Unidirectionally Aligned Donor-Acceptor Semiconducting Polymers in Floating Films for High-Performance Unipolar n-Channel Organic Transistors

The orientational control of semiconducting polymers (SCPs) in floating films offers several advantages over conventional solution-processing methods for device fabrication, and the unidirectional floating film transfer method (UFTM) has been applied to fabricate large-area oriented p-type SCP films. Here, UFTM can be used to prepare high-performance n-type SCP films of P(NDI2OD-T2) is reported. A strong correlation between the degree of polymer orientation and the solvent used for the preparation of P(NDI2OD-T2) floating films is observed. In particular, the size of the nanofibers aligned along the orientation direction prepared using chloroform is dramatically increased by adding a small amount of chlorobenzene. Microstructural characterization reveals that the P(NDI2OD-T2) floating films are uniaxially aligned with edge-on orientation, whereas the spin-coated films are isotropic with face-on orientation. Notably, the floating films of P(NDI2OD-T2) prepared with solvent blending have higher electron mobility with ambipolar-like device characteristics and high threshold voltage (V-TH) of approximate to 25 V. Finally, using the one-step immersion process, the introduction of an interlayer of hexa(ethylene glycol)-dithiol between the source/drain contacts and P(NDI2OD-T2) film results in a drastic improvement in device, giving unipolar n-channel transistor characteristics with a V-TH of approximate to 0 V, on/off ratio of >10(5), and mobility reliability factor of almost 100%.