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 InO semiconductors doped with Pr or Tb, which can effectively improve the NBIS stability. The differences between the Pr-doped InO (Pr:InO) and Tb-doped InO (Tb:InO) are investigated in detail. The undoped InO TFTs with different annealing temperatures exhibit poor NBIS stability with serious turn-on voltage shift (Δ). After doping with Pr/Tb, the TFTs show greatly improved NBIS stability. As the annealing temperature increases, the Pr:InO TFTs have poorer NBIS stability (Δ are -3.2, -4.8, and -4.8 V for annealing temperature of 300, 350, and 400 °C, respectively), while the Tb:InO TFTs have better NBIS stability (Δ 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/Tb:InO TFTs is attributed to the absorption of the illuminated light by the Pr/Tb4-O2 to Pr/Tb 4-O2 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:InO TFTs compared to Pr:InO TFTs is ascribed to the smaller ion radius of Tb and the lower energy level of Tb 4 with a isotropic half-full configuration compared to that of Pr 4, which would make it easier for the Tb to absorb the visible light than the Pr.