Post-deposition annealing and interfacial atomic layer deposition buffer layers of Sb2Se3/CdS stacks for reduced interface recombination and increased open-circuit voltages

in Progress in Photovoltaics (2022)

Elucidating the growth mechanism of ZnO films by atomic layer deposition with oxygen gas via isotopic tracking

in JOURNAL OF MATERIALS CHEMISTRY C (2021), 9(12), 4307-4315

The growth process of zinc oxide (ZnO) thin films by atomic layer deposition (ALD) accompanied by the presence of oxygen gas pulsing is investigated by means of the isotopic tracking of oxygen O-18 from ... [more ▼]

The growth process of zinc oxide (ZnO) thin films by atomic layer deposition (ALD) accompanied by the presence of oxygen gas pulsing is investigated by means of the isotopic tracking of oxygen O-18 from the water precursor and oxygen O-16 from the gas. In a previous study [T. Nguyen et al., Results Mater., 2020, 6, 100088, DOI: 10.1016/j.rinma.2020.100088], by means of structural, electrical, and optical characterizations, we identified key growth parameters of this unusual ALD process. Unexpectedly, the influence of molecular oxygen on the crystallography, microstructure, and morphology of the hundred-nanometer- to micrometer-thick ZnO films was significant. In this study, we present an unprecedented methodology by combining isotopic tracers with mass spectrometry to elucidate the role of the two different sources of oxygen atoms during the evolution of the growth. Notably, the use of in situ quartz crystal microbalance (QCM) and Secondary Ion Mass Spectrometry (SIMS) reveals new insights into the reaction mechanism for ZnO thin film growth. On the one hand, the non-negative mass change during the ZnO growth without O-2 gas is attributed to the presence of bare zinc atoms on the surface due to the reaction between monoethyl zinc and hydroxyl groups of the water precursor after the diethyl zinc pulse. On the other hand, the detection of ZnxOyC2H5- ions by Time-of-Flight SIMS (TOF-SIMS) and the mass increase during the O-2 pulse suggest a new reaction mechanism for the ZnO thin film growth in the presence of gaseous O-2 where the ethyl ligand of the zinc precursor can react with O-2 to form ethylperoxy radicals. The formations of the ethylperoxy zinc and/or zinc atoms lead to more adsorption of water to form ethylhydroperoxide during the water pulse, inducing the positive mass change. The use of an isotopic substitution allowed us to unambiguously associate the mass gain with the gradual incorporation of gaseous oxygen throughout the growth process and thereby support the chemical reaction. [less ▲]

Critical field anisotropy in the antiferroelectric switching of PbZrO3 films

in APPLIED PHYSICS LETTERS (2021), 118(4),

Antiferroelectrics have been recently sparking interest due to their potential use in energy storage and electrocaloric cooling. Their main distinctive feature is antiferroelectric switching, i.e., the ... [more ▼]

Antiferroelectrics have been recently sparking interest due to their potential use in energy storage and electrocaloric cooling. Their main distinctive feature is antiferroelectric switching, i.e., the possibility to induce a phase transition to a polar phase by an electric field. Here, we investigate the switching behavior of the model antiferroelectric perovskite PbZrO3 using thin films processed by chemical solution deposition in different geometries and orientations. Both out-of-plane and in-plane switching configurations are investigated. The critical field is observed to be highly dependent on the direction of the electric field with respect to the film texture. We show that this behavior is qualitatively consistent with a phase transition to a rhombohedral polar phase. We finally estimate the importance of crystallite orientation and film texturation in the variations observed in the literature. [less ▲]

Single crystal growth of BaZrO3 from the melt at 2700 degrees C using optical floating zone technique and growth prospects from BaB2O4 flux at 1350 degrees C

in CRYSTENGCOMM (2019), 21(3), 502-512

We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single ... [more ▼]

We report the growth of BaZrO3 single crystals by the optical floating zone technique and the investigation on its flux growth using BaB2O4 as a solvent. 6 mm long colorless and transparent single crystals were obtained with a mirror furnace without the need for post-treatment annealing. Its properties are determined and compared with those of two commercial crystals grown by the tri-arc Czochralski method. The chemical composition was investigated using glow discharge mass spectrometry (GDMS) and secondary ion mass spectrometry (SIMS), which indicate minor impurities of Sr, Hf, Ca and Ti, with maximal concentrations for Sr and Hf in the range of 0.3-0.5 at. The optical band gap determined by UV-visible spectroscopy is found to be similar to 4.8 eV and indicates the high quality of the BaZrO3 crystals grown by the optical floating zone technique. Raman spectroscopy at ambient conditions and at low temperatures down to 4.2 K reveals a relatively sharp second-order spectrum and does not reveal any structural phase transition. Prospective high-temperature solution growth using BaB2O4 self-flux was investigated and led to 150-200 mu m BaZrO3 crystals. This solvent opens the way to grow BaZrO3 at half its melting point by the flux method. [less ▲]

Sodium enhances indium-gallium interdiffusion in copper indium gallium diselenide photovoltaic absorbers

in Nature Communications (2018)

Post-deposition treatment of Cu2ZnSnSe4 with alkalis

in Thin Solid Films (2016), 633

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor ... [more ▼]

Low temperature post-deposition treatment of Cu2ZnSnSe4 with NaF and KF significantly improved the solar cell efficiency (from 6.4% to 7.8% and 7.7% on average, respectively) due to enhanced fill factor (from 0.58 to 0.61 and 0.62), open-circuit voltage (Voc) (from 314 mV to 337 mV and 325 mV) and short-circuit current density (from 35.3 mA⋅cm −2 to 38.3 mA⋅cm −2 and 38.6 mA⋅cm −2). Voc improvement was higher for solar cells with NaF treatment due to an increase in radiative efficiency at room temperature and shallower defect activation energy as determined by photoluminescence (PL) and temperature dependent admittance spectroscopy, respectively. In the case of KF treatment, red-shift of the PL, higher band tail density of state and donor activation energy deeper in the band gap were limiting further improvement of the Voc compared to NaF treatment. [less ▲]

13.3% efficient solution deposited Cu(In,Ga)Se 2 solar cells processed with different sodium salt sources

in Progress in Photovoltaics (2015)

Alternative etchning for improved Cu-rich CuInSe2 solar Cells

in Materials Research Society Symposia Proceedings (2015), 1771

Cu2ZnSnSe4 thin film solar cells produced via coevaporation and annealing including a SnSe2 capping layer

in Progress in Photovoltaics (2013), 22(1), 51-57

Cu2ZnSnSe4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe2 capping layer has been ... [more ▼]

Cu2ZnSnSe4 (CZTSe) thin film solar cells have been produced via co-evaporation followed by a high-temperature annealing. In order to reduce the decomposition of the CZTSe, a SnSe2 capping layer has been evaporated onto the absorber prior to the high-temperature treatment. This eliminates the Sn losses due to SnSe evaporation. A solar cell efficiency of 5.1 could be achieved with this method. Moreover, the device does not suffer from high series resistance, and the dominant recombination pathway is situated in the absorber bulk. Finally different illumination conditions (white light, red light, and yellow light) reveal a strong loss in fill factor if no carriers are generated in the CdS buffer layer. This effect, known as red-kink effect, has also been observed in the closely related Cu(In,Ga)Se-2 thin film solar cells. Copyright (c) 2013 John Wiley Sons, Ltd. [less ▲]

HCl and Br2-MeOH etching of Cu2ZnSnSe4 polycrystalline absorbers

in Thin Solid Films (2013), 535