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 In(2)O(3) semiconductors doped with Pr(4+) or Tb(4+), which can effectively improve the NBIS stability. The differences between the Pr(4+)-doped In(2)O(3) (Pr:In(2)O(3)) and Tb(4+)-doped In(2)O(3) (Tb:In(2)O(3)) are investigated in detail. The undoped In(2)O(3) TFTs with different annealing temperatures exhibit poor NBIS stability with serious turn-on voltage shift (ΔV(on)). After doping with Pr(4+)/Tb(4+), the TFTs show greatly improved NBIS stability. As the annealing temperature increases, the Pr:In(2)O(3) TFTs have poorer NBIS stability (ΔV(on) are −3.2, −4.8, and −4.8 V for annealing temperature of 300, 350, and 400 °C, respectively), while the Tb:In(2)O(3) TFTs have better NBIS stability (ΔV(on) are −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 Pr(4+)/Tb(4+):In(2)O(3) TFTs is attributed to the absorption of the illuminated light by the Pr/Tb4f (n)—O2p(6) to Pr/Tb 4f (n+1)—O2p(5) charge 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:In(2)O(3) TFTs compared to Pr:In(2)O(3) TFTs is ascribed to the smaller ion radius of Tb(4+) and the lower energy level of Tb 4f (7) with a isotropic half-full configuration compared to that of Pr 4f (1), which would make it easier for the Tb(4+) to absorb the visible light than the Pr(4+).