Resilience of Cuprous Oxide under Oxidizing Thermal Treatments via Magnesium Doping

Abstract

This study reports the influence of the magnesium incorporation into cuprous oxide (Cu2O) on its transformation in cupric oxide (CuO). Thermal treatments under oxidizing conditions are performed on undoped and magnesium-doped cuprous oxide thin films, Cu2O and Cu2O:Mg respectively, deposited by aerosol-assisted metal organic chemical vapour deposition. The oxidation kinetics of these films shows a slower rate in the Cu2O:Mg system, since the complete oxidation into CuO occurs at a higher temperature when compared to undoped Cu2O. The increased stability of Cu2O:Mg can be explained by the inhibition of the formation of split copper vacancies, the defect most frequently associated with the CuO nucleation. Annealing treatments performed on Cu2O thin films provide new insights on the dopant influence on the mechanism to generate simple and split copper vacancies as well as the transformation of Cu2O into CuO.drastically the resistivity of Cu2O to 10 -2 Ω.cm, 22 which consequently allowed an increase of 8.1% maximum efficiency in this Cu2O-based solar cells, in a MgF2/ZnO:Al/Zn0.38Ge0.62O/Cu2O:Na heterojunction. 23 This record of efficiency was achieved by thermal oxidized Cu2O, which is unsuitable for industrialization of low cost solar cells, since Supprimé: , grown in these cases Mis en forme : Indice

Grain-boundary segregation of magnesium in doped cuprous oxide and impact on electrical transport properties

“…For intrinsic Cu 2 O samples we obtained a reduction of the resistivity only during the 250 °C annealing step, leading to a final room temperature value for the resistivity of 80 ± 1 Ω cm, presented in Table 1 . The annealing treatments at 350 °C and 450 °C increase the resistivity, leading to a final resistance higher than that of the original film, especially in the 450 °C case, where the resistivity reaches 1650 ± 10 Ω cm, allegedly attributed to the formation of CuO, as previously reported 17 . For the Cu 2 O:Mg thin films, we observed a different trend when compared to the intrinsic Cu 2 O samples, since all the thermal treatments lead to a reduction of the final resistivity at room temperature compared to the initial value, with the lowest resistivity value of 13.3 ± 0.1 Ω cm observed for the sample annealed at 450 °C, presented on Table 1 .…”

“…It is expected that this complex prevents the formation of split vacancies for a single cation vacancy, since the divalent cation would assume a position similar to a split copper vacancy ( V split ) in the crystallographic structure 42 . As a consequence, Cu 2 O:Mg materials present an increased response in photoconductivity 14 and exhibit improved chemical stability at high temperatures 14 , 17 , as already reported in the literature. Additionally, this complex would further increase the charge carrier density after annealing treatments in oxidizing conditions, by a simple copper vacancy doping mechanism assisted by the magnesium incorporation 13 .…”

“…Charged molecules, including hydride ions, are commonly detected when field-evaporating covalently or ionically bonded materials 27 , 28 , and hence their presence in the mass spectrum does not reflect the chemistry of the Cu 2 O film. Indeed, previous studies on Cu 2 O:Mg thin films confirm the sole presence of crystalline cuprous oxide, Cu 2 O, by XRD, Raman, TEM and FTIR 14 , 16 , 17 . Considering the complex processes that are intrinsically related to field evaporation and/or the behaviour of molecular ions in high electric fields (e.g.…”

“…In the specific case of magnesium incorporation in Cu 2 O, this dopant showed a strong effect on the resistivity, reaching values as low as 7 Ω cm 16 , by increasing the charge carrier density up to 8.1 × 10 17 cm −3 . Besides, this dopant increases the stability of the Cu 2 O phase under thermal oxidizing treatments 17 . Additionally, several all-oxide solar cells have been produced with Mg-doped Cu 2 O, by using TiO 2 14 and ZnO 15 as n-type counterparts, reporting efficiency values close to 1%.…”

Optimized Stoichiometry for CuCrO2 Thin Films as Hole Transparent Layer in PBDD4T-2F:PC70BM Organic Solar Cells

“…Their intensity increases with Cu content, suggesting a greater number of defects for = 65% when compared to = 40%. For = 67%, spectra (3) in Figure 1 b, the E u mode of the CuCrO 2 at 96 cm −1 is detected, while additional Raman modes, at 108 cm −1 , 149 cm −1 , 216 cm −1 , 495 cm −1 , and 649 cm −1 are attributed to the presence of the Cu 2 O phase [ 48 ]. This statement is confirmed by the comparison with the spectrum of pure Cu 2 O deposited in the same deposition conditions ( Figure 1 b, spectra (4)).…”