Front electrode with thin metal film layer and high work-function buffer layer for use in photovoltaic device and method of making same
This invention relates to a front electrode or contact for use in an electronic device such as a photovoltaic device. In certain example embodiments, the front electrode of the photovoltaic device includes a highly conductive metal film and a thin high work-function buffer layer. The high-work function buffer layer is located between the metal film and the uppermost semiconductor layer so as to provide for substantial work-function matching between the metal film and the high work-function uppermost semiconductor layer so as to reduce a potential barrier for holes extracted from the device by the front electrode/contact. Optionally, a layer such as a transparent conductive oxide (TCO) or a dielectric may be provided between a front glass substrate and the metal film.
1 . A photovoltaic device comprising:
a front glass substrate;
an active semiconductor film;
an electrically conductive and substantially transparent front electrode structure located between at least the front glass substrate and the semiconductor film;
wherein the front electrode structure comprises a substantially transparent metal film, and a high work function buffer film; and
wherein the high work function buffer film has a work-function that is higher than a work-function of the metal film, and the high work function buffer film is located between the metal film and an uppermost portion of the semiconductor film.
2 . The photovoltaic device of claim 1 , wherein the high work function buffer film comprises a TCO film.
3 . The photovoltaic device of claim 1 , wherein the high work function buffer film comprises indium tin oxide.
4 . The photovoltaic device of claim 1 , wherein the high work function film comprises oxygen-rich indium-tin-oxide (ITO).
5 . The photovoltaic device of claim 1 , wherein the metal film comprises first and second substantially metallic layers made of different metals.
6 . The photovoltaic device of claim 1 , wherein the high work function buffer film directly contacts each of the metal film and the semiconductor film.
7 . The photovoltaic device of claim 1 , wherein the metal film has a work-function of no greater than about 4.2 eV, and the high work function buffer film has a work function of at least 4.3 eV.
8 . The photovoltaic device of claim 1 , wherein the high work function buffer film has a work function of at least about 4% higher than that of the metal film, more preferably at least 6% higher, and most preferably at least about 10% higher.
9 . The photovoltaic device of claim 1 , wherein the high work function buffer film has a work-function of from about 4.0 to 5.7 eV.
10 . The photovoltaic device of claim 1 , wherein the high work function buffer film has a work-function of from about 4.3 to 5.2 eV.
11 . The photovoltaic device of claim 1 , wherein the high work function buffer film has a work-function of from about 4.5 to 5.0 eV.
12 . The photovoltaic device of claim 1 , wherein the metal film comprises one or more of Cu, Ag, Au, Al, Ni and/or Pd.
13 . The photovoltaic device of claim 1 , wherein the metal film comprises a first layer consisting essentially of a first metal(s), and a second layer consisting essentially of a different second metal(s).
14 . The photovoltaic device of claim 1 , wherein the metal film is from about 20-600 angstroms thick, and the high work function buffer film is from about 10 to 1,000 angstroms thick.
15 . The photovoltaic device of claim 1 , wherein the metal film is from about 40-200 angstroms thick, and the high work function buffer film is from about 10 to 100 angstroms thick.
16 . The photovoltaic device of claim 1 , further comprising a nucleation film located between the front glass substrate and the metal film.
17 . The photovoltaic device of claim 16 , wherein the nucleation film comprises a transparent conductive oxide.
18 . The photovoltaic device of claim 1 , wherein the high work function buffer film is a dielectric film.
19 . The photovoltaic device of claim 1 , wherein the high work function buffer film is a dielectric and has a thickness of from about 5-30 angstroms.
20 . The photovoltaic device of claim 1 , wherein the semiconductor film comprises hydrogenated amorphous silicon.
21 . The photovoltaic device of claim 1 , further comprising a back electrode, wherein the active semiconductor film is provided between at least the front electrode and the back electrode.
22 . The photovoltaic device of claim 1 , wherein the high work function barrier film is oxidation graded, continuously or discontinuously, so as to have a higher oxygen content adjacent the semiconductor film than adjacent the metal film.
23 . An electrode structure adapted for use in a photovoltaic device, the electrode structure comprising:
a glass substrate;
a substantially transparent metal film supported by the glass substrate;
a high work function buffer film supported by the glass substrate, wherein the high work function buffer film has a work-function that is higher than a work-function of the metal film, and the metal film is located between at least the high work function buffer film and the glass substrate.
24 . The electrode structure of claim 23 , wherein the high work function buffer film comprises a TCO film.
25 . The electrode structure of claim 23 , wherein the metal film comprises first and second different substantially metallic layers.
26 . The electrode structure of claim 23 , wherein the high work function buffer film directly contacts the metal film and is also adapted to directly contact a semiconductor film of the photovoltaic device.
27 . The electrode structure of claim 23 , wherein the metal film has a work-function of no greater than about 4.2 eV, and the high work function buffer film has a work function of at least 4.3 eV, and wherein the high work function buffer film has a work function of at least about 4% higher than that of the metal film.
28 . The electrode structure of claim 23 , wherein the metal film is from about 40-200 angstroms thick, and the high work function buffer film is from about 10 to 100 angstroms thick.
29 . The electrode structure of claim 23 , further comprising a nucleation film located between the glass substrate and the metal film, wherein the nucleation film comprises a metal oxide.
30 . The electrode structure of claim 23 , wherein the high work function buffer film is a dielectric film and has a thickness of from about 5-30 angstroms.