This talk will describe our work on the surface chemistry of colloidal semiconductor nanocrystal quantum dots as well as our application of new scanning probe microscopy techniques to the study of interfaces in thin-film polymer solar cells. First, we have fabricated efficient monochromatic light-emitting diodes using CdSe quantum dots as emissive layers. Optimizing particles for these applications requires better understanding and control over colloidal surface chemistry and optical properties. Monitoring the photoluminescence of a CdSe nanocrystal solution during the addition of a surfactant yields an intensity versus concentration curve that looks very similar to a classic Langmuir adsorption isotherm. However, we show that in order to interpret the data from such these experiments one must account for the extremely large number of surface binding sites on the nanocrystals. Furthermore, we use single particle spectroscopy to show that the ensemble photoluminescence is not simply proportional to the fraction of bound ligand sites on the nanocrystal surfaces. Finally, we address issues of polymer mixing and donor/acceptor interfaces that play critical roles in emerging thin-film LEDs and solar cells. We will describe the application of several scanning probe microscopy tools to probe charge generation, transport, and recombination in these heterogeneous mixtures of organic semiconductors.