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 (Δ V 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 (Δ V 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 (Δ V 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/Tb4 f n -O2 p 6 to Pr/Tb 4 f n+1 -O2 p 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 4 f 7 with a isotropic half-full configuration compared to that of Pr 4 f 1 , which would make it easier for the Tb 4+ to absorb the visible light than the Pr 4+ .