This is an OpenSCAD design of a ring to hold samples for light soaking in a solar simulator. Print and attach sample with binder clips and hold with chemistry clamp as in photo.

This component is part of the Open-source optics project, whose goal is to radically reduce the cost of scientific optical hardware: by the Michigan Tech's Open Sustainability Technology Research Group.
For similar see the Open-Source Lab How to Build Your Own Hardware and Reduce Research Costs