Solution-processed indium-free ZnO/SnO2 bilayer heterostructures as a low-temperature route to high-performance metal oxide thin-film transistors with excellent stabilities

Abstract

The realization of high performance solution-processable metal oxide thin-film transistors (TFTs) with low annealing temperatures remains a challenge in the field of flexible and/or transparent electronics. Indium-based metal oxides are one of the most widely used materials as channel layers of metal oxide TFTs. However, the need for developing indium-free metal oxide materials has become urgent because of the high cost and limited supply of indium. Herein, we report high-performance solution-processed indium-free metal oxide TFTs prepared with low annealing temperatures by introducing ZnO/SnO₂ bilayer heterostructures. After photo- and thermal annealing, ZnO/SnO₂ bilayers form a unique nanostructure composed of three zones: Zn-only, Zn–Sn-mixed, and Sn-rich zones. The resulting ZnO/SnO₂ TFTs exhibit outstanding mobility values as high as 15.4 cm² V⁻¹ s⁻¹ with a low annealing temperature of 300 °C. These values are the highest yet measured among indium-free and solution-processed metal oxide TFTs prepared under similar annealing conditions. The ZnO/SnO₂ TFTs also show remarkable outstanding operational stabilities under various external bias stresses. Their high performances and excellent stabilities can be attributed to the combinational effects of the highly conductive ultrathin Sn-rich channel and balanced carrier concentrations in the Zn–Sn-mixed region. We believe that our work provides a facile route to prepare inexpensive solution-processed electronic devices with earth-abundant materials such as backplane circuits for large-area and flexible displays.