What is Molecular Electronics?

Molecular electronics or "moletronics" is to use molecules as building blocks to create electronic components. These molecular electronic components include transistors, diodes, capacitors, insulators, and wires. Having control over properties on the molecular scale allows us to better understand the overall processes in an electronic device. This is turn has seen huge developments in fabrication techniques as well as improved device efficiencies.

Molecular engineering can be used to modify components of electronic devices including:

• Conductive Polymers
• Optoelectronic Materials
• Semiconducting Molecules
• Quantum Dots
• Graphene materials and Carbon Nanotubes
• Fullerenes and Non-Fullerene Acceptors
• Molecular Dyes
• Conductive Inks
• Interface Materials
• Perovskite Materials
• Self-Assembled Monolayers

Molecular Engineering in Conductive and Semiconductive Polymers

Conductive polymers are made up or repeating organic molecules called monomers. The type of bonding between monomers means the polymer can conduct electricity. Through the careful selection of the monomers and treatment of the polymer, its electronic structure can be tuned. The ability a polymer has to transport charge can be modified to meet demands of the application.

A classic example of conductive polymers for use in electronic devices are PEDOT:PSS polymers. This is a blend of conductive and non-conductive polymers, engineered on a molecular level. Different iterations have different conductivities, useful for a range of electronic applications. Molecular engineering in the development of PEDOT:PSS involves controlled polymerization, doping, and post-treatment techniques to control properties.

Molecular Engineering of Organic Molecules for Electronics

Molecular engineering changes the properties of organic molecules. Organic molecules are used widely in electronic devices for a range of applications. They usually play the role of semiconducting molecules, acceptor molecules, molecular dyes and interface layers. Here are a few examples and how molecular engineering has been used to access required properties for specific applications.

Component	Example	Molecular engineering	Properties	Function
Semiconducting Molecule	Spiro-OMeTAD	Electron Donating p-methoxy groups to increase charge (hole) mobility Spiro linkage to increase stability Lots of conjugated benzene rings	Lowered oxidation potential Improved morphological stability High glass transition temperature	Excellent hole transport material in solar cells
Acceptor Molecule	Y6	Electron-deficient benzothiadiazole core surrounded by electron-rich groups Solubilizing groups attached to core via electron-donating nitrogen atoms Two electron accepting terminals which are fluorinated	Absorption in near-infrared (NIR) region High electron mobility Low energy loss Strong aggregation of molecular backbone Favorable molecular packing	Excellent electron transport material
Molecular Dye	N3	Reduced symmetry of complex compared to [Ru(bpy)3]2+ Two electron rich isothiocyanate ligands Carboxylic acid groups for anchoring	Added bands in electronic absorption spectrum Improved light-harvesting properties HOMO orbital destabilized which reduces the band-gap of the molecule Able to self-assemble on metal oxide surfaces due to anchor groups	Superior Chromophore
Interface Material	MeO-2PACz	Rigid carbazole core with excellent hole-transporting capability Phosphonic acid anchoring group Small methoxy functional groups	Improved interface contact Tuned energy level Reduced non-radiative recombination at interface Ability to form layer on rough surface	Excellent interface material between hole transport layer and perovskite layer in PSCs

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