Utilization of copper phthalocyanine and bathocuproine as an electron transport layer in photovoltaic cells with copper phthalocyanine/buckminsterfullerene heterojunctions: Thickness effects on photovoltaic performances

In this work, copper phthalocyanine (CuPc) and bathocuproine (BCP) were used as electron transport layers (ETL) in organic photovoltaic (PV) cells with a structure of indium-tin-oxide/CuPc/C60/ ETL/Al. It was found that PV performance was sensitive to the ETL thickness. A complete coverage of ETL on the C60 film was essential to avoid an insulative C60/Al contact. ETL thickness of 6 nm resulted in optimal PV performance. The PV cells with BCP layers of 2-10 nm demonstrated good PV performance due to efficient electron transport from C60 to Al cathode. Similar result was obtained from the devices with CuPc ETL. However, thicker ETL resulted in considerable lose in PV performance. In both cases, different mechanisms responsible for the dependence of PV performance on ETL thickness are discussed.