ABSTRACT
The two most important factors that determine the cost of delivered photovoltaic (PV) power are conversion efficiency and the initial cost per unit area of the PV system. To achieve very low cost PV power (a few US cents/kWh) and, hence, introduce PV power on a massive scale, it is necessary to develop cells that either have ultra-high conversion efficiency (50-60%) with moderate cost (US$100-150 m−2) or moderate efficiency (about 10%) compensated by ultralow cost (<US$2 m−2). We have been investigating the possibility of achieving ultra-high conversion efficiency in single bandgap cells by utilizing high energy electrons (termed hot electrons and created by absorption of solar photons larger than the bandgap) before these high energy electrons convert their excess kinetic energy (equal to the difference between the photogenerated electron energy and the conduction band energy) to heat through phonon emission. The formation of discrete quantized levels in semiconductor quantum dots affects the relaxation dynamics of high energy electrons and holes and could enhance the conversion efficiency by allowing electrical free energy to be extracted from the energetic electrons and/or holes before they relax to their lowest electronic state and produce heat.
