High-energy solar photons create just one electron/hole-pair in a typical p-n junction cell, although their energies would suffice to produce two or more pairs. Multiple-junction cells alleviate this problem of energy waste. Another possibility is to channel the hot carriers such as to generate secondary pairs. Earlier studies are reviewed, which demonstrated that indeed such multiple generation is observed in carefully produced silicon junction cells. Materials of lower band gaps would be of even greater advantage because more low-energy photons are utilized and the higher photon energies create more than one pair. Search for optimal materials was attempted via the "indirect problem" of finding solutions for a given band structure. Thus far, efficiency enhancement is found to be present but disappointingly small. (C) 2010 Published by Elsevier B.V.