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D7.1.1

CdSe Nanoparticle/Metal-Organic Inks For Printable Electronics Douglas L. Schulz CeraMem Corporation, Waltham, MA 02453, U.S.A. ABSTRACT The research objective of this project was the spray deposition of CdSe films using a nanoparticle CdSe suspension as the precursor ink. This ink consisted of CdSe nanoparticles (nano-CdSe) mixed with a “reactive dispersant” in a non-aqueous solvent. The reactive dispersant, a metal-organic molecule, served two purposes; (1) to form a dispersed CdSe suspension at room temperature, and (2) to thermally “unzip” giving CdSe and a byproduct. The CdSe thereby formed could be deposited at the grain boundaries and serve to physically and electrically connect the CdSe nanoparticles at moderate, plastic-compatible temperatures. If electronics-grade CdSe layers could be produced at low deposition temperatures, this approach may be applicable to printed CdSe-based thin film field-effect transistors (TFTs) on flexible substrates. INTRODUCTION The TFT is the active element of an active-matrix liquid crystal display, functioning as a switch to turn a pixel on or off. CdSe was the semiconductor used in the pioneering active matrix work of the 1970’s.1,2 CdSe TFTs possess high mobility (µ = 100-400 cm2/V•s) and thus have the potential to operate at high frequencies with large current densities. CdSe TFTs, however, never became fully integrated into active-matrix LCD products. This may be a consequence of the hesitancy of display design engineers to move away from silicon-based processing – the electronics industry’s standard – given the complexities associated with photolithographic processes for CdSe. Printing offers a non-lithographic based deposition approach that could overcome existing hurdles towards a manufacturing process for CdSe TFTs. One of the main challenges associated with the development of printed metal chalcogenide electronic materials is the growth of pure and appropriately doped materials. For spray deposition of particle-in-liquid suspensions, the molecules used to stabilize the precursor ink often result in contamination (e.g., C) at the grain boundaries. Unfortunately, a 600 °C anneal in air to burn out the C (as is used for oxide-based materials) is not practical for most metal chalcogenide systems as such treatment leads to formation of deleterious phases with substandard electrical performance. There is a need for a dispersant that leaves the growth surface cleanly and does not result in grain boundary contamination. Spray deposition of hybrid nanoparticle/metal-organic inks offers a unique solution to the problem. These hybrid systems include nanoparticles and metal-organics where the metalorganic species thermally transform at moderate temperature. The nonvolatile decomposition products of this reaction serve to bond nanoparticles to other nanoparticles and to the substrate. A hybrid system must invoke suspension stability prior to deposition and evolve an appropriately pure product after deposition.

D7.1.2

EXPERIMENTAL DETAILS While the nature of the cadmium