Solution-Processed Ambipolar Organic Thin-Film Transistors by Blending p- and n‑Type Semiconductors: Solid Solution versus Microphase Separation

Here,
we report solid solution of p- and n-type organic semiconductors as
a new type of p–n blend for solution-processed ambipolar organic
thin film transistors (OTFTs). This study compares the solid-solution
films of silylethynylated tetraazapentacene 1 (acceptor)
and silylethynylated pentacene 2 (donor) with the microphase-separated
films of 1 and 3, a heptagon-embedded analogue
of 2. It is found that the solid solutions of (1)x(2)1–x function as ambipolar semiconductors, whose hole
and electron mobilities are tunable by varying the ratio of 1 and 2 in the solid solution. The OTFTs of (1)0.5(2)0.5 exhibit relatively
balanced hole and electron mobilities comparable to the highest values
as reported for ambipolar OTFTs of stoichiometric donor–acceptor
cocrystals and microphase-separated p-n bulk heterojunctions. The
solid solution of (1)0.5(2)0.5 and the microphase-separated blend of 1:3 (0.5:0.5)
in OTFTs exhibit different responses to light in terms of absorption
and photoeffect of OTFTs because the donor and acceptor are mixed
at molecular level with π–π stacking in the solid
solution.