Solar cells having ultrathin active layers
AssigneeMassachusetts Institute of Technology
InventorsJohn C. C. Fan, Carl O. Bozler
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Abstract
Improvements in solar cells based upon low cost semiconductors, such as amorphous silicon, are disclosed. The improved solar cells of this invention have ultrathin active semiconductor layers having a thickness between 0.1 t.sub..alpha. and L.sub.m wherein t.sub..alpha. is the solar spectrum absorption length and L.sub.m is the diffusion length for photogenerated minority charge carriers in the active layer. The back surface reflector has a solar spectrum reflectivity of 70% or greater, so that incident energy not absorbed in a direct pass through the active layer is reflected for another pass. The most preferred embodiment of the cells described herein are shaped to have a light-trapping structure so that light makes multiple passes through the thin semiconductor layers.
Claims16
In a solar cell having an active semiconductor layer consisting essentially of silicon produced from an alloy of amorphous silicon and hydrogen in a glow discharge in silane, said layer having a minority carrier diffusion length, L.sub.m, which is less than the solar spectrum absorption thickness t.sub..alpha. ;
- the improvement of limiting said active layer to a thickness of less than 0.25 .mu.m and providing said active layer with a back surface reflector having a solar spectrum reflectivity of at least about 70%.
A solar cell comprising:
- a. an active layer of a semiconductor consisting essentially of silicon produced from an alloy of amorphous silicon and hydrogen in a glow discharge in silane, said layer having a thickness of less than 0.25 .mu.m;
- b. a junction for maintaining separation of photogenerated charge carriers;
- c. a back surface reflector for said active semiconductor layer, said back surface reflector having a solar spectrum reflectivity of at least about 70%;
- and,
- d. a substrate.
A solar cell comprising an active layer of silicon having a thickness of from about 0.1 .mu.m to about 0.25 .mu.m, a back surface reflector for said layer of silicon, a junction for maintaining separation of photogenerated charge carriers, and a substrate.
Dependencies are inferred from the claim text.