system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5:Solar panel losing its efficiency

I read that solar panels loses efficiency eventually. But I can not wrap my head on why it does, considering that there is no moving parts.
gpt
Hey, Ph.D here working on light induced degradation (LID) in solar cells.

Essentially, you need to think of the efficiency of a solar cell as its ability to generate but also collect electrons as useful energy. Now in the body of the solar cell, which we call the bulk, you can get many things that will steal that electron and stop it from being collected. These include metallic impurities (Iron, chromium, copper...etc.), crystallographic defects and usually anything that has a charge that can capture an electron or a hole (which we call charge carriers). The more of these defects you have the lower your effective efficiency.

So what happens out in the field over time? There are many things that can happen that can cause a module to degrade. On the macro level, standard deterioration from corrosion, UV exposure, humidity, etc as mentioned by others in this thread. We also have a few such as PID (potential induced degradation) and LID (Light Induced Degradation). LID for example in monocrystalline solar cells is largely known to be due to the Boron-Oxygen defects. Under sunlight, boron and oxygen can combine together to form a B-O complex, which likes to steal charge carriers and usually results in a drop in efficiency within the first 48 hours. Now this problem has largely been solved. There are a few other known elements that can cause degradation under sunlight, i.e copper (which can form precipitates) and Hydrogen, etc etc..