Although the performance of organic thin-film transistors (OTFTs) has increased significantly over the last decade, it still remains challenging to fabricate large area arrays of transistors with good device-to-device parameter uniformity.[1] Approaches based on the use of solution processable organic semiconductors are attractive, both in terms of throughput and the ability to pattern the semiconductor directly onto a range of substrate materials such as plastic. In terms of organic semiconductors, both soluble small molecules and polymers are viable materials classes with the former often being advantageous in terms of the higher charge carrier mobilities that can be obtained in OTFTs. Despite this significant advantage however, the processing of highly crystalline small molecules into uniform thin films over large area substrates is often much more challenging than polymers, especially with respect to device to device parameter spread. This can be related to the intrinsic anisotropy of transport in polycrystalline small molecule based films, in addition to pronounced grain boundary effects.[2] An attractive approach to these processing challenges is to combine the high mobility properties of small molecules with the advantageous processability of polymers and fabricate blend based OTFTs.[3] It has recently been shown that simple physical blending of a small molecule and a polymer matrix material affords control of the rate and degree of crystallization of the small molecule component during film formation. This has been successfully demonstrated with blends of several p-type organics, such as 6, 13-bis (triisopropylsilylethynyl) pentacene (TIPS-pentacene)[4] and 2, 8-difluoro-5, 11-bis (triethylsilylethynyl) anthradithiophene (diF-TESADT),[5] in combination with different types of binder polymers. OTFTs fabricated from such semiconducting blends have shown hole mobilities over 5 cm 2 V− 1 s− 1 with excellent device reproducibility.[5, 6]

Despite the great potential of the small molecule-polymer blend approach, the methodology has yet to be applied to electron transporting (n-type) organic semiconducting systems. The demonstration of such materials and devices are a key element for the development of next generation large-scale integrated circuits based on complementary logic. Unfortunately, progress in the area of n-type organics has generally lagged the development of p-types, and there are far fewer examples of solution processable, high mobility n-type polymers and small molecules.[7] Of particular importance is the development of air stable materials ie compounds that are not susceptible to atmospheric oxidants such as oxygen and water. Several studies have suggested lowest unoccupied molecular orbital (LUMO) levels below− 4 eV are necessary for air stable electron transport,[8] and the development of materials combining high mobility, good stability and solution processability has proved a particular challenge. A promising class of materials that could potentially address the issues of deep LUMO level (ie, ambient stability) and high electron mobility (high performance), are small molecule compounds based on diketopyrrolopyrrole (DPP) as the core building block.[9] The fused ring of DPP is known to have a strong tendency to stack in the solid state, possibly driven by very strong electrostatic and hydrogen bonding interactions. This rather unique property has recently been exploited for the demonstration of a number of high performing p-type as well as ambipolar DPP containing polymers.[10] On the contrary, small molecules based on simple DPP derivatives have so far been either p-type,[11] or displayed very low electron mobilities.[12 …