As already claimed, the idea of a concentrator cell is old, also the idea to stack different types of semiconductors to optimize the output.
For that kind of system you need
* A lens (maybe a fresnell-type for easier production?)
* Tracking system
* Direct (!) sunlight
The lens is not complicated as the semiconductors need protection from the environment.
The tracking system is more tricky: Ensure it is always operating, i.e. the mechanical part is ok (also in the winter season). Also, this system may significantly increase the total costs (the lens still needs the size of a conventional system - you want to collect the sunlight!)
Direct sunlight is the problem: At least in middle europe the higher system efficacy is nullified by a significant number of cloudy days.