Introduction 6873 2. Synthesis of Colloidal Quantum Dots 6874 2.1. Solution Synthesis 6874 2.2. III-V Quantum Dots Grown via Vapor Phase Deposition 6877 3. Relaxation Dynamics of Photogenerated Carriers In QDs 6877 3.1. Experimental Determination of Relaxation/ Cooling Dynamics and a Phonon Bottleneck in Quantum Dots 6878 4. Multiple Exciton Generation (MEG) in Quantum Dots 6878 4.1. MEG in Si QDs 6880 5. Quantum Dot Arrays 6881 5.1. MEG in PbSe QD Arrays 6882 6. Applications: Quantum Dot Solar Cells 6884 6.1. Quantum Dot Solar Cell Configurations 6885 6.1.1. Photoelectrodes Composed of Quantum Dot Arrays 6885 6.1.2. Quantum Dot-Sensitized Nanocrystalline TiO 2 Solar Cells 6885 6.1.3. Quantum Dots Dispersed in Organic Semiconductor Polymer Matrices 6885 6.2. Schottky Junction and p-n Junction Solar Cells Based on Films of QD Arrays 6886 7. Conclusion 6887 8. Acknowledgments 6887 9. Note Added after ASAP Publication 6887 10. References 6887

We describe the structural, optical, and electrical properties of films of spin-cast, oleate-capped PbSe nanocrystals that are treated thermally or chemically in solutions of hydrazine, methylamine, or pyridine to produce electronically coupled nanocrystal solids. Postdeposition heat treatments trigger nanocrystal sintering at approximately 200 degrees C, before a substantial fraction of the oleate capping group evaporates or pyrolyzes. The sintered nanocrystal films have a large hole density and are highly conductive. Most of the amine treatments preserve the size of the nanocrystals and remove much of the oleate, decreasing the separation between nanocrystals and yielding conductive films. X-ray scattering, X-ray photoelectron and optical spectroscopy, electron microscopy, and field-effect transistor electrical measurements are used to compare the impact of these chemical treatments. We find that the concentration of amines adsorbed to the NC films is very low in all cases. Treatments in hydrazine in acetonitrile remove only 2-7% of the oleate yet result in high-mobility n-type transistors. In contrast, ethanol-based hydrazine treatments remove 85-90% of the original oleate load. Treatments in pure ethanol strip 20% of the oleate and create conductive p-type transistors. Methylamine- and pyridine-treated films are also p-type. These chemically treated films oxidize rapidly in air to yield, after short air exposures, highly conductive p-type nanocrystal solids. Our results aid in the rational development of solar cells based on colloidal nanocrystal films.