Optical characterization of low temperature amorphous MoOx, WOX, and VOx prepared by pulsed laser deposition

Sub-gap defect density characterization of molybdenum oxide: An annealing study for solar cell applications

“…The optical absorption of the samples was extracted from a photothermal deflection spectroscopy (PDS) setup [44,45], by measuring the deflection of a He-Ne laser beam tangent to the sample edge. This deflection is proportional to the absorption within the sample and exhibits superior sensitivity over transmittance/reflectance spectrophotometry; as such, it has been extensively used to analyze electronic defects in semiconductors [48] and recently, to characterize amorphous transition metal oxides as MoOx, WOx and VOx [49]. Finally, measurements of conductivity have been performed in a co-planar configuration after the deposition of two aluminum electrodes on the MoOx films.…”

Impact of a Spun-Cast MoOx Layer on the Enhanced Moisture Stability and Performance-Limiting Behaviors of Perovskite Solar Cells

“…34,35 The optical band gap of amorphous MoO x was found to lie in a range of 3.0−3.5 eV and greatly depended on the preparation conditions. 36,37 Cauduro et al reported a band gap of 3.06 eV for substoichiometric MoO 2.57 films. On the other hand, the optical band gap is 3.29 eV when a stoichiometric MoO 3 layer is deposited.…”

“…Nevertheless, coating a perovskite layer with a higher MoO x concentration is expected to lower the absorption of the sample due to the possibility of light scattering in the MoO x layer, where optical reflection losses occur. It has been reported that the reflective index of the MoO x film was in the range of 2.00–2.25 at a solar radiation wavelength of 750 nm depending on the preparation conditions. , However, reflective indices of 2.5 for MAPbI 3 and 2.1 for MAPbBr 3 were reported. , It is worth mentioning that the minimal reflection loss is obtained when the optical index of the coating layer is equal to the square root of the surrounding medium’s reflective index multiplied by the index of reflection of the substrate being used. , The optical band gap of amorphous MoO x was found to lie in a range of 3.0–3.5 eV and greatly depended on the preparation conditions. , Cauduro et al reported a band gap of 3.06 eV for substoichiometric MoO 2.57 films. On the other hand, the optical band gap is 3.29 eV when a stoichiometric MoO 3 layer is deposited…”

Unveiling the Effect of Potassium Treatment on the Mesoporous TiO2/ Perovskite Interface in Perovskite Solar Cells

“…The K treatment considerably decreases the sub-band-gap absorption and exhibits an outstanding improvement in the density of states toward the band edge of TiO 2 , as shown in Figure a, which can facilitate the carrier mobility in TiO 2 and thereby significantly enhance the charge transport across the mesoporous TiO 2 film in a PSC . In the PDS spectra, the Urbach energy E u was calculated from the slope of the absorptance at the band edge. , The fitting of PDS absorptance spectra to evaluate the Urbach energies is provided in Figure S8. As shown in the inset of Figure a, the estimated E u of both pristine and K-treated mesoporous TiO 2 are 111.1 and 95.9 meV, respectively, indicating that the K treatment results in a considerable reduction in the density of electron trap states.…”

“…45 In the PDS spectra, the Urbach energy E u was calculated from the slope of the absorptance at the band edge. 46,47 The fitting of PDS absorptance spectra to evaluate the Urbach energies is provided in Figure S8. As shown in the inset of Figure 2a, the estimated E u of both pristine and K-treated mesoporous TiO 2 are 111.1 and 95.9 meV, respectively, indicating that the K treatment results in a considerable reduction in the density of electron trap states.…”