Pathways to hot carrier solar cells

Hot carrier solar cells (HCSCs) were first proposed many decades ago. Over the intervening years, there has been a continuing quest to create these cells that hold promise to shatter the Shockley-Queisser efficiency limit on single-junction solar cells. While there have been many positive and suggestive results in recent years, there remains no true operational HCSC. There are perhaps many reasons for this state. Here, many of the requirements for achieving such an HCSC will be discussed and some approaches will be modernized in terms of their science. Valley photovoltaics, in which carriers are transferred to higher-lying valleys of the conduction band will be described and the recent progress is discussed.