Although photodiodes in packages or in chip form are reasonably rugged, avoid touching the cell or package window with bare fingers.
To clean a detector, any dust or loose particles should first be blown away using dry compressed gas. The detector surface or window can then be cleaned by using a lint free swab or lens tissue moistened with isopropyl alcohol and gently wiping the element with a clean, lint free swab or lens tissue. Repeat the wiping procedure for stubborn contamination.
Electronic grade alcohol is preferred for high shunt resistance/low dark current devices without a protective cover.