HB's idea sounds very promising, if you can develop theory and experiment and nanofab technologies to help with it... The 4-gap idea used in the record setting cell is a huge pain. If somehow we could manufacture (and do it well) quantum dots with controllable properties that varied spatially as desired, then we could presumably have energy gaps forming a continuum, allowing perfectly tailored access to entire solar spectrum, and without weird rare chemicals. That'd be the dream. Whether it merely is a pipe dream, that is the question. As far as I know some green plants and algae do have several kinds of chlorophyll-containing macro-molecular assembly, each tailored to different region of spectrum, but no single life form employs a continuum. (If this was such a great idea, then why not?) Perhaps however a community of 1000 algal species layered at different depths in water could be argued to form such a continuum (not a realistic model of nature). And also, far as I know, the overall efficiency of green plants at converting to sunlight to biomass=fuel is way worse than that 35% efficient solar cell. What if the plants were living in a massively-CO2-rich atmosphere? Would they be efficient then? -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)