Substrate-dependent interface composition and charge transport in films for organic photovoltaics

Abstract

The buried interface composition of polymer-fullerene blends is found by near-edge x-ray absorption fine structure spectroscopy to depend on the surface energy of the substrate upon which they are cast. The interface composition determines the type of charge transport measured with thin film transistors. These results have implications for organic photovoltaics device design and the use of transistors to evaluate bulk mobility in blends.

Photophysical studies of poly-isocyanopeptide based photovoltaic blends

“…We note that, whilst both having a predominantly hydrophilic character, the surface energies of the spectrosil substrates used for optical measurements may be somewhat different from the PEDOT:PSSplanarised substrates used for device work. [15] Whilst the observed top-surface morphologies do not change qualitatively, it is possible that the blend composition and morphology at the substrate is modified, [19,20] with commensurate effects on the orientation of the pery-PIC/PDI chromophores in the interfacial layer.…”

Block copolymer strategies for solar cell technology

“…93 In morphological terms, it is noticeable that there is an influence over the vertical profile of the donor/acceptor composite by the substrate, as would be expected given the different surface energies of the various layers in the device. 29,94,95 FIGURE 3 Some of the common chemical structures recently used in the development of OPVs and mentioned throughout the text.…”

“…OPVs, on the other hand, have higher exciton binding energies and, therefore, excitons must reach a material interface with a lowest unoccupied molecular orbital (LUMO) offset to produce separated electrons and holes. 21 The photovoltaic mechanism in organic devices has been discussed at length in the literature, 19,[22][23][24][25][26][27][28][29] therefore, here, we only briefly outline the process for readers new to the field. Figure 1 shows the individual steps involved in the dominant process that converts light into an electrical current: (i) the incoming photon excites an electron from the HOMO to the LUMO of the donor material to (ii) create an exciton, (iii) which traverses the donor material to a donor-acceptor interface where (iv) the excited electron separates from its bound hole onto the LUMO of the acceptor.…”

Comparison of dimethyl sulfoxide treated highly conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) electrodes for use in indium tin oxide-free organic electronic photovoltaic devices

“…The PEDOT:PSS ADD electrodes have a more hydrophilic surface with a contact angle of 27°whereas PEDOT:PSS IMM electrodes, with a lower concentration of PSS on the surface, have a higher contact angle of 59°. The surface energy of the substrate has been shown to affect the segregation of the subsequently spin-coated polymer blends, with a lower surface energy substrate favouring the lower surface energy blend component [39]. The three PEDOT:PSS electrodes were directly compared to an ITO/PEDOT:PSS HTL reference in OPV devices with the following architecture: electrode/P3HT:PCBM/ BCP/Al.…”