Semiconductor Quantum Dots for Applications to Advanced Concepts for Solar Photon Conversion to Electricity and Solar Fuels

There are several approaches to increase the theoretical power conversion efficiency (PCE) of solar cells by using the high photon energies in the solar spectrum more efficiently or by recovering the energy of sub-bandgap photons. For the former, the multi-junction or tandem junction solar cell is the most successful approach which employs multiple p-n junctions of different bandgap (Eg) operating in tandem, where the Eg layers are designed to each absorb a different portion of the total incident sunlight. For an infinite number of junctions in the stack, the PCE reaches 66% at 1-sun intensity. Previous work demonstrates that high PCE is also possible in a single bandgap cell by utilizing the total excess kinetic energy of hot photogenerated carriers in several ways, such as where hot carriers are transported and collected at energy-selective contacts (max PCE = 66%), or by utilizing the excess energy of absorbed photons above the Eg to create additional electron-hole pairs and photocurrent (a process called Multiple Exciton Generation (MEG) in quantized semiconductors and impact ionization in bulk semiconductors.).