US Patent 7442320 - Si + Ge quantum dot composites for photovoltaics

http://www.freepatentsonline.com/7442320.html

This patent from Ultradots, inc. takes advantage of band offsets between silicon and germanium semiconductor nanocrystals in the formation of high efficiency photovoltaics. Claim 1 reads:

1. A nanostructured material, comprising:

(a) a first nano-network formed from a plurality of Si quantum dots that are at least one of fused and interconnected; and

(b) a second nano-network coupled to said first nano-network and formed from a plurality of Ge quantum dots that are at least one of fused and interconnected,

said plurality of Si quantum dots having a first peak size that is from about 1 nm to about 20 nm, said plurality of Ge quantum dots having a second peak size that is greater than said first peak size to define a staggered band offset between said first nano-network and said second nano-network,

said nanostructured material being configured to absorb light to produce a first type of charge carrier and a second type of charge carrier, said first type of charge carrier separating into said first nano-network in accordance with said staggered band offset and being-transported in said first nano-network, said second type of charge carrier separating into said second nano-network in accordance with said staggered band offset and being transported in said second nano-network, said nanostructured material having an absorption coefficient that is at least 1000/cm within a range of wavelengths from about 400 nm to about 700 nm.