Work Function Modification of Tungsten-Doped Indium Oxides Deposited by the Co-Sputtering Method

Abstract

We have studied the work function modification of tungsten-doped indium oxides (IWOs) through the co-sputtering of indium oxide (In2O3) and indium tungsten oxide (In2O3 80 wt% + WO3 20 wt%) via a radio frequency (RF) magnetron sputtering system. By controlling the elemental deposition of IWOs, the resultant work functions varied from 4.37 eV to 4.1 eV. The IWO thin films showed excellent properties for application as transparent conducting oxide materials in the region of 0 to 2.43 at.% of tungsten versus the total metal content. The carrier concentration of n-type IWO thin films varied from 8.39 x 10(19) cm(-3) to 8.58 x 10(21) cm(-3), while the resistivity varied from 3.15 x 10(-4) Ωcm to 2.26 x 10(-3) Ωcm. The largest measured optical band gap was 3.82 eV determined at 2.43 at.% of tungsten atoms relative to the total amount of metal atoms, while the smallest optical band gap was 3.6 eV at 4.78 at.% of tungsten. IWO films containing more than 2.43 at.% of tungsten atoms relative to the total number of metal atoms revealed an average transmittance of over 80% within the visible light region.

Sputtered Tungsten Oxide as Hole Contact for Silicon Heterojunction Solar Cells

“…A reduced band bending at the WO x /silicon-interface was identified as the reason of this low fill factors [14]. So far most studies used thermal evaporation for the preparation of metal oxide contact layers and sputtering has only been applied to molybdenum oxide layers [17], or in other fields of materials research [18], [19]. Unfortunately thermal evaporation does not allow for intentional modification of the oxygen vacancy density in metal oxide layers.…”

Electronic structure of indium-tungsten-oxide alloys and their energy band alignment at the heterojunction to crystalline silicon

“…The consequential idea is to combine both materials and search for a trade-off. There are reports on indium-tungsten-oxide (IWO x ) layers with up to 7 % WO x applied as transparent conductive oxides 11,28 . These layers are among the doped indium oxide layers with the highest mobility 11 .…”

Evolution of Optical, Electrical, and Structural Properties of Indium Tungsten Oxide upon High Temperature Annealing

“…The tungsten oxide fraction in these mixtures either stays amorphous, or the W 6þ ions partially substitute [34] the In 3þ ions in the crystal structure, due to their similar ionic radii of 0.74 and 0.94 Å, respectively. [23] In Figure 4, a tentative crystallization diagram, based on these observations, is shown. Note that the layers were annealed at T Anneal first and then measured at room temperature.…”

“…Here, the aim is to alloy both metal oxides to form either a more conductive amorphous mixture or a mix of segregated phases that possesses a higher conductivity than the pure tungsten oxide. Note that there have also been studies of tungsten-doped indium oxide [21][22][23] (In 2 O 3 :W) as transparent conductive oxide (TCO)-thus, In 2 O 3 with the addition of a few percent of tungsten, but with a different purpose: The indium oxide was doped to increase the conductivity. The work function is not significantly increased for small amounts of tungsten doping.…”

“…The work function is not significantly increased for small amounts of tungsten doping. [23] Here, we aim at keeping the high work function of the tungsten oxide, to obtain a material, that is suitable as recombination contact for common solar cell absorbers, such as silicon. In previous studies, we already showed how the indium tungsten oxide (IWO x ) work function and band bending at the interface toward crystalline silicon can be manipulated by DOI: 10.1002/pssa.202000165 Optical, structural and electrical properties of thermally co-evaporated indium tungsten oxide (IWO x ) thin films with varied stoichiometry, from pure tungsten oxide to pure indium oxide (InO x ) are investigated upon stepwise annealing, up to 700 C. The thin films are candidate materials for carrier selective contacts in different types of solar cells, such as silicon hetero junction and perovskite solar cells.…”