Niobium‐doped TiO₂ films as window layer for chalcopyrite solar cells

Abstract

Smooth and semitransparent Nbx Ti1–x Oy (x = 0.03, y = 1.84–1.91) films have been prepared by reactive magnetron sputtering at temperatures below 420 K. Structural investigations by RAMAN‐spectroscopy together with resistivity‐ and temperature‐dependent Hall‐measurements were used in order to analyze the film structure and the nature of the charge transport in this material. These films can be used as a window layer (TCO) for thin film solar cells. Cu(In,Ga)Se2 solar cells equipped with the new window layer keep their functionality which excludes first, the presence of strong energetic barriers and second, a strong interfacial recombination. The development of TiO2‐based window layers is expected to make thin film solar cells less sensitive against corrosion after contact with humidity. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Combinatorial atmospheric pressure chemical vapour deposition (cAPCVD) of niobium doped anatase; effect of niobium on the conductivity and photocatalytic activity

“…16,19 For niobium doped titanium dioxide films grown on insulting barrier glass substrates (SiO 2 ), much lower resistivities were observed ranging from 1.3 Â 10 À3 Um to 9 Â 10 À3 Um. 17,18 Post treatment annealing of these films in air lead to a further reductions in conductivity by a factor of z 2; verifying predictions made by the DFT calculations that suggested oxygen vacancies were of vital importance for enhanced conductivity properties. 21 Nb doped anatase systems also show potential for sensitive oxygen gas sensors, with better response times compared with un-doped anatase.…”

“…The most conductive positions were observed in areas where film growth was rapid, with resistivity minimising at positions F1 (13.9 nm s À1 growth) in NbTiO 2 -A and F13 (12.5 nm s À1 growth) in NbTiO 2 -B. Although the resistivities observed in this study were larger than those observed in the literature, [13][14][15][16][17][18][19][20][21] previous films were typically deposited onto conductive substrates as opposed to insulting barrier glass used in this work.…”

“…[5][6][7][8][9][10][11][12] There has been considerable interest of late into transition metal doping of anatase to enhance the conductivity properties for optoelectronic applications. [13][14][15][16][17][18][19][20][21][22][23] The benefits of doping anatase thin-films for use as transparent conducting oxides (TCO) or TCO protective layers are clear given their durability to humidity or acid degradation compared with traditional tin and zinc oxide based TCOs. One such method has included doping of anatase with niobium with resistivities as low as r ¼ 2.3 Â 10 À6 Um for films grown on SrTiO 3 substrates; 13 comparable to that of indium tin oxide (ITO).…”

“…26,27 Niobium doped anatase systems reported in the literature were uniform films formed primarily via either DC magnetron sputtering or pulsed laser deposition. [13][14][15][16][17][18][19][20][21][22][23] The high (40 at %) solubility limit of niobium substitution within anatase was attributed to the similar ionic radii of Nb 5+ (0.78 A) and Ti 4+ (0.75 A). 14 Although individual thin-films of niobium (V) oxide and anatase titanium dioxide have been grown by chemical vapour deposition (CVD), 28,29 a niobium doped anatase system has yet to be synthesised by this technique.…”

TiO2-based transparent conducting oxides; the search for optimum electrical conductivity using a combinatorial approach

“…6 TiO 2 is inexpensive, non-toxic, chemically stable over a wide range of pH and electrically stable over a wide range of voltage. The benets of improving TiO 2 thin-lms for TCO applications are clear given the material's enhanced impermeability, acid stability, 28 hydrogen radical exposure stability 29,30 and long wavelength transparency when compared with traditional materials such as In 2 O 3 , SnO 2 , CdO and ZnO. [7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26] For several years the bulk of transparent conducting oxide (TCO) research has focused on improving SnO 2 , 27 with signicant improvement now unlikely.…”