NREL Test Improves Moisture Barriers
The National Renewable Energy Laboratory (NREL) has developed a test that can detect minute amounts of moisture that may have penetrated a transparent film barrier needed to preserve the workings of electronic devices.
Humidity, water spills, or rainfall ruin cell phones, LED displays, TVs, and solar photovoltaic panels.
The lab developed the Electric Calcium Test, or e-Ca, which measures corrosion from water using calcium.
Durability standards for PV modules call for tests lasting 1,000 hours in damp heat conditions. The e-Ca method is 100 to 1,000 times more sensitive than other commercial tests designed to detect small amounts of moisture. NREL’s test can detect down to one ten-millionth of a gram of water per square meter per day. And it has 15 times greater throughput than the best commercial methods on the market today.
With the organic light-emitting diode (OLED) market poised to explode — from $4.9 billion in 2012 for OLED displays to an expected $26 billion by 2018, the e-Ca arrives at a critical time.
The method uses low-cost test cards with calcium metal traces that serve as moisture detectors. Any water vapor that passes through the barrier film reacts with the conductive calcium and forms resistive calcium hydroxide. The test cards are made in large batches in a moisture-free environment. When a barrier is ready to measure, it is sealed on one side of a metal donut-shaped ‘spacer’ element with the test card sealed to the other side.
A good climate for testing is 113 degrees Fahrenheit and 85 percent humidity, a condition hotter and wetter than even Bangkok, Thailand, on a miserable day. Testing in conditions beyond anything likely to be found in nature allows the test to be completed in less time. Another useful climate for testing is 85 percent humidity and 185 degrees Fahrenheit and is a required reliability metric for PV manufacturing.
NREL photo: Dennis Schroeder
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