I learnt about it in an interesting, and detailed, article in the 22 February issue of The Economist, Solar energy: stacking the deck. Briefly, it explains that by using four layers of different materials, all picking up sunshine at different bandwidths, and with each such stack having a pair of lens at the top to focus the light, much of the sunlight is converted into useful energy.
The normally high costs of the materials are greatly reduced by having tiny stacks, each the size of a pencil point. A solar panel with an area of 125 square metres would have half a million. An ingenious printing technique is used to place the cells on the panel.
The research is attributed to work led by Professor John Rogers of the University of Illinois at Urbana-Champaign. A patent by him and six others for the university, US 7932123, published in 2011, looks very relevant for the stacking concept. It is 80 pages long, of which nearly 60 are drawings. Here are just two of them.
There are (at the time of writing) 12 entries for Semprius on the Espacenet database if US documents are requested. These include Surface-mountable lens cradles and interconnection structures for concentrator type photovoltaic devices and High concentration photovoltaic modules and methods of fabricating the same which both sound very relevant to me.
It all sounds very promising.