THIN-FILM SOLAR CELL HAVING A MOLYBDENUM-CONTAINING BACK ELECTRODE LAYER
A thin-film solar cell has a rear electrode layer formed of at least 50 atom % of Mo, which in addition to the common contaminants includes 0.1 to 45 atom % of at least one element from the group of Ti, Zr, Hf, V, Nb, Ta, and W, 0 to 7.5 atom % of Na, and 0 to 7.5 atom % of at least one element forming a compound with Na that has a melting point >500 C. The rear electrode layer has good long-term resistance and bonding with the CIGS absorber layer. In addition, the constancy of the alkali metal integration in the absorber layer is improved.
1 - 23 . (canceled)
24 . A thin-film solar cell, comprising:
at least one substrate, a back electrode layer, an absorber layer, and a front contact layer;
said back electrode layer being formed of one or more coating layers and at least one coating layer of said back electrode layer consisting of:
from 0.1 to 45 atom % of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, and W;
from 0 to 7.5 atom % of Na;
from 0 to 7.5 atom % of one or more elements forming a compound with Na having a melting point above 500° C.; and
balance of at least 50 atom % of Mo and impurities.
25 . The thin-film solar cell according to claim 24 , wherein at least one said coating layer of said back electrode layer contains from 0.01 to 7.5 atom % of Na.
26 . The thin-film solar cell according to claim 24 , wherein a content of Ti is from 1 to 30 atom %, a content of Zr is from 0.5 to 10 atom %, a content of Hf is from 0.5 to 10 atom %, a content of V is from 1 to 20 atom %, a content of Nb is from 1 to 20 atom %, a content of Ta is from 1 to 15 atom %, and a content of W is from 1 to 40 atom %.
27 . The thin-film solar cell according to claim 26 , wherein the content of Ti is from 2 to 20 atom %, the content of Zr is from 1 to 5 atom %, the content of Hf is from 1 to 5 atom %, the content of V is from 2 to 10 atom %, the content of Nb is from 2 to 10 atom %, the content of Ta is from 2 to 10 atom %, and the content of W is from 5 to 35 atom %.
28 . The thin-film solar cell according to claim 24 , wherein said back electrode layer contains from 0.01 to 7.5 atom % of at least one element selected from the group consisting of 0, Se, and S.
29 . The thin-film solar cell according to claim 24 , wherein said back electrode layer has a thickness of from 0.05 to 2 μm.
30 . The thin-film solar cell according to claim 24 , wherein at least one said coating layer of said back electrode layer contains Na and Ti.
31 . The thin-film solar cell according to claim 24 , wherein at least one said coating layer of said back electrode layer contains Na and W.
32 . The thin-film solar cell according to claim 24 , wherein said back electrode layer is formed of a single coating layer.
33 . The thin-film solar cell according to claim 32 , wherein said back electrode layer contains from 0.5 to 2.5 atom % of Na.
34 . The thin-film solar cell according to claim 24 , wherein said back electrode layer is formed of two coating layers.
35 . The thin-film solar cell according to claim 34 , wherein at least one of said two coating layers contains from 1.5 to 7.5 atom % of Na.
36 . The thin-film solar cell according to claim 24 , wherein said absorber layer is a chalcopyrite absorber layer.
37 . A sputtering process, which comprises:
providing a sputtering target consisting of:
production dependent impurities;
from 0.1 to 45 atom % of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, and W;
from 0 to 7.5 atom % of Na;
from 0 to 7.5 atom % of one or more elements that form a compound having a melting point of greater than 500° C. with Na; and
a balance of at least 50 atom % of Mo; and
sputtering from the sputtering target for producing a back electrode layer of the thin-film solar cell according to claim 24 .
38 . A sputtering target for producing a back electrode layer of a thin-film solar cell having a molybdenum content of at least 50 atom %, the sputtering target comprising:
from 0.1 to 45 atom % of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, and W;
from 0.01 to 7.5 atom % of Na;
from 0.005 to 15 atom % of one or more elements that form a compound with Na having a melting point of greater than 500° C.; and
balance usual impurities.
39 . The sputtering target according to claim 38 , wherein:
a content of Ti is from 1 to 30 atom %;
a content of Zr is from 0.5 to 10 atom %;
a content of Hf is from 0.5 to 10 atom %;
a content of V is from 1 to 20 atom %;
a content of Nb is from 1 to 20 atom %;
a content of Ta is from 1 to 15 atom %; and
a content of W is from 1 to 40 atom %.
40 . The sputtering target according to claim 39 , wherein:
the content of Ti is from 2 to 20 atom %;
the content of Zr is from 1 to 5 atom %;
the content of Hf is from 1 to 5 atom %;
the content of V is from 2 to 10 atom %;
the content of Nb is from 2 to 10 atom %;
the content of Ta is from 2 to 10 atom %; and
the content of W is from 5 to 35 atom %.
41 . The sputtering target according to claim 38 , wherein a Na content is from 0.1 to 5 atom %.
42 . The sputtering target according to claim 41 , wherein the Na content is from 0.5 to 2.5 atom %.
43 . The sputtering target according to claim 38 , wherein the sodium compound is at least one compound from the group consisting of sodium oxide, sodium mixed oxide, sodium selenide, sodium sulfide, and sodium halides.
44 . The sputtering target according to claim 38 , wherein at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, and W is present in elemental form, as a solution in Mo, in the form of a mixed crystal, or as constituent of the sodium-containing compound.
45 . The sputtering target according to claim 38 , wherein the sodium-containing compound is a two-component or multi-component sodium mixed oxide, where one component is Na 2 O and a further component is an oxide of at least one element selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, W, Si, and Ge.
46 . The sputtering target according to claim 45 , wherein the sodium-containing compound is at least one compound selected from the group consisting of sodium tungstate, sodium titanate, sodium niobate, and sodium molybdate.
47 . The sputtering target according to claim 38 , comprising a matrix phase composed of Mo or a Mo mixed crystal formed from one or more elements selected from the group consisting of Ti, Zr, Hf, V, Nb, Ta, and W, wherein a particle size of the matrix phase is from 0.1 to 50 μm and Na or the Na-containing compound is present in interstices of the matrix phase.