZnO intrinsic defects and impurities in combination with the electroluminescence from the conjugated polymers. The ZnO nanostructures in contact with a high workfunction electrode constitute an air stable electron injecting contact for the organic semiconductor. Hence, we have shown that a white light emission can be achieved in a ZnO-organic hybrid light emitting diode using cheap and low temperature growth techniques for both organic and inorganic materials.