溶劑於高分子發光二極體元件的三重態能量轉移之影響

Abstract

我們利用Stern-Volmer的實驗去探討溶劑對三重態能量從磷光分子轉移到共軛高分子的影響。比較不同系統在相同溶劑中的Stern-Volmer淬息常數，我們發現，當磷光分子的三重態能階越高，淬息效率也越高。此外，比較Stern-Volmer的淬息常數與理論的擴散控制速率常數，我們發現並不是所有的放熱性的三重態能量轉移都是擴散控制的。在甲苯中，PFam4-FIrpic和PFam4-Ir(mppy)3系統的三重態能量轉移是接近擴散控制的。在鄰二氯苯中，PFam4-FIrpic的三重態能量轉移也是接近擴散控制的。然而，對於PFam4-Ir(mppy)3系統在鄰二氯苯中，和PFam4-Ir(FlPy)2(acac)系統的在甲苯中，其三重態能量轉移都不是擴散控制的。由於鄰二氯苯對於PFam4而言是劣溶劑，所以導致了PFam4的大小分布在鄰二氯苯中比在甲苯來的廣，這也許是造成相同系統在鄰二氯苯中的淬息效率都比在甲苯中來的小的原因。共溶劑(體積比：甲苯比鄰二氯苯等於一比一)的黏度和溶解參數都介於甲苯與鄰二氯苯之間，因此得到的Stern-Volmer淬息常數也在這三種溶劑之間。在元件效率中，若主動層是由溶在鄰二氯苯溶劑所旋轉塗布上的，元件的效率會比較低，我們推測這可能是因為此時PFam4形成β相所導致的。

We used the Stern-Volmer experiment to investigate the solvent effect on the triplet energy transfer from the phosphorescent molecule to the conjugated polymer. From the Stern-Volmer quenching constants for the different systems in the same solvent, it shows that the quenching effect is more efficient when the triplet energy of Ir complex becomes much higher than that of the PFam4. Comparing the Stern-Volmer quenching constants with the theoretical diffusion controlled rate constants, we find that not all exothermic triplet energy transfers are diffusion controlled processes. For the PFam4-FIrpic system and the PFam4-Ir(mppy)3 system in the toluene solutions, the triplet energy transfers are close to diffusion controlled. Similarly, for the PFam4-FIrpic system in the DCB solution, the triplet energy transfer is also close to diffusion controlled. However, for the PFam4-Ir(mppy)3 system in the DCB solution and the PFam4-Ir(FlPy)2(acac) system in the toluene solution, the quenching efficiencies are low. Therefore, neither of them is diffusion controlled. The DCB is the poor solvent for the PFam4. So, the distribution of hydrodynamic diameter of PFam4 in the DCB solution is broader than that in the toluene solution. It may cause that, for the same PFam4-Ir complex system, the quenching efficiency in the DCB solution is lower than that in the toluene solution. Because the viscosity (η) and the solubility parameter (δ) of the cosolvent are between that of the toluene and DCB, the quenching constants in the cosolvent solutions are also between them. The lower efficiency of the device with the emitting layer that was spun cast from the DCB solution may be due to the β-phase conformation of PFam4.