The Staebler–Wronski Effect (SWE) refers to light-induced
metastable changes in the properties of hydrogenated
amorphous silicon.
The defect density of hydrogenated
amorphous silicon (a-Si:H) increases with light exposure, causing an increase in the
recombination current and reducing the efficiency of the conversion of
sunlight
Sunlight is a portion of the electromagnetic radiation given off by the Sun, in particular infrared, visible, and ultraviolet light. On Earth, sunlight is scattered and filtered through Earth's atmosphere, and is obvious as daylight when t ...
into
electricity
Electricity is the set of physical phenomena associated with the presence and motion of matter that has a property of electric charge. Electricity is related to magnetism, both being part of the phenomenon of electromagnetism, as described ...
.
It was discovered by
David L. Staebler and
Christopher R. Wronski in 1977. They showed that the
dark current and
photoconductivity of hydrogenated
amorphous silicon can be reduced significantly by prolonged illumination with intense light. However, on heating the samples to above 150 °C, they could reverse the effect.
Explanation
Some experimental results
* Photoconductivity and dark conductivity decrease rapidly at first before stabilizing at a lower value.
* Interruptions in the illumination has no effect on the subsequent rate of change. Once the sample is illuminated again, the photoconductivity will drop as though there was no interruption.
Suggested explanations
The exact nature and cause of the Staebler–Wronski effect is still not well known.
Nanocrystalline silicon suffers less from the Staebler–Wronski effect than amorphous silicon, suggesting that the disorder in the amorphous silicon Si network plays a major role. Other properties that could play a role are hydrogen concentration and its complex bonding mechanism, as well as the concentration of impurities.
Historically, the most favored model has been the hydrogen bond switching model.
It proposes that an electron-hole pair formed by the incident light may recombine near a weak Si–Si bond, releasing energy suf