Despite significant interest in hybrid organic/inorganic semiconductor interfaces, little is know... more Despite significant interest in hybrid organic/inorganic semiconductor interfaces, little is known regarding the fate of charge carriers at metal oxide interfaces, particularly on ultrafast time scales. Using core-hole clock spectroscopy, we investigate the ultrafast charge carrier dynamics of conductive ZnO films at a hybrid interface with an organic semiconductor. The adsorption of C60 on the ZnO surface strongly suppresses the ultrafast carrier delocalization and increases the charge carrier residence time from 400 attoseconds to nearly 30 fs. Here, we show that a new hybridized interfacial density of states with substantial molecular character is formed, fundamentally altering the observed carrier dynamics. The remarkable change in the dynamics sheds light on the fate of carriers at hybrid organic/inorganic semiconductor interfaces relevant to organic optoelectronics and provides for the first time an atomistic picture of the electronically perturbed near-interface region of a metal oxide.
Thin films of Spiro-MeOTAD were prepared by evaporation from powder materials (SHT-263, Merck KGa... more Thin films of Spiro-MeOTAD were prepared by evaporation from powder materials (SHT-263, Merck KGaA) using quartz crucible evaporators in a UHV chamber with a base pressure of 10 -9 mbar. The deposition rate of Spiro-MeOTAD was 0.1-0.2 Å/s monitored by the quartz-crystal monitors and the intended total thicknesses were 510 nm. As-received Si(100) wafers (covered with native oxide, SAMCO Inc., 0.013 cm) and thermally evaporated Au (thickness ~ 150 nm) on SiO 2 (native oxide)/Si were used as substrates for the Spiro-MeOTAD evaporation. Combined ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) measurements of the Spiro-MeOTAD(5 nm)/SiO 2 /Si(100) were performed in a homebuilt modular chamber in Princeton University with a base pressures of 10 -9 and 10 -10 mbar in the preparation and analysis chambers, respectively. The resolution of UPS He discharge lamp (He-I=21.2 eV) and double-pass cylinder mirror analyzer was 0.15 eV. The resolution of IPES was 0.45 eV. 1 The photo-current and incident current densities during measurements are limited to 1 nA/mm 2 and 0.1 A/mm 2 for UPS and IPES, respectively. 2 UV and electron induced sample damage was monitored on the sample after taking the measurements at 9 different spots. No radiation induced changes in the UPS and IPES were observed in the time frame of the data acquisition. The common energy scale of UPS and IPES spectra was obtained by calibrating the binding energy (BE) with respect to the Fermi edge (w.r.t. E F ) measured with both techniques on the same Au surface. Additional, in situ electronic characterization of Spiro-MeOTAD(10 nm)/Au/SiO 2 was performed in a modular UHV system (Omicron NanoTechnology
ABSTRACT In this study the properties of organic thin film, transistors (OTFTs) based on perylene... more ABSTRACT In this study the properties of organic thin film, transistors (OTFTs) based on perylene films have been investigated. To tailor the film properties, the dielectric layer on which the perylene films were deposited on was modified by different chemical treatments. Both film properties and the device efficiency have been studied employing a range of techniques including atomic force microscopy, X-ray diffraction and a drop shape analysis for the determination of the surface free energy. A clear correlation between the adhesion energy with the dielectric surface modification is found. The change in adhesion energy influences the thin-film growth on the modified substrate and therefore the film morphology and structure. This in turn has a profound impact on the transistors performance as the charge carrier mobility and the on-to-off current ratio are effected. Hence by tailoring of the dielectric surface for the growth of perylene films, the thin-film transistor performance can be optimized. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Combined photoemission and charge-transport property studies of the organic hole transport materi... more Combined photoemission and charge-transport property studies of the organic hole transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD) under air exposure and controlled environments of O 2 , H 2 O + N 2 , and N 2 (1 atm and under dark conditions) reveal the incorporation of gas molecules causing a decrease in charge mobility. Ultraviolet photoelectron spectroscopy shows the Fermi level shifts toward the highest occupied molecular orbital of spiro-MeOTAD when exposed to air, O 2 , and H 2 O resembling p-type doping. However, no traces of oxidized spiro-MeOTAD + are observed by X-ray photoelectron spectroscopy (XPS) and UV−visible spectroscopy. The charge-transport properties were investigated by fabricating organic field-effect transistors with the 10 nm active layer at the semiconductor−insulator interface exposed to different gases. The hole mobility decreases substantially upon exposure to air, O 2 , and H 2 O. In the case of N 2 , XPS reveals the incorporation of N 2 molecules into the film, but the decrease in the hole mobility is much smaller. SECTION: Energy Conversion and Storage; Energy and Charge Transport
Photovoltaic applications of perovskite semiconductor material systems have generated considerabl... more Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH 3 NH 3 PbI 3 (MAPbI 3), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO 2 appears tolerant to the formation of compensating defect pairs of V I and V MA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide−lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI 3 electronic structure to distributed defects that can significantly transform the electronic density of states only when in high concentrations.
Despite significant interest in hybrid organic/inorganic semiconductor interfaces, little is know... more Despite significant interest in hybrid organic/inorganic semiconductor interfaces, little is known regarding the fate of charge carriers at metal oxide interfaces, particularly on ultrafast time scales. Using core-hole clock spectroscopy, we investigate the ultrafast charge carrier dynamics of conductive ZnO films at a hybrid interface with an organic semiconductor. The adsorption of C60 on the ZnO surface strongly suppresses the ultrafast carrier delocalization and increases the charge carrier residence time from 400 attoseconds to nearly 30 fs. Here, we show that a new hybridized interfacial density of states with substantial molecular character is formed, fundamentally altering the observed carrier dynamics. The remarkable change in the dynamics sheds light on the fate of carriers at hybrid organic/inorganic semiconductor interfaces relevant to organic optoelectronics and provides for the first time an atomistic picture of the electronically perturbed near-interface region of a metal oxide.
Thin films of Spiro-MeOTAD were prepared by evaporation from powder materials (SHT-263, Merck KGa... more Thin films of Spiro-MeOTAD were prepared by evaporation from powder materials (SHT-263, Merck KGaA) using quartz crucible evaporators in a UHV chamber with a base pressure of 10 -9 mbar. The deposition rate of Spiro-MeOTAD was 0.1-0.2 Å/s monitored by the quartz-crystal monitors and the intended total thicknesses were 510 nm. As-received Si(100) wafers (covered with native oxide, SAMCO Inc., 0.013 cm) and thermally evaporated Au (thickness ~ 150 nm) on SiO 2 (native oxide)/Si were used as substrates for the Spiro-MeOTAD evaporation. Combined ultraviolet photoelectron spectroscopy (UPS) and inverse photoemission spectroscopy (IPES) measurements of the Spiro-MeOTAD(5 nm)/SiO 2 /Si(100) were performed in a homebuilt modular chamber in Princeton University with a base pressures of 10 -9 and 10 -10 mbar in the preparation and analysis chambers, respectively. The resolution of UPS He discharge lamp (He-I=21.2 eV) and double-pass cylinder mirror analyzer was 0.15 eV. The resolution of IPES was 0.45 eV. 1 The photo-current and incident current densities during measurements are limited to 1 nA/mm 2 and 0.1 A/mm 2 for UPS and IPES, respectively. 2 UV and electron induced sample damage was monitored on the sample after taking the measurements at 9 different spots. No radiation induced changes in the UPS and IPES were observed in the time frame of the data acquisition. The common energy scale of UPS and IPES spectra was obtained by calibrating the binding energy (BE) with respect to the Fermi edge (w.r.t. E F ) measured with both techniques on the same Au surface. Additional, in situ electronic characterization of Spiro-MeOTAD(10 nm)/Au/SiO 2 was performed in a modular UHV system (Omicron NanoTechnology
ABSTRACT In this study the properties of organic thin film, transistors (OTFTs) based on perylene... more ABSTRACT In this study the properties of organic thin film, transistors (OTFTs) based on perylene films have been investigated. To tailor the film properties, the dielectric layer on which the perylene films were deposited on was modified by different chemical treatments. Both film properties and the device efficiency have been studied employing a range of techniques including atomic force microscopy, X-ray diffraction and a drop shape analysis for the determination of the surface free energy. A clear correlation between the adhesion energy with the dielectric surface modification is found. The change in adhesion energy influences the thin-film growth on the modified substrate and therefore the film morphology and structure. This in turn has a profound impact on the transistors performance as the charge carrier mobility and the on-to-off current ratio are effected. Hence by tailoring of the dielectric surface for the growth of perylene films, the thin-film transistor performance can be optimized. (C) 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
Combined photoemission and charge-transport property studies of the organic hole transport materi... more Combined photoemission and charge-transport property studies of the organic hole transport material 2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene (spiro-MeOTAD) under air exposure and controlled environments of O 2 , H 2 O + N 2 , and N 2 (1 atm and under dark conditions) reveal the incorporation of gas molecules causing a decrease in charge mobility. Ultraviolet photoelectron spectroscopy shows the Fermi level shifts toward the highest occupied molecular orbital of spiro-MeOTAD when exposed to air, O 2 , and H 2 O resembling p-type doping. However, no traces of oxidized spiro-MeOTAD + are observed by X-ray photoelectron spectroscopy (XPS) and UV−visible spectroscopy. The charge-transport properties were investigated by fabricating organic field-effect transistors with the 10 nm active layer at the semiconductor−insulator interface exposed to different gases. The hole mobility decreases substantially upon exposure to air, O 2 , and H 2 O. In the case of N 2 , XPS reveals the incorporation of N 2 molecules into the film, but the decrease in the hole mobility is much smaller. SECTION: Energy Conversion and Storage; Energy and Charge Transport
Photovoltaic applications of perovskite semiconductor material systems have generated considerabl... more Photovoltaic applications of perovskite semiconductor material systems have generated considerable interest in part because of predictions that primary defect energy levels reside outside the bandgap. We present experimental evidence that this enabling material property is present in the halide-lead perovskite, CH 3 NH 3 PbI 3 (MAPbI 3), consistent with theoretical predictions. By performing X-ray photoemission spectroscopy, we induce and track dynamic chemical and electronic transformations in the perovskite. These data show compositional changes that begin immediately with exposure to X-ray irradiation, whereas the predominant electronic structure of the thin film on compact TiO 2 appears tolerant to the formation of compensating defect pairs of V I and V MA and for a large range of I/Pb ratios. Changing film composition is correlated with a shift of the valence-band maximum only as the halide−lead ratio drops below 2.5. This delay is attributed to the invariance of MAPbI 3 electronic structure to distributed defects that can significantly transform the electronic density of states only when in high concentrations.
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Papers by Philip Schulz