Optical studies on CuPc/C60 heterojunction layered stack for solar cell applications

Interfacial properties of CuPc and C₆₀ based donor/acceptor heterojunction stack was studied using ellipsometric technique. Planar heterojunction and hybrid planar mixed heterojunction layered stacks were prepared on Si substrates. The ellipsometric analyses were performed by considering various stack models including an abrupt interface between the active layer, a gradient in composition of the active layers, and the formation of an interfacial blend layer between the active layers. The results indicate that CuPc/C₆₀ interface of planar heterojunction stack is not abrupt due to the presence of surface nano-crystalline grains over the CuPc layer. The stack model incorporating an interfacial blend layer is modeled using the optical constants of active layers. For hybrid planar mixed heterojunction stack, an abrupt blend layer is formed between the CuPc and C₆₀ layers without a gradient in composition of CuPc and C₆₀ molecular entities. Results obtained from the ellipsometric analyses of the interfacial layer is important for understanding the device performance of CuPc and C₆₀ based organic solar cells.