首页 技术方案 OLED 防护紫外线伤害而延长OLED寿命

防护紫外线伤害而延长OLED寿命

紫外线(UV)光比可见光波长更短且能量更大(如图1所示),众所周知,如果暴露在高强度的紫外线环境中 , 紫外线会对人体造成伤害。 另外还有一些东西也会受到紫外线的伤害,比如OLED显示器中的有机材料。

 

图1 光谱分布图

 
图1 光谱分布图

 

通常会使用紫外线指数(UV index)来定义紫外线的强度,它是衡量特定地点和时间紫外线辐射强度对人体所造成伤害的国际标准。如表1所示。

 

表1 紫外线指数(UV index)

 
UV index Media graphic color Risk of harm from unprotected sun exposure, for the average adult Recommended protection
0 to 2 Green "Low" A UV index reading of 0 to 2 means low danger from the Sun's UV rays for the average person. Wear sunglasses on bright days. If you burn easily, cover up and use broad spectrum SPF 15+ sunscreen. Bright surfaces, sand, water, and snow, will increase UV exposure.
3 to 5 Yellow "Moderate" A UV index reading of 3 to 5 means moderate risk of harm from unprotected sun exposure. Stay in shade near midday when the Sun is strongest. If outdoors, wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.
6 to 7 Orange "High" A UV index reading of 6 to 7 means high risk of harm from unprotected sun exposure. Protection against skin and eye damage is needed. Reduce time in the sun between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.
8 to 10 Red "Very high" A UV index reading of 8 to 10 means very high risk of harm from unprotected sun exposure. Take extra precautions because unprotected skin and eyes will be damaged and can burn quickly. Minimize sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.
11+ Violet "Extreme" A UV index reading of 11 or more means extreme risk of harm from unprotected sun exposure. Take all precautions because unprotected skin and eyes can burn in minutes. Try to avoid sun exposure between 10 a.m. and 4 p.m. If outdoors, seek shade and wear sun-protective clothing, a wide-brimmed hat, and UV-blocking sunglasses. Generously apply broad spectrum SPF 15+ sunscreen every 1.5 hours, even on cloudy days, and after swimming or sweating. Bright surfaces, such as sand, water, and snow, will increase UV exposure.

 

有机材料制成的发光层是OLED显示器发光的关键,但是高强度的UV能量会破坏有机发光层的结构,在这种情况下会影响发光效率,OLED显示器的亮度会下降。为了保护有机材料免受紫外线的伤害,必须尽量减少紫外线波长范围的强度,同时保留可见光范围(400nm~700nm)的强度,采用偏光片是非常有效的解决方案。如图2所示。

In order to protect the organic material from UV damage, we have to minimize the intensity of UV wavelength. Meanwhile, we don’t want to decrease the intensity in the visible light range(400nm~700nm). For this purpose, polarizers are very suitable.

 

图2 偏光片之穿透光谱分布

 
图2 偏光片之穿透光谱分布

 

为了证明偏光片对紫外线的防护能力,设计了一个实验,使用偏光片覆盖OLED面板的一半区域,另一半区域无任何覆盖。 然后将OLED面板放入UV照射腔体,经过UV照射后测量OLED显示屏两个区域的亮度,即可得到OLED面板在UV曝光下的亮度衰减率数据。

根据实验结果,如图3所示。蓝线曲线是偏光片覆盖的区域之OLED光亮度衰减曲线,在承受相当于1 UVI强度的能量照射450小时后,亮度衰减了0.76%;红线曲线是没有任何偏光片覆盖的区域之OLED光亮度衰减曲线,在相同的UV照射时间下,亮度衰减了4.97%。此结果说明有偏光片保护时,可以延缓OLED面板在UV曝光下亮度衰减的效果

 

图3 有含(蓝线)及不含(红线)偏光片覆盖之OLED光亮度衰减曲线

 
图3 有含(蓝线)及不含(红线)偏光片覆盖之OLED光亮度衰减曲线

 

在不同的紫外线强度下,估算OLED 显示器的亮度衰减到 50% 的使用寿命(Life time)。 假设环境条件如下,一年中的每天都是晴天,一天的总紫外线能量相当于暴露于 4 小时正中午紫外线强度。

在这种情况下,在不同紫外线强度水平下曝光的 OLED 显示器的估计寿命,如表2所示。在高紫外线强度环境 (6UVI) 下,覆盖偏光片的OLED使用寿命是未覆盖偏光片OLED的 3 倍。根据结果,说明有偏光片保护 OLED 显示器避免受紫外线照射的能力伤害,进而延长OLED显示器的寿命。

 

表2 有含及不含偏光片覆盖之OLED光亮度衰减50%寿命

 
  Exposure
intensity 
1UVI
+naturally decay
2UVI
+naturally decay
3UVI
+naturally decay
4UVI
+naturally decay
5UVI
+naturally decay
6UVI
+naturally decay

With
polarizer

How long brightness decay to 50% 749 days 680 days 623 days 575 days 533 days 497 days
w/o
polarizer
How long brightness decay to 50% 481 days 338 days 260 days 212 days 179 days 154 days
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