The stability of the ITO/CuPc/C-60/Al cells exposed in air without encapsulation is studied. It is found that the performances of the cells will first enhance a little during the first hour after fabrication, and then begin to decline. The reason can be attributed to the appearance of Al2O3 layer at the interface of C-60/Al. The function and mechanism of this Al2O3 layer are similar to a LiF cathode buffer layer. The verification experiments were established and the optimal encapsulation time for ITO/CuPc/C-60/Al cells was demonstrated. The optimal encapsulation time in this work is an hour after removing from the vacuum. (C) 2010 Elsevier B.V. All rights reserved.