Characterization of high-photovoltage CuPc-based solar cell structures

Organic solar cells of the configuration ITO/PEDOT:PSS/CuPc/PTCBI/Al (Indium Tin Oxide/poly(3,4-ethylenedioxythiophene): polystyrene sulfonic acid/Copper phthalocyanine/3,4,9,10-perylenetetracarboxylic bisbenzimidazole/ Aluminum ) were investigated. A high open circuit voltage (VOC) of 1.15 V was obtained when the PTCBI layer was 7 nm thick. Lower V_oc values were observed for the same structure with silver, copper and gold electrodes instead of aluminum. However, short-circuit current density (JSC) with these electrodes was much higher (4 mA/cm²) than in the case of aluminum (0.12 mA/cm²). Incorporating a 10 nm thick CdS interlayer between PTCBI and aluminum resulted in an increase in current density to 0.3 mA/cm². 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, protective aluminum oxide layer under the aluminum electrode was postulated. For devices with silver, copper and gold electrodes, absence of this protective layer was thought to be the cause of a relatively lower Voc and higher JSC.