Unveiling the Mechanics Behind Polyimide's Friction-Greening Phenomenon.

Polyimide (PI) has been widely used as a flexible substrate in the OLED display industry to achieve folding and other functions. However, it has unintended side effects, such as friction-greening, a green screen phenomenon caused by friction after prolonged usage. This is related to drifting TFT characteristics caused by charge accumulating in the PI in combination with the high efficiency of green pixels. In this study, the mechanism of the influence of PI structure on friction-greening was investigated. Increasing the process temperature from 350 °C to 470 °C, the chain segment structure within the PI became more regularized. Thus, the material had higher conductivity and shallower trap energy levels, which was confirmed by X-ray small angle scattering, dielectric, photoluminescence, and other methods. Under prolonged discharge conditions, less charge accumulated within PI, thus effectively mitigating the threshold voltage drift of the thin-film transistor (TFT). These results will contribute to the further optimization of the process and the development of PI materials.