Operational and Environmental Stability Assessment of Silicon and Copper Phthalocyanine-Based OTFTs

When developing new materials for organic electronics, understanding how they will perform and change over time is critical. Typical bias stress exposure experiments provide limited information on the materials' performance in applications which involve multiple charging and discharging steps. Here, organic thin film transistors (OTFTs) are characterized for 48-72 h straight in air and in N₂ using newly developed cyclic testing protocols that enable statistically significant evaluation of four different semiconductors by quantifying both, environmental and operational stress on their performance. It is demonstrated that the structure of the phthalocyanine leads to significant differences in response to bias stress, such as silicon bis(pentafluorophenoxy)phthalocyanine (F₁₀-SiPc) showing a much more air-stable p-type device compared to copper phthalocyanine (CuPc) and bis(pentafluorophenoxy) hexadecafluoro silicon(iv) phthalocyanine  (F₅PhO)₂-F₁₆-SiPc showing much more air-stable n-type performance compared to Copper(II) 1,2,3,4,8,9,10,11,15,16,17,18,22,23,24,25-hexadecafluoro-29H,31H-phthalocyanine (F₁₆-CuPc). Raman microscopy of the films revealed no changes in morphology. The devices are also modeled using the 2D finite-element method, which suggests that most changes in device performance are due to fixed charges at the semiconductor/insulator interface. Overall, OTFT stress testing demonstrates, that important structure property relationships can be established between semiconductor molecular structure and device performance.