Electro-optical characterization and analysis of CuPc-based solar cells with high photovoltage

Organic solar cells using the CuPc and PTCBI semiconductor layers were studied. A high open circuit voltage of 1.15 V was obtained in a device with ITO/PEDOT:PSS/CuPc (15 nm)/PTCBI (7 nm)/Al structure. Results were interpreted in terms of a modified CuPc-Al Schottky diode for the thin PTCBI case and a CuPc-PTCBI heterojunction for the thick PTCBI case. Also, the formation of a thin aluminum oxide layer under the aluminum electrode was postulated. This layer has a beneficial aspect wherein shunting losses are reduced and a high photovoltage is enabled. However, it adds greatly to the series resistance to a point where the short circuit current density is reduced. CuPc Schottky diodes with an ITO/PEDOT:PSS/CuPc/Al structure yielded a high V _oc of 900 mV for a CuPc layer of thickness 140 nm. The V _oc increased with increase in CuPc layer thickness.