Directional dependence of electron blocking in PEDOT:PSS

Abstract The directional dependence of electron blocking by poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is investigated in organic photovoltaic devices. In a conventional OPV architecture we find that a doped interlayer forms between poly(3-hexylthiophene) (P3HT) and the PSS-rich top layer of spin-coated PEDOT:PSS films. In an inverted OPV architecture, we find no mixing between PEDOT:PSS and P3HT, which is due to the lower concentration of PSS in bulk PEDOT:PSS than is found in the PSS-rich top layer. Through electrical measurements of conventional and inverted photovoltaic devices we show that the interlayer is necessary for PEDOT:PSS to be electron blocking. This result implies that PEDOT:PSS is not intrinsically electron blocking and that its directional anisotropy must be considered when comparing the advantages and disadvantages of conventional and inverted architecture photovoltaic devices.