Electronic structure and carrier transport at laminated polymer homojunctions

Soft contact lamination, whereby films prepared separately from solution are brought into contact to form a single device, was used here to form homojunctions comprising two identical layers of poly(3-hexylthiophene) (P3HT) or two layers of poly[(9,9-dioctylfluorenyl-2,7-diyl)-co-(1,4-benzo-{2,1′-3}-thiadiazole)] (F8BT). Using ultraviolet photoemission spectroscopy (UPS), Kelvin Probe Force Microscopy (KPFM), and current–voltage (I–V) measurements, the electronic structure of, and carrier transport across, these homojunctions were investigated. UPS and KPFM show that lamination does not introduce any significant offset in the molecular levels across the interface. The I–V characteristics confirm this result by showing that transport across the film is largely unaffected by the presence of the laminated interface. This important result means that lamination could become a versatile tool for constructing multi-layer polymer devices.

Graphical abstractFigure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Homojunctions of P3HT and F8BT were formed by soft-contact lamination. ► UPS and KPFM measurements were performed to look at interfacial energy alignment. ► I–V measurements compared single-layer with equivalent laminated films. ► The interfaces were found to be electronically and electrically transparent.