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 In2O3 semiconductors 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 In2O3 TFTs with different annealing temperatures exhibit poor NBIS stability with serious turn-on voltage shift (Delta V-on). After doping with Pr4+/Tb4+, the TFTs show greatly improved NBIS stability. As the annealing temperature increases, the Pr:In2O3 TFTs have poorer NBIS stability (Delta V-on are -3.2, -4.8, and -4.8 V for annealing temperature of 300, 350, and 400 degrees C, respectively), while the Tb:In2O3 TFTs have better NBIS stability (Delta V-on are -3.6, -3.6, and -1.2 V for annealing temperature of 300, 350, and 400 celcius, respectively). Further studies reveal that the improvement of the NBIS stability of the Pr4+/Tb4+:In2O3 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:In2O3 TFTs compared to Pr:In2O3 TFTs is ascribed to the smaller ion radius of Tb4+ 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 Tb4+ to absorb the visible light than the Pr4+.

Automated summary

This study improves the stability of thin-film transistors (TFTs) based on oxide semiconductors by doping them with Pr4+ or Tb4+. It is found that Tb:In2O3 TFTs have better stability compared to Pr:In2O3 TFTs due to the smaller ion radius of Tb4+ and lower energy level.