Moving continent is a great source for procrastination: filling boxes, emptying boxes, rearrangements and reorganizations galore. Another pair of transatlantic flights (this time to the IEEE Photovoltaics Specialist Conference in Philadelphia) will provide the internet-free time I need.

Wolfram Alpha is a strange one. Nice for graphing whatever function comes into your mind, but it gets confused a little too often for its own good. The comparing compounds feature is fun, and I imagine it would be quite useful for a synthetic chemist. I could see it morphing into a chemistry version of Top Trumps; a potential tool for hooking ten year olds into the magic of the periodic table.

In other developments, last week the head of Shell’s renewable energy wing stepped down. This is probably not too surprising considering that Shell recently announced their abandonment of research and development of solar and wind power. Not satisfied with pillaging the Irish coast line while charging plenty for it, a company that pulled in $26 billion of profit last year cannot afford to spend a little on harnessing our most abundant energy sources. I really hope I live to see the complete collapse of oil companies.

Finally, the last episode in Season Two of Breaking Bad is on tonight. An incredibly intense twelve episodes so far. It does of course have some lighter moments, such as how to make a DIY Faradic battery using acid and loose change to kick-start a dead van in a desert, but overall, this is definitely the best show on TV right right now.

Early 20th century Irish literature isn’t the first place you’d go to look for thought provoking scientific absurdism*, but The Third Policeman is such a find. A haunting novel, seeping with dark humor throughout.

We all know the Michelson–Morley experiment; in an attempt to prove the existence of ether, they developed an elegant way to measure the speed of light with mirrors. In The Third Policeman, the protagonist’s philosophical guru De Selby, took this to new extremes. After the realization that we when look in a mirror, we are always seeing ourselves in the past, he constructed a ‘familiar arrangement of parallel mirrors’ until he saw ‘the face of a beardless boy of twelve’. Unfortunately, he couldn’t regress further owing to ‘the curvature of the earth and limitations of the telescope’. We are also treated to arguments for why movement doesn’t exist, that night is a congregation of black air that asphyxiates us into sleep, and why quantum theory implies you shouldn’t ride your bicycle too often. An essential read.

Moving away from fiction, the e-Journal of Surface Science and Nanotechnology just published the proceedings from last year’s ICSFS conference. Peer reviewed and free access. Our contribution was Li/H in MgO.

*Although we do have Joyce to thank for “Three quarks for Muster Mark!”.

(APS 2009) Pittsburgh is an interesting place. The most striking part of downtown is the series of yellow steel bridges crossing the river; Pittsburgh steel. One is named the Andy Warhol bridge, although it was built at the start of the 20th century, but now leads across towards the Andy Warhol museum; the latter being a highlight of a trip to the city.

The massive convention centre was well able to handle the 7000 strong crowd of physicists, even if the local restaurants had a tough time keeping up. One server remarked that she may be able to pay off her car loan thanks to the crowds this week. Judging from the number of closed premises around downtown, the conference was a welcomed boost.

I doubt I’ll bother coming back to the APS often when I leave the US. It is not very well organized at all. There are far too many talks, too many sessions and too few posters. This year especially felt like a cattle show. If you keep up with recent publications in PRL and PRB, many of the talks, consisting of brief ten minute snapshots, offer nothing new. It’s sad that clashing egos end up becoming the centre of attention, and not new science. I think the MRS has the right idea of providing selective, focused sessions while still catering to a broad audience.

Cheaper solar cell materials = more solar cells = decrease in fossil fuel dependence. Good. A recent paper from the new ACS environmental journal caught my attention on this very topic: “Materials Availability Expands the Opportunity for Large-Scale Photovoltaics Deployment”. It even got a write up in Chemistry World: “Analysis hints at solar energy alternatives”. Their findings are nice, if a little overly optimistic, but first some context...

Silicon, being an indirect band gap semiconductor, is at an obvious disadvantage for solar cells: you need thick films to have enough light absorption to generate significant photocurrents. The use of direct band gap semiconductors enables thin-film solar cells, costing less energy (and material) to produce. Since the 1970’s CdTe and Cu(In,Ga)Se2 have been two thin-film prototype absorbers, but they both suffer from their fair share of idiosyncrasies. For an ideal case, the (open-circuit) voltage you can get from a single-junction absorption material will be close to the value of the band gap. To approach this, you will need to have some very nice epitaxial thin films and a well behaved system. Generally the performance is much less than you’d expect, e.g. Cu(In,Ga)Se2 can be tuned to have an almost ideal band gap of around 1.3 eV, while the voltage you get out is on the order of 600 meV. This could be through a combination of (deep level) defects which can pin the Fermi energy where you don’t want it, or as in the case of most Cu based materials, a number of competing phases and defect complexes.

Back to the paper in question: “Twelve composite materials systems were found to have the capacity to meet or exceed the annual worldwide electricity consumption”. CuO, FeS2 and Zn3P2 are the ‘unconventional’ candidates highlighted in the abstract. Unfortunately, you have no hope of extracting voltages on the order of the band gaps, and being modest, you could easily decrease their expected efficiencies by a factor of two. Looking a bit deeper:
• CuO, with the highly correlated Cu 2+ d9 cation, is an indirect band gap (1.4 eV) Mott–Hubbard insulator (i.e. it’s highly resistive). Probably not the best bet for next generation solar cells.
• Zn3P2 appears more promising (if a little old). While it also has an indirect band gap (1.4 eV), it is intrinsically p-type and has reasonable carrier mobility.
• FeS2 combines a low band gap (1 eV) with some decent looking transport properties. However, looking below the surface, it has been tried and tested. 2.8 % efficiency won’t replace Si anytime soon. The study does raise one strong point: we really need to consider component cost and availability when designing new materials, especially for any energy related applications.