Energy level alignments at poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] on metal and polymer interfaces

Energy level alignments of poly[N-9′′-hepta-decanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT) cast on top of Au and poly(3,4-ethylenedioxythiophene):poly(styrene sulfonic acid) (PEDOT:PSS) were investigated using ultraviolet and X-ray photoelectron spectroscopy (UPS and XPS) as a function of the concentration of PCDTBT solutions. Although UPS data show similar work functions for Au and PEDOT:PSS, the hole transport barrier (φh) at the PCDTBT/PEDOT:PSS interface is clearly smaller than that at the PCDTBT/Au interface. The XPS spectra show that energy level relaxation occurs at the interface between PCDTBT and electrodes.