The memory characteristics of solution-processed organic field-effect transistors (OFETs) based on polythiophenes with organic floating-gate layers composed of an organic insulator of poly(methylmethacrylate) and a small-molecule semiconductor of TIPS-pentacene have been investigated. The memory characteristics can be improved by addition of a small amount of soluble fullerene derivatives to the floating-gate layer, which helps increase the on- and off-current ratio. Furthermore, programming voltages can be reduced to 20 V by using thin parylene gate insulators as a result of the decrease in the subthreshold swing and the increase in the drain current. We have demonstrated that our OFETs can record images as stored charges by using reflected light from the black and white striped patterns for their applications to printed image sensors.