We have observed very efficient multiple exciton generation (MEG) in PbSe, PbS, PbTe, and Si colloidal nanocrystals (quantum dots (QDs)) at threshold photon energies of 2-3 times the HOMO-LUMO transition. For Si, the first indirect semiconductor QD exhibiting MEG and the most important semiconductor for solar cell applications, QDs with a radius about equal to the exciton Bohr radius (5 nm) show only a small blue shift (weak quantum confinement) but still exhibit efficient MEG.. This has very important implications for QD solar cell applications. Very recently, some controversy has arisen regarding the reproducibility of reported MEG efficiencies in InAs and CdSe QDs. This controversy will be addressed and possible reasons for non-reproducibility of certain QD syntheses and measurement techniques will be discussed. We have studied MEG in close-packed PbSe QD arrays where the QDs are electronically coupled in the films and thus exhibit good carrier mobility. We have demonstrated that the MEG efficiency in such conductive PbSe QD films is comparable to isolated QDs in colloids. This is important since a promising device geometry for MEG solar cells is a 3D QD array forming a film that is the intrinsic region of a p-i-n or metal-i-metal structure; the extended states formed from the electronically coupled QDs allow the delocalized photogenerated carriers to separate, traverse the film, and be collected at the electrical contacts.. Exchanging the bulky capping ligands used in the QD synthesis with shorter molecules after film formation dramatically increases the carrier mobility of QD films by reducing the interdot spacing while retaining well-passivated surfaces. Distinct excitonic features, similar to that in isolated QDs in solution, are preserved in these electronically- coupled arrays. We have developed a simple, all-inorganic metal/QD/metal sandwich solar cell that produces a large short-circuit photocurrent (~20-30 mA/cm2) via a Schottky junction at the negative electrode without the need for sintering, superlattice order or separate phases for electron and hole transport.. The PbSe NC film, deposited via layer-by-layer (LbL) dip coating, yields a solar power conversion efficiency of 2 to 2.5% at AM1.5. Experiments to determine MEG photocurrent quantum yields are in progress.