PbS flexible electronic device: In one embodiment, a flexible PbS electronic device was fabricated in accordance with the following steps. 20 nm thick Au gate electrodes were deposited on a Kapton substrate by evaporation, followed by coating with a 500 nm thick parylene gate dielectric. A monolayer of NCs was formed by dropping a solution of NCs in hexane on an aliquot of acetonitrile. The monolayer is then transferred on to the substrate. The substrate was then immersed in 130 mM (1% w/v) NH4SCN in acetone for less than one minute and washed in acetone in order to perform a solid exchange of ligands as described above. This exchange caused shrinkage of the film, creating void spaces. To overcome the void spaces, three successive layers of NCs were deposited and immersed in SCN. 20 nm thick Au source and drain electrodes were vacuum evaporated on the active layer through a shadow mask. The device may be annealed at 120 C-150 C for about 30 minutes to get better transport. This device exhibited ambipolar behavior as it was not doped by evaporation and thermal diffusion of a dopant metal. All steps were performed under nitrogen atmosphere.