新型共轭聚合物PFO-BT15发光二极管的电老化研究

Study on Electro-Degradation of New Conjugated Polymer PFO-BT15 Light Emitting Diodes

PFO-BT15是一种电致发光中心波长为550 nm的新型共轭高分子聚合物材料,将其制成发光二极管器件,结构为ITO玻璃/聚合物PEDOT(120nm)/有机聚合物PFO-BT15(80nm)/Ba(4nm)/Al(200nm),用环氧树脂对阴极侧进行了封装,以减少氧气和水分的进入,从而影响器件的发光性能。在室温环境下对同样的器件进行不同电流密度的电老化处理,记录器件的电流电压曲线,再对老化的样品做电致发光和喇曼光谱测试。实验发现:一方面,通过器件恒定电流的大小影响器件的电压变化速度;另一方面,器件经过一定长时间的电老化,电致发光中心波长变化较小。通过啦曼光谱的测试,推断是因为PEDOT阳极的破损导致了器件的最终发光失败,而器件发光层材料的结构保持相对稳定,说明这种结构的聚合物有着相对稳定的光电性能,对于提高材料发光的稳定性提供了有价值的信息,有助于其他高效发光材料的合成以及稳定性的提高。

In the present paper electroluminescence spectrum and Raman spectrum were used to study electro-degradation of polymer light emitting devices （PLEDs） of PFO-BT15, a new and high-efficiency emitting polymer synthesized by the institute of polymer optoelectronic material ＆ devices（IPOM） in South China University of Technology. The PLEDs with a configuration of ITO glass/PEDOT（120 nm）/PFO-BT15（80 nm）/Ba（4 nm）/Al（200 nm） emitted green light at 550 nm when 5 V dc voltage was applied. Three of those devices were used to study the electro-degradation mechanism of PLEDs. Device A was deposited in vacuum box in dark room to keep sample fresh; Device B was first lighted with current of 1 mA · 0. 25 cm^-2 for 200 minutes, then with current of 5 mA · 0. 25 cm^-2 for 60 minutes, finally with current of 10 mA · 0.25 cm^-2 for 40 minutes; Device C was lighted with current of 20 mA · 0. 25 cm^-2 until the electrol failure. Our experimental results indicate that the degradation speeds highly depend on the current through the devices. The stressed devices show the decrease in electroluminescence efficiency. However, the luminescence spectrum of the stressed device did not change compared with the fresh device, which suggest that the structure of the luminescent polymer did not change with the electro-stress. Raman spectrum was employed to probe the structure changes of the materials used in the device. We found that the PEDOT Raman peak disappeared and the PFO-BT15 Raman peak still existed in electro-stress device. The results confirmed that it was the breakage of the PEDOT layer instead of degradation of emitting polymer, that led to the final failure of the PLEDs device. This work gives some valuable information for the design and development of highly stable organic light-emitting device.