In this study, we have examined the correlation between work function (WF) of indium-tin-oxide (ITO) and open-circuit voltage (V oc ) of heterojunction photovoltaic (PV) cells based on different donor materials. Device configurations of ITO(modified)/SubPc/ C60/BCP/Al and ITO(modified)/ZnPc/C60/BCP/Al were used in this study. Surface modification of ITO electrode through psubstituted benzenesulfonyl chlorides with different electron withdrawing terminal groups (C 6 H 5 -, Cl-and NO 2 -) has exploited to change the WF of ITO up to 5.28 eV with NO 2 -.Chemically modified ITOs and SubPc, ZnPc were used as anode electrode and donor materials, respectively. In order to find the correlation of V oc , two different donor materials with different HOMO levels were used in PV cells. When the SubPc was used as a donor in PV cells, the V oc was strongly dependent on WF of ITO. However, for ZnPc, the V oc was almost independent on WF of ITO due to its low HOMO level and formed ohmic contact at the interface between chemically modified ITO electrodes and ZnPc.

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Organic thin film photovoltaic (PV) cells have attracted attention because of their ease of fabrication and potential for low cost production. In this paper, we study the effects of chemical modification of indium-tin-oxide (ITO) on the performance of organic PV cells. The organic PV cells are fabricated, with the cell configuration of ITO/copper phthalocyanine (CuPc) (20 nm)/fullerene (C60) (40 nm)/Al with and without bathocuproine (BCP) (10 nm) between C60 and Al. By the use of para-substituted benzenesulfonyl chlorides with different terminal groups of H- and Cl-, the energy offset at the ITO/CuPc interface is tuned widely depending upon the interface dipoles and thus the correlation between the change in the ITO work function and the performance of the PV cells by chemical modification is examined.