Current-voltage characteristics of perylene crystals have been measured at different temperatures both with coplanar Au contacts and in the sandwich configuration in between an indium tin oxide bottom contact and a Au top contact. The voltage and temperature dependences of the current turned out to be very different in coplanar and sandwich structures. A strong increase of the conductivity in coplanar contact structures was observed upon oxygen-plasma treatment, indicating a strong influence of surface states on electronic properties of organic crystals. The effect of crystal-growth conditions on electronic parameters of the crystal is discussed. The obtained experimental data are interpreted in terms of dopant-assisted charge injection across a metal-organics interface. (C) 2005 American Institute of Physics.