Influence of metal cathode for organic photovoltaic device performance

Influences of metal electrode on the performance of organic photovoltaic device were studied. An appropriate energy level was set between HOMO of donor material and LUMO of acceptor material used to fabricate device and metals with workfunction above, below and within this appropriate range were selectively chosen to form electron collecting electrode. Metals which can form an Ohmic contact showed enhanced power conversion efficiency, while metals forming a Schottky type contact showed poor power conversion efficiency. Series resistances showed characteristic values for each range. Open circuit voltages were in the same order with power conversion efficiency, showing a dependence on injection barrier at negative electrode contact. The power conversion efficiency of low workfunction metal electrode (i.e. calcium electrode device) was higher than that of gold electrode where the electron extraction is spontaneous process.