Solar cell texturing
Multicrystalline silicon (mc-Si) solar cells having patterned light trapping structures (e.g., pyramid or trough features) are generated by printing a liquid mask material from an array of closely-spaced parallel elongated conduits such that portions of the mc-Si wafer are exposed through openings defined between the printed mask features. Closely spaced mask pattern features are achieved using an array of conduits (e.g., micro-springs or straight polyimide cantilevers), where each conduit includes a slit-type, tube-type or ridge/valley-type liquid guiding channel that extends between a fixed base end and a tip end of the conduit such that mask material supplied from a reservoir is precisely ejected from the tip onto the mc-Si wafer. The exposed planar surface portions are then etched to form the desired patterned light trapping structures (e.g., trough structures).
1. A method for generating a patterned light trapping structure on a planar surface of a multi-crystalline silicon wafer, the method comprising:
transmitting a liquid mask material along a plurality of parallel elongated conduits such that a portion of said mask material is ejected from a tip portion of each said conduit;
moving the multi-crystalline silicon wafer under the tip portions of the plurality of conduits such that the ejected mask material portions form a mask pattern on the planar surface of the multi-crystalline silicon wafer, wherein said mask material pattern is formed such that a portion of said planar surface is exposed through said mask material pattern; and
etching the exposed planar surface portion such that the etched multi-crystalline silicon wafer forms the integral patterned light trapping structure.
2. The method of claim 1 , wherein each of the plurality of conduits comprises a capillary channel extending between a base portion and the tip portion, said capillary channel having a nominal channel width in the range of 3 to 10 microns, and wherein transmitting the liquid mask material comprises causing a sufficient amount of said liquid mask material to flow along said capillary channels such that said ejected mask material ejected from each said capillary channel forms a mask feature on said surface having a nominal width of 10 microns or less.
3. The method of claim 2 , wherein transmitting the liquid mask material further comprises supplying the liquid mask material to a printhead comprising a substrate having a reservoir, wherein said plurality of conduits are attached to and extend from said substrate, and wherein said liquid mask material is supplied to said reservoir such that said ejected mask material portions simultaneously flow from said reservoir along said plurality of conduits.
4. The method of claim 3 , wherein moving the multicrystalline silicon wafer comprises conveying the multicrystalline silicon wafer at a speed of at least 125 mm/s under the plurality of conduits.
5. The method of claim 4 , wherein each of the plurality of closely-spaced conduits comprises a curved micro-spring structure having said base portion attached to the substrate and said tip portion disposed away from said substrate, and wherein transmitting the liquid mask material comprises causing said ejected mask material portions to simultaneously flow along capillary channels defined by portions of said each micro-spring structure.
6. The method of claim 5 , wherein transmitting the liquid mask material comprises causing each said ejected mask material portion to flow along a corresponding slit-like capillary channel defined between associated pairs of said plurality of micro-springs.
7. The method of claim 5 , wherein transmitting the liquid mask material comprises causing said each said ejected mask material portion to flow through a corresponding tube-like capillary channel defined in an associated one of the plurality of micro-springs.
8. The method of claim 5 , wherein transmitting the liquid mask material comprises causing said each said ejected mask material portion to flow along an associated liquid guiding channel structure disposed on an associated one of the plurality of micro-springs.
9. The method of claim 4 , wherein the plurality of closely-spaced conduits comprises a plurality of straight cantilever sections having a base portion attached to the substrate and said tip portion disposed away from said substrate, and wherein transmitting the liquid mask material comprises causing said ejected mask material portions to simultaneously flow along corresponding slit-like capillary channels defined between adjacent pairs of said plurality of straight cantilever sections.
10. The method of claim 4 , wherein transmitting the liquid mask material comprises delivering said liquid mask material through one or more inkjet printheads to said plurality of conduits.
11. The method of claim 4 , wherein transmitting a liquid mask material comprises delivering said liquid material through one or more pressurized manifolds to said plurality of conduits.
12. The method of claim 4 , wherein transmitting a liquid mask material comprises controlling a viscosity gradient of said liquid mask material delivered to said plurality of conduits by heating said substrate adjacent to said reservoir.
13. The method of claim 1 , wherein transmitting the liquid mask material comprises forcing the liquid mask material along a first set of parallel conduits and a second set of parallel conduits, the first set being offset from the second set in a moving direction of the multicrystalline wafer, wherein the first set of parallel conduits are offset from the second set of parallel conduits in a cross-process such that each first mask feature generated by a conduit of the first set is disposed between a pair of second mask features generated by corresponding conduits of the second set.
14. The method of claim 1 , wherein transmitting the liquid mask material comprises simultaneously delivering the liquid mask material to a plurality of series-arranged conduits such that a first ejected mask material portion ejected from a first conduit is deposited on top of a second ejected mask material portion ejected from a second series-arranged conduit.
15. The method of claim 14 , wherein transmitting the liquid mask material comprises delivering the liquid mask material to multiple sets of series-arranged conduits such that said ejected mask material portion is simultaneously ejected from each of the multiple sets onto a corresponding said multi-crystalline wafer.
16. The method of claim 1 ,
wherein transmitting the liquid mask material comprises continuously delivering the mask material to each of the plurality of conduits such that said ejected mask material portions form continuous elongated parallel mask material lines separated by elongated exposed planar surface portions of the multi-crystalline silicon wafer, and
wherein said etching comprises etching said elongated exposed planar surface portions such that said etching produces elongated groove-type light trapping structures.
17. The method of claim 16 , wherein transmitting a liquid mask material further comprises reciprocating the plurality of parallel elongated conduits in a direction perpendicular to a movement direction of the wafer such that the ejected mask material portions forms parallel wavy mask material lines on the multi-crystalline silicon wafer.
18. The method of claim 1 ,
wherein transmitting the liquid mask material comprises forming ejected mask material portions that define dot-like exposed planar surface portions of said multi-crystalline silicon wafer on the multi-crystalline silicon wafer, and
wherein etching the exposed planar surface portions comprises etching the dot-like exposed regions of said multi-crystalline silicon wafer to form pit-type light trapping structures.
19. The method of claim 1 , wherein transmitting the liquid mask material comprises intermittently contacting the tip portions of the plurality of conduits against the planar surface of the multi-crystalline silicon wafer such that said ejected mask material portions form dot-like mask material structures on the multi-crystalline silicon wafer.
20. The method of claim 1 , wherein transmitting said liquid mask material comprises delivering said liquid mask material to first and second printheads having offset conduits such that first portions of said mask material ejected from tip portions of said conduits disposed on the first printhead are disposed between second portions of said mask material ejected from tip portions of said conduits disposed on the second printhead.