Hi there, it is commonly accepted that the lifespan of crystalline silicon solar cells is about 20-30years. And they define the lifespan as when the solar cells efficiency drop to about lower than 10%. However, what are the possible reasons for the degradation? I can only find research papers on the efficiency drop in several months, which may be related to some fundamental defaults in the materials. However, seems that no group studies the long-term degradation. Some suggested reasons like the glass covering the solar cells becomes dirty after years, etc. And I found another research work where the group performed some treatment on the old silicon solar cells (basically cleaning it with some acids and alkalis). They then claimed that the silicon wafer can perform like a brand-new one and be used again in making new cells. If that's the case, that means the silicon part shouldn't change too much after years. That's why I am so curious about why there is such a great efficiency drop.