Interfacial chemical and electronic structure of cobalt deposition on 2,7-dioctyl[1]benzothieno[3,2-b]benzothiophene (C8-BTBT)

•Chemical reaction and band bending at the interface are confirmed by the UPS and XPS.•Co atoms mostly accumulate at or near the interface and penetration into sublayer is weak.•The electron and hole barriers are too high and interfacial buffer layer is needed for device design.