Extensive literature and publications on intermediate band solar cells (IBSCs) are reviewed. A
detailed discussion is given on the thermodynamics of solar energy conversion in IBSCs, the device
physics, and the carrier dynamics processes with a particular emphasis on the two-step inter-subband
absorption/recombination processes that are of paramount importance in a successful implementation
high-efficiency IBSC. The experimental solar cell performance is further discussed, which has been
recently demonstrated by using highly mismatched alloys and high-density quantum dot arrays and
superlattice. IBSCs having widely different structures, materials, and spectral responses are also
covered, as is the optimization of device parameters to achieve maximum performance.