Multimode Operation of Organic-Inorganic Hybrid Thin-Film Transistors Based on Solution-Processed Indium Oxide Films

Solution-processed metal oxide (MO) thin films have been extensively studied for use in thin-film transistors (TFTs) due to their high optical transparency, simplicity of fabrication methods, and high electron mobility. Here, we report, for the first time, the improvement of the electronic properties of solution-processed indium oxide (InO) films by the subsequent addition of an organic p-type semiconductor material, here 6,13-bis(triisopropylsilylethynyl)pentacene (TIPS-pentacene), yielding organic-inorganic hybrid TFTs. The addition of TIPS-pentacene not only improves the electron mobility by enhancing the charge carrier percolation pathways but also improves the electronic and temporal stability of the I_DS(V_G) characteristics as well as reduces the number of required spin-coating steps of the InO precursor solution. Very interestingly, the introduction of 10 nm TIPS-pentacene films on top of 15 nm InO layers allows the fabrication of either enhancement- or depletion-mode devices with only minimal changes to the fabrication process. Specifically, we find that when the TIPS-pentacene layer is added on top of the source/drain electrodes, resulting in devices with embedded source/drain electrodes [embedded electrode TFTs (EETFTs)], the devices exhibit an enhancement-mode behavior with an average mobility (μ) of 6.4 cm² V^-1 s^-1, a source-drain current ratio (I_on/I_off) of around 10⁵, and a near-zero threshold voltage (V_TH). When on the other hand the TIPS-pentacene layer is added before the source-drain electrodes, i.e., in top-contact electrode TFTs (TCETFTs), a very clear depletion mode behavior is observed with an average μ of 6.3 cm² V^-1 s^-1, an I_on/I_off ratio of over 10⁵, and a V_TH of -80.3 V. Furthermore, a logic inverter is fabricated combining the enhancement (EETFTs)- and depletion (TCETFTs)-mode transistors, which shows a potential for the construction of organic-inorganic hybrid electronics and circuits.