Electronic structure of crystalline copper phthalocyanine

Abstract

The electronic structure of copper-phthalocyanine (CuPc) has been studied both experimentally and theoretically. Experiments have been performed on alpha and beta crystalline phases, using photoemission spectroscopy to probe core levels and valence band spectra. Different photon energies have been used, in order to probe different sample depths. Only minor differences have been observed in the experimental data on the two different phases, except for a small charge effect on the beta phase crystal. First-principles calculations have been performed using the density functional for molecular and three-dimensional periodic solids (Dmol(3)) code on both the single CuPc molecule and the beta phase, allowing the identification of the different atomic and angular contributions to the experimental density of states. In particular, the highest occupied molecular level is mainly due to Cu and N states. The comparison between theoretical data obtained for the CuPc in the beta phase and in the single molecule shows that the interchain interaction between the molecules is negligible, whereas slightly stronger intrachain interactions occur.

Different approaches to adjusting band offsets at intermolecular interfaces

“…For CuPc deposited on Au [23] (Figure 4a), we found qualitative agreement with prior photoemission [8,[22][23][24][25] and inverse photoemission [23,26] experimental data. The positions of the band edges, as determined by photoemission and inverse photoemission at room temperature, do not directly demonstrate that CuPc is strongly more p-type relative to P(VDF-TrFE).…”

“…This is consistent with the fact that CuPc tends to lie flat on metal substrates and stand on oxide surfaces [43]. Regrettably, photoemission features alone are not an effective means of determining orientation and crystal packing of CuPc, although this has been attempted [24], so further measurements such as light incident angle dependent near edge X-ray absorption fine structure measurements are indicated, but as yet, have not been carried out. Strong interactions or charge transfer to CuPc are believed to decrease the size of the HOMO-LUMO gap for CuPc inferred from combined photoemission and inverse photoemission spectra [23].…”

“…Both polyaniline [12,[18][19][20][21] and copper phthalocyanine (CuPc) thin films [8,13,[22][23][24][25][26][27] (schematically illustrated in Figure 5) can be produced by vapor deposition compatible with ultrahigh vacuum photoemission. These films can be grown very thin (100 Å or less) and are free of solvent contamination.…”

Changing band offsets in copper phthalocyanine to copolymer poly(vinylidene fluoride with trifluoroethylene) heterojunctions

“…1͒ and graphite from photoemission and inverse photoemission provides the expected agreement with prior experimental studies 4,5,16,17 and the PM3 semiempirical theoretical calculations ͓Fig. 1 ͑red curve͔͒.…”

“…6͒ ͓Fig. 2͑a͔͒, there is qualitative agreement with prior photoemission [4][5][6]16,17 and inverse photoemission 6,20 experimental data. The positions of the band edges, as determined by photoemission and inverse photoemission at room temperature, suggest that P͑VDF-TrFE͒ is n type, as previously noted, 9 while CuPc is more p type relative to P͑VDF-TrFE͒.…”