The field-effect transistor method is used to study the mobility of charge carriers in layers of lead sulfide nanocrystals with ligands of tetrabutylammonium iodide and 1,2-ethanedithiol used to create solar cells. The difference between the operating of a transistor in ambient air and in an inert atmosphere is demonstrated. It is shown that, in the ambient air, the processes of charging nanocrystals are activated when current flows, and the influence of the polarization of the interface of nanocrystals and the insulator on the measurement of the mobility is analyzed. Different reactions of the layers with ligands to light have been demonstrated, showing a significant oxidation of the surface of nanocrystals treated with 1,2-ethanedithiol.