In theory, you could take a box, coat the inside with a mirroring material and have a smallish black object inside. Then cut a hole in one wall. Theoretically, a big part of the light entering the box would (after a few reflections) be absorbed by the object. If the abject is smaller than the hole, we a have a solar concentrator that works without tracking. Of course we loose power to the multiple reflections.
I wonder if anyone went to the trouble and optimised the shape of the box for this purpose.