- A unique window coating technique can improve the energy efficiency of an average household.
- The semitransparent photovoltaics are lightweight and colorful films capable of turning windows into heat insulators and electricity generators.
The trend of environment-friendly building, often referred as green building, has increased the popularity of advanced window coatings that keeps cooling or heating costs down by blocking out unnecessary radiation of sunlight.
The green building practice complements the traditional building design concerns of utility, durability, economy and comfort. They have inspired engineers and researchers to develop thin, see-through solar cells that could transform windows into small electricity generators.
Wouldn’t it be incredible if these two features could be combined into one window-compatible material? Now, a team of material engineers in China has accomplished the same. They have built a unique coating technique to improve the energy efficiency of an average household.
Semitransparent Organic Photovoltaics
Commercial heat-control window sheets are made of silicon photovoltaics, which are applied to the glass window’s exterior or interior to decrease the amount of visible, ultraviolet and infrared light from sunlight. However, they don’t yield great performance due to their heaviness and dull appearance.
Instead of just applying the window coating with transparent solar cells, the scientists built semitransparent photovoltaics: they are light and colorful films capable of turning windows into heat insulators and electricity generators.
They further introduced distributed Bragg reflector on the top of the silicon sheet to selectively reflect the near-infrared light while maintaining decent transparency for the visible wavelengths. This maximizes the heat insulation without sacrificing the electricity-generation and optical properties of organic photovoltaics.
Reference: ScienceDirect | doi:10.1016/j.joule.2018.06.006
It filters out the infrared wavelengths (responsible for heating), while letting visible light through and harvesting energy from near-infrared rays coming from the Sun.
Multifunctional semitransparent organic photovoltaics
The semitransparent organic photovoltaics are capable of generating more than 6 percent power conversion efficiency with 25 percent of high visible light transmission, and over 80 percent of infrared radiation rejection rate.
According to the researchers, installing windows outfitted with dual heat-insulating and electricity-producing properties could lower an average household’s dependence on electricity sources by more than 50 percent.
The researchers also demonstrated that these organic photovoltaics can be fabricated on thin plastic substrates like polyethylene naphthalate. Compared to glass-based photovoltaics, naphthalate-based flexible devices exhibit a reduced Fill Factor value due to lesser transmittance and higher sheet resistance of polyethylene naphthalate substrates. However, the power conversion efficiency and average visible transmittance were still maintained at 6 percent and 23 percent.
The efficiency can be further improved by using the best organic photovoltaics available. These window coating materials are still in their infancy, but the researchers believe that it will soon open new doors for a variety of applications.