Semiconductor nanoparticles: Synthesis, ultra-fast time-resolved spectroscopy, multiple exciton generation, and applications in solar cells

In this thesis, I describe basic research done to understand the synthesis, optical properties, photophysics, and applications to solar photon conversion of semiconductor nanoparticles, including quantum dots (QDs) and quantum rods (QRs). We intensively studied hot carrier (exciton) cooling dynamics and multi-exciton (carrier) generation (MEG); size dependent absorption properties were quantitatively studied, including absorption cross-section, oscillator strength and radiative decay lifetime. Also studied are nanoparticle shape-control synthesis and charge transfer dynamics in InP/Au hybrid nano structures.; Carrier cooling dynamics and MEG studies are partly motivated by QD solar cell applications. One main process limiting the conversion efficiency of conventional solar cells is the loss of excess kinetic energy of photogenerated supra-energy gap carriers to heat via phonon emission. Two proposed ways to utilize this kinetic energy are: (1) achieve higher photovoltage by using hot carriers before they cool down to the bottom of their respective energy bands, and (2) achieve higher photocurrent via MEG, a process where more than one electron-hole pair (exciton) is generated by a single absorbed photon.; We also constructed and characterized different kinds of QD solar cells to test the applications of QDs in solar photon conversion devices.