UC Berkeley Announces Organic TE Milestone (or is that Millstone?)

If (1 + 1 = 2) then (grass is green). The premise: true. The conclusion: true. The argument: false. In both their press release [1] and their article in Science [2] a UC Berkeley group suggest their (very nice) measurements of the Seebeck coefficient of individual organic molecules “offers the promise of efficient thermoelectric energy conversion devices” [from 2]. As far as I am aware these are indeed the first Seebeck measurements on individual organic molecules. And very nice measurements they are, resulting in S = +8.7, +12.9 and +14.2 microV/K for three different molecules. And I have to agree that organics are of some interest for thermoelectricity. They are inexpensive, come in infinite variety and often have attractively low thermal conductivity. Organic polymers, for example, can be better conductors than copper [3] and (others) can have Seebeck values over 1000 microV/K [4]. The trick, of course, is bringing these properties together in a single material, something which hasn’t happened yet. I noted all these things years ago [5,6]. If (1 + 1 = 2) then (grass is green). The premise: true. The conclusion: true. The argument: false. In both their press release [1] and their article in Science [2] a UC Berkeley group suggest their (very nice) measurements of the Seebeck coefficient of individual organic molecules “offers the promise of efficient thermoelectric energy conversion devices” [from 2]. As far as I am aware these are indeed the first Seebeck measurements on individual organic molecules. And very nice measurements they are, resulting in S = +8.7, +12.9 and +14.2 microV/K for three different molecules. And I have to agree that organics are of some interest for thermoelectricity. They are inexpensive, come in infinite variety and often have attractively low thermal conductivity. Organic polymers, for example, can be better conductors than copper [3] and (others) can have Seebeck values over 1000 microV/K [4]. The trick, of course, is bringing these properties together in a single material, something which hasn’t happened yet. I noted all these things years ago [5,6]. As nice as the Berkeley experiment is, it doesn’t add much to the argument that organics might be efficient thermoelectrics. These three molecules have ZT values less than 0.005, 0.011 and 0.013 (assuming zero phonon thermal conductivity), values which compare poorly to ordinary thermocouple wires. So, the argument that this work brings cheap, efficient thermoelectrics based on organics closer to reality seems rather weak. Nice experiment. Good technique. Possibly an important new investigative tool. What more do you want? Egg in your beer? Spare me the breakthrough announcements until you actually have one. References 1. http://www.berkeley.edu/news/media/releases/2007/02/15_heatelectricity.shtml 2. Reddy, P., et al., Thermoelectricity in Molecular Junctions. Science, 2007: p. 1137149. Web: http://www.sciencemag.org/cgi/content/abstract/1137149v1 3. Kaiser, A.B., Metallic behaviour in highly conducting polymers. Synthetic metals, 1991. 45(2): p. 183-196. 4. Yoon, C.O., B.C. Na, and Y.W. Park, Thermoelectric Power and Conductivity of the Stretch-Oriented Polyacetylene Film Doped With MoCl 5. Synthetic Metals, 1991. 41(1-2): p. 41-43. 5. Vining, C.B., Thermoelectric Technology of the Future. 1994, ZT Services: ARPA Workshop on Fuel Cells/Advanced Batteries for Portable Power, La Jolla, CA USA. p. 30. 6. Vining, C.B. Thermoelectric Materials of the Future. in XII International Conference on Thermoelectrics, ICT93, Proceedings. 1994. Yokohama, Japan: Institute of Electrical Engineers of Japan, Tokyo.