Towards a single-junction non-concentrator metal halide perovskite hot carrier solar cell: review of current gaps and opportunities in understanding slow hot carrier cooling
The photovoltaic solar cell is a mature technology, with silicon-based technologies deployed at scale, yet current technologies are limited by the Shockley-Queisser thermodynamic limit, known since the early 1960s. The single-junction non-concentrator hot carrier solar cell operating at ambient temperature - with its theoretically predicted ultimate power conversion efficiency limit of nearly 70% that is twice the Shockley-Queisser limit and is higher than what can be achieved with even n=6 multijunction solar cells - has remained an elusive yet hot research target since the early 1980s. Metal halide perovskite semiconductors were discovered in the late 1970s and photovoltaic applications have been intensively researched and developed since the early 2010s. Current technology development of perovskite solar cells is heavily motivated by their expected cheap processing costs relative to other Shockley-Queisser limited technologies. History has shown that very few absorber materials develop into viable solar cell technologies, and it has been recognized that given the declining costs of silicon-based technologies, a new material must offer potential for both lower cost and higher efficiencies than the Shockley-Queisser limit. Slow cooling of photocarriers with energy in excess of the band edges (hot carriers), which is the first prerequisite of a solar absorbing material for building a hot carrier solar cell technology, has been reported in perovskites since the 2010s. The goal of this review is to illuminate the path towards a single-junction perovskite hot carrier solar cell technology by emphasizing uncertainties in understanding slow hot carrier cooling and recommending approaches to resolve them.