Valley Photovoltaics and the Search for the Hot Carrier Solar Cell

In order to achieve a hot carrier solar cell, one must: (a) prevent significant energy loss to phonons; and (b) extract primarily the hot carriers. We have recently suggested a new approach to these problems by using metastable upper energy levels to store the photogenerated carriers. A proof of concept cell based upon an InGaAs/InAlAs structure has yielded encouraging results that suggest that valley storage is occurring and yielding a V
_OC
>E
_G
. Current output, however, is restricted apparently due to a barrier between the L valleys in the two materials. New materials may provide the solution to this problem and lead to a new HCSC with greatly enhanced efficiency.