Solar Cell Spectral Sensitivity

I just came across the book Solar Secrets (2014) by Peter Lindemann. It observes that most solar panels are optimized to perform on bright sunny days whereas they barely perform on cloudy days. This while there are panels that capture light of lower wavelengths and are therefore much less affected by clouds.

The author shows this in the following figure from page 17:

Here it can be seen that Amorphous Silicon (a-Si) solar panels produce energy in the 500 to 700 nm wave length range while Crystalline Silicon (c-Si) mostly produce energy from the 700 to 1100 nm wave length range. a-Si panels even perform well behind glass since the visible light is between 380 to 750 nm.

This range is also reported by Abella et al. (2014):

And a similar range was reported more recently by Fernández-Solas et al. (2021):

From what I can find, it's very difficult to buy a-Si panels. There are some small panels that you can buy meant for traveling, but that's about it. Panasonic used to produce these panels in their Amorton line, but these were discontinued.

In the Netherlands, commonly sold panels are monocrystalline (m-Si), which will only reach about half of the output on cloudy days as can be seen in the figure. The 50% number for reduction in capacity is also reported for cloud cover in Europe by Bamisile et al. (2025).

Given that overcast skies mostly produce light below 750 nm, it seems Perovskite panels could also be a good option. These panels are not (yet) widely for sale and mostly a research project.

Cadmium telluride (CdTe) panels, which seem they should only decline by 20-30% on cloudy days, have been used. To this day, First Solar mainly produces CdTe panels.