Transport and optical gaps and energy band alignment at organic-inorganic interfaces

Abstract

Evans, D. A., Vearey-Roberts, A. R., Roberts, O. R., Williams, G. T., Cooil, S. P., Langstaff, D. P., Cabailh, G., McGovern, I. T., Goss, J. P. (2013). Transport and optical gaps and energy band alignment at organic-inorganic interfaces. Journal of Applied Physics, 114 (12), [123701]The transport and optical band gaps for the organic semiconductor tin (II) phthalocyanine (SnPc) and the complete energy band profiles have been determined for organic-inorganic interfaces between SnPc and III-V semiconductors. High throughput measurement of interface energetics over timescales comparable to the growth rates was enabled using in situ and real-time photoelectron spectroscopy combined with Organic Molecular Beam Deposition. Energy band alignment at SnPc interfaces with GaAs, GaP, and InP yields interface dipoles varying from -0.08 (GaP) to -0.83 eV (GaAs). Optical and transport gaps for SnPc and CuPc were determined from photoelectron spectroscopy and from optical absorption using spectroscopic ellipsometry to complete the energy band profiles. For SnPc, the difference in energy between the optical and transport gaps indicates an exciton binding energy of (0.6 +- 0.3) eV.publishersversionPeer reviewe

Determination of Energy Level Alignment within an Energy Cascade Organic Solar Cell

“…The SubPc and SubNc C 1s core level spectra (Figure ) exhibit the C–C and C–N components in expected ratios of ∼3:1 and ∼5:1, respectively. Other components that appear at higher binding energies have been associated with π → π* shake-up satellites, whereby the photoemitted electron undergoes energy losses to excitations of electrons across the gap. , …”

Molecular spectroscopy in a solid-state device

“…13,14 In addition, the optical gap, commonly measured by ultravioletvisible spectroscopy (UV-VIS), is different from the transport gap due to the strong exciton binding energy of molecules. 7,13,[15][16][17] Besides, in the case of some organic semiconductors such as C 60 fullerenes, the optical transition associated with the transport states may be symmetry forbidden, which leads to UV-VIS possibly measuring higher onset energies. Finally, the interface gap, obtained by a combination of different surface-sensitive techniques, typically ultraviolet photoemission spectroscopy (UPS) and inverse photoemission spectroscopy (IPES), [18][19][20] can be used to estimate the transport gap, but under the careful consideration of different limiting factors, such as the low resolution of IPES (0.4 eV), the probing depth at the organic-vacuum interface and other surface dependent parameters like roughness.…”

“…The difference detected in the transport gap between C 60 and C 70 proves the sensitivity of i-MOS. The carrier transport gap is a key parameter for many (opto)electronic applications [1][2][3][4][5][6]39 and there are currently several other techniques routinely used to approach this quantity indirectly, 7 including electrochemical spectroscopy, 13,14 ultraviolet-visible spectroscopy (UV-VIS), [15][16][17] ultraviolet photoemission spectroscopy (UPS), inverse photoemission spectroscopy (IPES), [18][19][20]40 and single-molecule scanning tunnelling spectroscopy. 8,10 ESI, † Table S2 compares the E G of C 60 on gold extracted by several different methods.…”