The Mechanism of the Photostability Enhancement of Thin-Film Transistors Based on Solution-Processed Oxide Semiconductors Doped with Tetravalent Lanthanides

The applications of thin-film transistors (TFTs) based on oxide semiconductors are limited due to instability under negative bias illumination stress (NBIS). Here, we report TFTs based on solution-processed In2O3semiconductors doped with Pr4+or Tb4+, which can effectively improve the NBIS stability. The differences between the Pr4+-doped In2O3(Pr:In2O3) and Tb4+-doped In2O3(Tb:In2O3) are investigated in detail. The undoped In2O3TFTs with different annealing temperatures exhibit poor NBIS stability with serious turn-on voltage shift (ΔVon). After doping with Pr4+/Tb4+, the TFTs show greatly improved NBIS stability. As the annealing temperature increases, the Pr:In2O3TFTs have poorer NBIS stability (ΔVonare −3.2, −4.8, and −4.8 V for annealing temperature of 300, 350, and 400 °C, respectively), while the Tb:In2O3TFTs have better NBIS stability (ΔVonare −3.6, −3.6, and −1.2 V for annealing temperature of 300, 350, and 400 ℃, respectively). Further studies reveal that the improvement of the NBIS stability of the Pr4+/Tb4+:In2O3TFTs is attributed to the absorption of the illuminated light by the Pr/Tb4fn—O2p6to Pr/Tb 4fn+1—O2p5charge transfer (CT) transition and downconversion of the light to nonradiative transition with a relatively short relaxation time compared to the ionization process of the oxygen vacancies. The higher NBIS stability of Tb:In2O3TFTs compared to Pr:In2O3TFTs is ascribed to the smaller ion radius of Tb4+and the lower energy level of Tb 4f7with a isotropic half-full configuration compared to that of Pr 4f1, which would make it easier for the Tb4+to absorb the visible light than the Pr4+.