Organic thin-film transistors with improved characteristics using lutetium bisphthalocyanine as a buffer layer

Organic thin-film transistors (OTFTs) with a buffer layer sandwiched between source/drain electrodes and organic semiconductor are demonstrated. An intrinsic molecular semiconductor, Lutetium bisphthalocyanine (LuPc2), is used as the buffer layer due to its high carrier density (¹⁰¹⁶cm3). Compared with conventional OTFTs, the introduction of the buffer layer leads to on-state current increases from 700nA to 2.5μ_{A, field-effect mobility increases from 0.7×10^-2 to 1.58×10^-2cm2/Vs, and threshold voltage downshifts from -21 to -11V for the linear region. The on/off current ratio is improved to a level of ¹⁰⁴. Mechanisms of performance improvement are attributed to include the difference of the Fermi level and interface dipolar between LuPc2} and Au. Our results demonstrate that it is an effective method to improve linear region characteristics by using a molecular semiconductor as the buffer layer.