UV and Solar Panels?

Yes there is a lot more UV on the surface of Mars because we don't have the atmosphere to protect us. However, Mars is a lot farther from the sun than the Earth is. The sunlight in general is a lot dimmer and solar panels don't just respond to UV. They respond to normal light as well. There's also a lot of dust in the atmosphere of Mars which is a major problem with the solar panels on the recent rovers. They get covered in dust and stop working effectively.