Extrinsic Defects in Crystalline MoO₃: Solubility and Effect on the Electronic Structure

Abstract

The effect of six potential contaminants (Cu, In, Ga, Se, Sn, and Zn) and five potential dopants (Ti, Mn, Sc, V, and Y) on the electronic and optical properties of molybdenum oxide (MoO 3 ) contact layers for solar cells was investigated using point defect analysis based on density functional theory simulations. Of the contaminants investigated, Sn, In, and Ga were found to be highly insoluble at all relevant temperatures and pressures and therefore not a concern for solar cell manufacturing. Zn, Cu, and Se exhibit some solubility, with the latter two appearing to introduce detrimental defect states near the valence band. This contamination can be avoided by increasing the O 2 partial pressure during MoO 3 deposition. Of the five potential aliovalent dopants, Sc, Ti, and Y were disregarded because of their limited solubility in MoO 3 , whereas V was found to be highly soluble and Mn somewhat soluble. The effect of Mn and V doping was shown to be strongly dependent on the O 2 partial pressure during deposition, with a high pO 2 favoring the formation of substitutional defects (potentially beneficial in the case of Mn doping because of the addition of defect states near the conduction band), whereas low pO 2 favoring interstitial defects.

Robust Inorganic Hole Transport Materials for Organic and Perovskite Solar Cells: Insights into Materials Electronic Properties and Device Performance

“…The most widely used manufacturing method for NiO involves the thermal sol–gel decomposition of nickel hydroxide, with thermal evaporation being the most commonly used deposition method. [ 81,95,96 ] Other successful deposition methods include pulsed laser deposition and solution‐processed NiO. [ 97,98 ]…”

“…The most widely used manufacturing method for NiO involves the thermal sol-gel decomposition of nickel hydroxide, with thermal evaporation being the most commonly used deposition method. [81,95,96] Other successful deposition methods include pulsed laser deposition and solutionprocessed NiO. [97,98] The thermodynamically most abundant defect is the nickel vacancy (V Ni ), [99,100] whose twofold negative charge is compensated by the stabilization within the lattice of Ni 3þ cations, resulting in p-type self-doping.…”

“…Density functional theory (DFT) calculations have predicted that three sites are stable for substitutional doping, as shown in Figure 4g, with i1 and i3 interstitial sites being the most preferable for different ions including sodium (Na), potassium (K) (also preferring i2, i3 sites), [ 80 ] indium (In), manganese (Mn), and gallium (Ga) (also preferring i2 sites). [ 81 ] A bandgap reduction is observed in all cases due to the creation of intergap states (Figure 4h), which are generally closer to the CBM, except for doping with copper (Cu), which serves as a p‐type interstitial dopant, hence inducing gap states near the VBM.…”

Structural Evolution of MoO3 Thin Films Deposited on Copper Substrates upon Annealing: An X-ray Absorption Spectroscopy Study

“…The dipole nature of the α-MoO 3 layers is at the origin of its relatively high work function (WF) of about 6.5 eV [1,5]. Moreover, despite its insulator nature and high WF, previous studies pointed out that thin MoO 3 films may exhibit a conductive behavior in the presence of defects and oxygen vacancies [6][7][8][9][10] or via interaction with a metallic substrate such as copper [7].…”