Organic semiconductors exhibit many attractive traits, such as their low-cost, solution processability, transparency and mechanical flexibility. They could fulfil various electronic functionalities on almost any substrate rather than being limited to the rigid Si-wafers used in traditional integrated circuits. For example, commercial organic light-emitting diodes1 (OLEDs) that have recently emerged as a strong flat-panel display technology are fabricated on transparent glass substrates, whereas organic thin-film transistors (OTFTs) can be realized on traditional Si/SiO2 and plastic substrates alike.

Low field-effect mobility of organic semiconductors has inhibited the commercial debut of OTFTs. Following the progress made towards synthesizing high-mobility organic polymers and small molecules, several materials with mobility superior to amorphous silicon2,3 have been successfully demonstrated. However, until now the best performing OTFTs have been almost exclusively fabricated on Si, which, unlike plastic substrates, ensures a higher quality of the semiconductor–dielectric interface. In a transistor fabricated on doped silicon wafers, charge trapping at the semiconductor–SiO2 interface is known to cause performance deterioration, but this issue can be readily circumvented by surface functionalization with self-assembled monolayers (SAMs). Surface passivation with SAMs effectively lowers the dielectric surface energy and reduces the interface trapping density, resulting in OTFTs with improved characteristics, but it is not applicable for plastic substrates and, therefore, for flexible electronic devices.

On page 139, Yokota et al. present an alternative passivation method that works on arbitrary surfaces including polymers and has been demonstrated to improve the performance of flexible OTFTs in a way similar to high-quality aliphatic SAMs on inorganic oxides. The approach is based on recently developed two-dimensional triptycene films4 that serve as part of a dielectric layer but unlike other SAMs do not require specific covalent bonding sites. That is to say, the fabrication of high-quality OTFTs with reproducible characteristics is no longer limited to rigid silicon but can be obtained on any flexible substrate, providing the benefit of the significantly extended functionality of organic electronic devices and circuits. Thus, it is now possible to fabricate both p- and n-type OTFTs as well as complementary inverters and ring oscillators with excellent static and dynamic performance on arbitrary substrates.