Engineered solid-state aggregates in brickwork stacks of n-type organic semiconductors: a way to achieve high electron mobility.

Efficient, economically viable n-type organic semiconductor materials suitable for solution-processed OFET devices with high electron mobility and ambient stability are scarce. Merging these attributes into a single molecule remains a significant challenge and a careful molecular design is needed. To address this, synthetic viability (achievable in fewer than three steps) and using cost-effective starting materials are crucial. Our research presents a strategy that meets these criteria using naphthalene diimide (NDI) core structures. The approach involves a simple synthesis process with a cost of $ 5-10 per gram for the final products. This paper highlights our success in scaling up the production using affordable known reagents, creating ambient condition solution-processed OFET devices with impressive electron mobility, on-off current ratio (1 cm2 V-1 s-1 and I on/I off ∼ 109) and good ambient stability (more than 100 h). We conducted a comprehensive study on EHNDIBr2, a material that demonstrates superior performance due to its unique supramolecular arrangement in its brickwork stack. This was compared with two similar structures to validate our findings. The superior performance of EHNDIBr2 is attributed to the effective interlocking of charge-hopping units within the NDI core in its brickwork stack. Our findings include detailed electronic, spectroscopic, and microscopic analyses of these layers.

Ambient stable solution-processed organic field effect transistors from electron deficient planar aromatics: effect of end-groups on ambient stability.

Ambient stable solution processed n-channel organic field effect transistors (OFETs) are essential for next-generation low-cost organic electronic devices. Several molecular features, such as suitable orbital energy levels, easy synthetic steps, etc., must be considered while designing efficient active layer materials. Here, we report a case of improved ambient stability of solution-processed n-type OFETs upon suitable end-groups substitution of the active layer materials. A pair of core-substituted napthalenediimide (NDIFCN2 and EHNDICN2) derivatives with alkyl and perfluorinated end groups are considered. The transistor devices made out of these two derivatives exhibited largely different ambient stability behavior. The superior device stability (more than 25 days under ambient conditions) of one of the derivatives (NDIFCN2) was ascribed to the presence of fluorinated end groups that function as hydrophobic guard units inhibiting moisture infiltration into the active layer, thereby achieving ambient stability under humid conditions (>65% relative atmospheric humidity). Molecular level optical and electrochemical properties, thermal stability, and the solution-processed (spin coat and drop cast active layers) device characteristics are described in detail. Our findings highlight the requirement of hydrophobic end groups or sidechains for ambient stability of active layer materials, along with deep LUMO levels for ambient stability.