The stability and performance of N,N'-dioctyl perylene diimide (PDI-C8) and N,N'-ditridecyl perylene diimide (PDI-C13) thin-film transistors (TFTs) are increased using optimized growth rates and sulfur-modified top-contact electrodes. Changing the grain size and the depth of grain boundaries by controlling film growth rate is another way of increasing the air stability of perylene diimides without electron-withdrawing groups. [GRAPHICS]