Semi-transparent organic solar cells (Photo: KIT/Dominik Landerer)
Imagine the windows at our homes and workplaces generating electricity. That feels futuristic, isn’t it? However, with nearly 7 billion square metres of glass surface only in the United States, solar windows would make a super way to harness the energy from the sun. In many parts of the world, including Australia, silicon solar cells rule the rooftop market.
While solar panels on the rooftops, can have silicon modules that are opaque and bulky; the solar panels for a window need to have a good blend of absorbing light to turn it into electricity and also transmit light through the window. One of the parameters required for the cell is the average visible transmittance (AVT), which is the percentage of visible light hitting the window and travelling through to appear on the other side. Scientists are trying to find a good medium which has a good balance between high AVT and high electrical efficiency.
It is reported that an AVT of around 25% would be considered as a benchmark for solar windows. And, electrical power is dependent on two factors, the current and the voltage. According to sources, when scientists tried to focus on increasing the voltage, a careful selection of new organic absorber materials that would produce a high voltage in non-transparent cells was selected. It was found that when placed in a semitransparent solar cell, the voltage was high and also achieved high efficiency.
Another aspect of semitransparent solar cells is to measure the colour-rendering index (CRI). It was reported that by changing the thickness of the absorbing layer, the ability to depict colours accurately and also affect the electrical power produced could be changed. A prospective approach to exceptional CRIs was to replace the organic absorber material that would absorb energy from the sun outside the visible range. However, this is said to limit the efficiency of the cells that can be achieved and limiting the amount of power from the sun to be converted to electricity.