Institute of Lighting and Energy Photonics, National Chiao Tung University, Tainan 71150, Taiwan.
Phys Chem Chem Phys. 2018 Jul 11;20(27):18226-18232. doi: 10.1039/c8cp03008a.
Solid-state white light-emitting electrochemical cells (LECs) are potential candidates in solid-state lighting due to their promising advantages of simple device structure, low-voltage operation and compatibility with inert cathode metals. Adjusting the correlated color temperature (CCT) of background illumination is highly desired for modern smart lighting systems. In this work, a novel technique to tune the CCT of electroluminescence (EL) from white LECs is proposed. Color tuning is based on adjusting the applied voltage pulse period on the host-guest white LECs and the working mechanism is illustrated. A shorter voltage pulse period is insufficient to completely charge the capacitive LEC device and thus the effective voltage applied on the device is lower. Since the host-guest energy level offsets favor carrier trapping, a lower effective applied voltage results in a more pronounced guest emission, rendering redder white EL with a lower CCT. On the other hand, a longer voltage pulse period facilitates more complete charging and the effective voltage applied on the white LEC is higher. A higher bias facilitates direct exciton formation on the host molecule and subsequent partial host-guest energy transfer generates bluer white EL with a higher CCT. By tuning the voltage pulse period from 0.2 to 20 ms, the CCT of EL resulting from white LECs ranges from 2482 to 5723 K. The CCT tuning range is sufficient for general lighting applications. In contrast to color tuning of white LECs under constant-voltage driving, in which >10× brightness enhancement is accompanied by higher-CCT white EL, the discharging half-period in pulse-voltage driving provides relaxation time to turn off the device and reduces the average brightness of the white LECs driven under a longer voltage pulse period. Therefore, similar brightness can be achieved for white EL with different CCTs. No additional optical filtering device is needed for this novel color tuning technique and it has potential for use in solid-state lighting.
基于主体-客体型白色有机电致发光电化学池（LEC）的固态白光发光器件由于其具有简单的器件结构、低压驱动和与惰性阴极金属兼容等优点，在固态照明领域具有很大的应用潜力。现代智能照明系统对背景照明的相关色温（CCT）的调节提出了很高的要求。本工作提出了一种新颖的调节主体-客体型白色 LEC 电致发光（EL）色温的技术。通过调节主体-客体白色 LEC 的外加电压脉冲周期来实现颜色调谐，说明了其工作机制。较短的电压脉冲周期不足以完全给电容型 LEC 器件充电，从而降低了器件上的有效电压。由于主体-客体能级偏移有利于载流子捕获，较低的有效施加电压会导致客体发射更明显，从而使白色 EL 呈现出更红的颜色和更低的 CCT。另一方面，较长的电压脉冲周期有利于更完全的充电，施加在白色 LEC 上的有效电压更高。较高的偏压有利于在主体分子上直接形成激子，随后部分主体-客体能量转移会产生更高 CCT 的更蓝的白色 EL。通过将电压脉冲周期从 0.2 到 20 毫秒进行调谐，白色 LEC 产生的 EL 的 CCT 范围为 2482 到 5723 K。该 CCT 调谐范围足以满足一般照明应用的要求。与在恒压驱动下的白色 LEC 的颜色调谐相比，在脉冲电压驱动下，调谐范围为 >10×的亮度增强伴随着更高 CCT 的白色 EL，放电半周期为关断器件提供了弛豫时间，并降低了在较长电压脉冲周期下驱动的白色 LEC 的平均亮度。因此，不同 CCT 的白色 EL 可以实现相同的亮度。这种新颖的颜色调谐技术不需要额外的光学滤波装置，在固态照明中有很大的应用潜力。
