In this study, we have examined the correlation between work function (WF) of indium-tin-oxide (ITO) and open-circuit voltage (Voc) 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 p-substituted benzenesulfonyl chlorides with different electron withdrawing terminal groups (C6H5-, Cl- and NO2-) has exploited to change the WF of ITO up to 5.28 eV with NO2-. Chemically modified ITOs and SubPc, ZnPc were used as anode electrode and donor materials, respectively. In order to find the correlation of Voc, 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 Voc was strongly dependent on WF of ITO. However, for ZnPc, the Voc 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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