Significant Improvement of Organic Thin-Film Transistor Mobility Utilizing an Organic Heterojunction Buffer Layer

High-mobility vanadyl phthalocyanine (VOPc)/5,5"'−bis(4-fluorophenyl)-2,2':5',2":5",2"'−quaterthiophene (F2-P4T) thin-film transistors are demonstrated by employing a copper hexadecafluorophthalocyanine (F₁₆CuPc)/copper phthalocyanine (CuPc) heterojunction unit, which are fabricated at different substrate temperatures, as a buffer layer. The highest mobility of 4.08 cm²/Vs is achieved using a F₁₆CuPc/CuPc organic heterojunction buffer layer fabricated at high substrate temperature. Compared with the random small grain-like morphology of the room-temperature buffer layer, the high-temperature organic heterojunction presents a large-sized fiber-like film morphology, resulting in an enhanced conductivity. Thus the contact resistance of the transistor is significantly reduced and an obvious improvement in device mobility is obtained.