Gate Voltage Dependent Resistance across Interspherulite Boundaries in Solution-Processed Organic Semiconductor Thin Films

Grain boundaries formed by impinging spherulites in solution-processed organic semiconductor thin films limit charge transport in organic field-effect transistors that comprise these polycrystalline active layers. Thin films of triethylsilylethynyl anthradithiophene (TES ADT) exhibit limited order upon spin-coating; subsequent exposure to 1,2-dichloroethane vapor induces growth of TES ADT spherulites, with a mixture of low-angle (LA) and high-angle (HA) interspherulite boundaries (ISBs) defining neighboring spherulites. Our ability to control the directionality of TES ADT growth allows us to prescribe the formation of ISBs, forming exclusively LA [0$\pm$20$^{\circ}$] and HA ISBs [90$\pm$20$^{\circ}$] over macroscopic distances. Gated four-point probe transistor measurements allow us to quantify differences in resistance within spherulites and across these LA and HA ISBs as the devices are switched from ``off'' to ``on'' states. Surprisingly, for devices in the ``on'' state, the gate-independent resistances across LA [6$\pm$3M$\Omega$] and HA ISBs [16$\pm$6M$\Omega$] remain quantitatively different from that within an individual spherulite [1.9$\pm$0.7M$\Omega$], suggesting that the angle of mismatch of the ISB continues to affect charge transport, even after all traps are filled.