Greensolar technologies

Thin film amorphous silicon tandem solar cells

Amorphous silicon solar module technology has its advantage of being simple and low-cost. However, it has a drawback as well, namely its low quality including instability under illumination due to the so-called Staebler-Wronski effect. It has been found that this instability effect depends on the thickness of i-layers, the thinner the i-layer, the more stable the solar cell is. But the thinner the i-layer, the less photon it can absorb resulting in lower current and efficiency. So, here there is a trade-off. Choosing a tandem structure, where there are two p-i-n cells on top of each other, helps to gain on both sides. I-layers may become thinner, thus more stable, but because there are two i-layers, they provide sufficient photon absorption as well.

Thin film micromorph silicon solar cells

Besides its instability as a drawback, the bandgap of amorphous silicon material is not well matched to the solar spectrum. Therefore amorphous silicon solar cells can only convert the energy of photons in the visible light and in the near UV range. If one could use a lower bandgap material as an absorber and active layer in the second part of the tandem cell, the NIR part of the spectrum could be exploited as well. Microcrystalline silicon is such and its bandgap together with amorphous silicon bandgap is an optimal combination for constructing tandem solar cells. Luckily, microcrystalline silicon is quite stable and can be formed from the same raw material as amorphous silicon using a modified and more sophisticated technology. Tandem cells consisting of both amorphous silicon and microcrystalline silicon solar cells are called micromorph silicon solar cells. This type of solar cells has higher effeciency and higher stability relative to amorphous silicon tandem solar cells. However, its production due to the high sophistication is more costly.