The indium/galluim puzzle has long been confusing scientists and researchers trying to make solar cells more efficient. The numbers say that the ratio of indium to gallium in thin film solar cells should be optimized at 30:70 but in practice the optimal ratio happens to be the exact opposite of that — 70 to 30. Researchers at the Johannes Gutenberg University Mainz in Germany have just discovered the answer to the puzzle: at low temperatures, the indium and gallium are unable to disperse equally and unequal dispersion causes lower efficiency. They are hoping that this information — coupled with new advances in heat resistant glass — will increase solar efficiency above the current levels.
Researchers know that a theoretical efficiency in solar panels is about 30% but have up until now been unable to come close to that number with thin film solar cells. Thin film solar cells save money as the compound layer needed to gather energy is just micrometers thick and uses a small amount of minerals, but their low efficiency has been a drawback. Scientists have long thought the indium/gallium puzzle was part of the problem, and it turns out they were right. Indium and gallium join copper, selenium and sulfur in thin film solar cells to create an energy grabbing layer in the solar cell. The recent study shows that in contemporary solar panels the layer is applied at lower temperatures because of non-heat resistant glass. At these low temperatures indium and gallium are unable to disperse evenly and at the theoretical ratio of indium and gallium of 30:70 the large deposits of gallium that unevenly form hinder the solar cell’s energy intake.
However, in these current uneven layers, increasing the amount of indium in the cell also increases the energy intake as indium doesn’t hinder the solar absorption, which is why in practice, a ratio of 70:30 has been best. The researchers found that if you layer indium and gallium on to the thin film solar cells at extremely high temperatures, the two compounds form an even layer. In this even layer the theoretical ratio of 30:70 delivers the best solar absorption. Previously the glass used in solar panels was not able to stand high temperatures and caused manufacturers to have to layer the compounds at low temperatures. Due to recent advancements in the science revolving around glass used in thin film solar cells, manufacturers are now able to up the temperature to at least 600 degrees Celsius. Using this glass along with the correct ratio of indium to gallium as well as significantly increasing the temperature during manufacturing will bring thin film solar cell efficiency up about 10%.
Via Science Daily