Jacques-E. Moser | Ecole Polytechnique Federale de Lausanne (original) (raw)

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Papers by Jacques-E. Moser

Research paper thumbnail of Synthesis, Characterization, and Photocatalytic Activities of Nanoparticulate N, S-Codoped TiO2 Having Different Surface-to-Volume Ratios

The Journal of Physical Chemistry C, 2010

An efficient, visible light active, N, S-codoped TiO 2-based photocatalyst was prepared by reacti... more An efficient, visible light active, N, S-codoped TiO 2-based photocatalyst was prepared by reacting thiourea with nanoparticulate anatase TiO 2. Commercial anatase powders were manually ground with thiourea and annealed at 400°C in two crucibles with different surface-to-volume ratios (S/V) 20 and 1.5) to prepare two N, S-codoped TiO 2 materials. The differentiated aeration conditions during the catalyst annealing on the crucibles allowed for different amounts of O 2 to reach the catalyst surface. The first material, with S/V) 20, herein referred to as D-TKP 102-A, was clear beige colored. The second material, with S/V) 1.5, herein referred to as D-TKP 102-B, was darker and revealed a markedly lower efficiency in Escherichia coli inactivation. The D-TKP 102-A powder presented visible light absorption due to the nitrogen (N) and sulfur (S) doping. X-ray photoelectron spectroscopy signals for this catalyst were observed for N 1s peaks at binding energies of 399.2 and 400.7 eV due to interstitial N-doping or Ti-ON species. The S 2p were due to SO 4-2 signals with BE >168 eV and signals at 162.8 and 167.2 eV due to anionic and cationic S-doping, respectively. By fast kinetic spectroscopy, the decay of the electron induced by pulsed light at λ) 450 nm (∼8 ns/laser pulse) was followed for the D-TKP 102-A catalyst. Undoped D-TKP 102 catalyst did not promote the electron in the visible range, and consequently no signal decay could be observed in the latter case. Low-temperature electron spin resonance measurements at 8 K provided evidence for electrons trapped in shallow traps, such as oxygen vacancies, V o , induced by N, S doped on D-TKP 102-A. The ESR measurements implementing the reactive scavenging with singlet oxygen scavenger, TMP-OH, revealed the production of singlet oxygen (1 O 2).

Research paper thumbnail of Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells

Journal of the American Chemical Society, Jan 20, 2016

Lead halide perovskites have over the last few years attracted considerable interest as photo abs... more Lead halide perovskites have over the last few years attracted considerable interest as photo absorbers in PV-applications with record efficiencies now reaching 22 %. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-VIS, electroluminescence (EL), photoluminescence (PL), and confocal PL-mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices w...

Research paper thumbnail of Sensitization of fullerenes by covalent attachment of a diketopyrrolopyrrole chromophore

Journal of Materials Chemistry, 2012

In an effort to develop new materials for organic solar cell applications, we have synthesized tr... more In an effort to develop new materials for organic solar cell applications, we have synthesized triads of 3,6-dithien-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione (DTDPP) covalently linked at the nitrogen positions to two [6,6]-phenyl-C 61 -butyric acid ester (PCB) units via alkyl chains of different lengths. We present here the excited-state properties of the compounds in solution, as investigated by (timeresolved) spectroscopy. The absorption spectra of the triads are the composite of the ones recorded with the separate fullerene and DTDPP parent molecules, indicating weak electronic coupling between the sub-units. However, the fluorescence quantum yield drops from 74% in pure DTDPP to <1% in the triads, in both polar o-dichlorobenzene (DCB) and non-polar toluene (TOL). According to the energy levels determined by cyclic voltammetry for the parent compounds, charge separation (CS) or excitation energy transfer (EET) could be responsible for the quenching. However, femtosecondresolved transient absorption (TA) measurements revealed the quenching mechanism to be highly efficient EET from the DTDPP to the PCB moieties. Ultrafast fluorescence spectroscopy showed multiphasic EET dynamics, due to different molecular conformations induced by the flexibility of the alkyl linkers, with time constants ranging from the sub-picosecond to the 100-150 ps scale. The DTDPP chromophore thus acts as a sensitizer (or light-absorbing antenna) to channel light towards the fullerenes, which have low absorbance in the visible range. The ultrafast time scale of the EET leading to fast population of the PCB singlet excited state is particularly interesting for potential use of the systems to increase light harvesting in photovoltaic devices containing fullerenes.

Research paper thumbnail of Synthesis, Characterization, and Photocatalytic Activities of Nanoparticulate N, S-Codoped TiO2 Having Different Surface-to-Volume Ratios

The Journal of Physical Chemistry C, 2010

An efficient, visible light active, N, S-codoped TiO 2-based photocatalyst was prepared by reacti... more An efficient, visible light active, N, S-codoped TiO 2-based photocatalyst was prepared by reacting thiourea with nanoparticulate anatase TiO 2. Commercial anatase powders were manually ground with thiourea and annealed at 400°C in two crucibles with different surface-to-volume ratios (S/V) 20 and 1.5) to prepare two N, S-codoped TiO 2 materials. The differentiated aeration conditions during the catalyst annealing on the crucibles allowed for different amounts of O 2 to reach the catalyst surface. The first material, with S/V) 20, herein referred to as D-TKP 102-A, was clear beige colored. The second material, with S/V) 1.5, herein referred to as D-TKP 102-B, was darker and revealed a markedly lower efficiency in Escherichia coli inactivation. The D-TKP 102-A powder presented visible light absorption due to the nitrogen (N) and sulfur (S) doping. X-ray photoelectron spectroscopy signals for this catalyst were observed for N 1s peaks at binding energies of 399.2 and 400.7 eV due to interstitial N-doping or Ti-ON species. The S 2p were due to SO 4-2 signals with BE >168 eV and signals at 162.8 and 167.2 eV due to anionic and cationic S-doping, respectively. By fast kinetic spectroscopy, the decay of the electron induced by pulsed light at λ) 450 nm (∼8 ns/laser pulse) was followed for the D-TKP 102-A catalyst. Undoped D-TKP 102 catalyst did not promote the electron in the visible range, and consequently no signal decay could be observed in the latter case. Low-temperature electron spin resonance measurements at 8 K provided evidence for electrons trapped in shallow traps, such as oxygen vacancies, V o , induced by N, S doped on D-TKP 102-A. The ESR measurements implementing the reactive scavenging with singlet oxygen scavenger, TMP-OH, revealed the production of singlet oxygen (1 O 2).

Research paper thumbnail of Unreacted PbI2 as a Double-Edged Sword for Enhancing the Performance of Perovskite Solar Cells

Journal of the American Chemical Society, Jan 20, 2016

Lead halide perovskites have over the last few years attracted considerable interest as photo abs... more Lead halide perovskites have over the last few years attracted considerable interest as photo absorbers in PV-applications with record efficiencies now reaching 22 %. It has recently been found that not only the composition but also the precise stoichiometry is important for the device performance. Recent reports have, for example, demonstrated small amount of PbI2 in the perovskite films to be beneficial for the overall performance of both the standard perovskite, CH3NH3PbI3, as well as for the mixed perovskites (CH3NH3)x(CH(NH2)2)(1-x)PbBryI(3-y). In this work a broad range of characterization techniques including: X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), photo electron spectroscopy (PES), transient absorption spectroscopy (TAS), UV-VIS, electroluminescence (EL), photoluminescence (PL), and confocal PL-mapping have been used to further understand the importance of remnant PbI2 in perovskite solar cells. Our best devices w...

Research paper thumbnail of Sensitization of fullerenes by covalent attachment of a diketopyrrolopyrrole chromophore

Journal of Materials Chemistry, 2012

In an effort to develop new materials for organic solar cell applications, we have synthesized tr... more In an effort to develop new materials for organic solar cell applications, we have synthesized triads of 3,6-dithien-2-yl-2,5-dialkylpyrrolo[3,4-c]pyrrole-1,4-dione (DTDPP) covalently linked at the nitrogen positions to two [6,6]-phenyl-C 61 -butyric acid ester (PCB) units via alkyl chains of different lengths. We present here the excited-state properties of the compounds in solution, as investigated by (timeresolved) spectroscopy. The absorption spectra of the triads are the composite of the ones recorded with the separate fullerene and DTDPP parent molecules, indicating weak electronic coupling between the sub-units. However, the fluorescence quantum yield drops from 74% in pure DTDPP to <1% in the triads, in both polar o-dichlorobenzene (DCB) and non-polar toluene (TOL). According to the energy levels determined by cyclic voltammetry for the parent compounds, charge separation (CS) or excitation energy transfer (EET) could be responsible for the quenching. However, femtosecondresolved transient absorption (TA) measurements revealed the quenching mechanism to be highly efficient EET from the DTDPP to the PCB moieties. Ultrafast fluorescence spectroscopy showed multiphasic EET dynamics, due to different molecular conformations induced by the flexibility of the alkyl linkers, with time constants ranging from the sub-picosecond to the 100-150 ps scale. The DTDPP chromophore thus acts as a sensitizer (or light-absorbing antenna) to channel light towards the fullerenes, which have low absorbance in the visible range. The ultrafast time scale of the EET leading to fast population of the PCB singlet excited state is particularly interesting for potential use of the systems to increase light harvesting in photovoltaic devices containing fullerenes.