
New solar cell material achieves almost 100% efficiency - nickb
http://www.tgdaily.com/html_tmp/content-view-39807-113.html
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DaniFong
Damnit, journalism. How on earth did they get this:

"Researchers at Ohio State University have accidentally discovered a new solar
cell material capable of absorbing all of the sun's visible light energy. The
material is comprised of a hybrid of plastics, molybdenum and titanium. The
team discovered it not only fluoresces (as most solar cells do), but also
phosphoresces. Electrons in a phosphorescent state remain at a place where
they can be "siphoned off" as electricity over 7 million times longer than
those generated in a fluorescent state. This combination of materials also
utilizes the entire visible spectrum of light energy, translating into a
theoretical potential of almost 100% efficiency. Commercial products are still
years away, but this foundational work may well pave the way for a truly
renewable form of clean, global energy."

From this:

"Oligothiophenes incorporating MM quadruple bonds have been prepared from the
reactions between Mo2(TiPB)4 (TiPB = 2,4,6-triisopropyl benzoate) and
3′,4′-dihexyl-2,2′-:5′,2″-terthiophene-5,5″-dicarboxylic acid. The oligomers
of empirical formula Mo2(TiPB)2(O2C(Th)-C4(n-hexyl)2S-(Th)CO2) are soluble in
THF and form thin films with spin-coating (Th = thiophene). The reactions
between Mo2(TiPB)4 and 2-thienylcarboxylic acid (Th-H),
2,2′-bithiophene-5-carboxylic acid (BTh-H), and
(2,2′:5′,2″-terthiophene)-5-carboxylic acid (TTh-H) yield compounds of formula
trans-Mo2(TiPB)2L2, where L = Th, BTh, and TTh (the corresponding
thienylcarboxylate), and these compounds are considered as models for the
aforementioned oligomers. In all cases, the thienyl groups are substituted or
coupled at the 2,5 positions. Based on the x-ray analysis, the molecular
structure of trans-Mo2(TiPB)2(BTh)2 reveals an extended Lπ-M2δ-Lπ conjugation.
Calculations of the electronic structures on model compounds, in which the
TiPB are substituted by formate ligands, reveal that the HOMO is mainly
attributed to the M2δ orbital, which is stabilized by back-bonding to one of
the thienylcarboxylate π * combinations, and the LUMO is an in-phase
combination of the thienylcarboxylate π * orbitals. The compounds and the
oligomers are intensely colored due to M2δ–thienyl carboxylate π * charge
transfer transitions that fall in the visible region of the spectrum. For the
molybdenum complexes and their oligomers, the photophysical properties have
been studied by steady-state absorption spectroscopy and emission
spectroscopy, together with time-resolved emission and transient absorption
for the determination of relaxation dynamics. Remarkably, THF solutions the
molybdenum complexes show room-temperature dual emission, fluorescence and
phosphorescence, originating mainly from 1MLCT and 3MM(δδ* ) states,
respectively. With increasing number of thienyl rings from 1 to 3, the
observed lifetimes of the 1MLCT state increase from 4 to 12 ps, while the
phosphorescence lifetimes are ≈80 μs. The oligomers show similar photophysical
properties as the corresponding monomers in THF but have notably longer-lived
triplet states, ≈200 μs in thin films. These results, when compared with
metallated oligothiophenes of the later transition elements, reveal that
M2δ–thienyl π conjugation leads to a very small energy gap between the1MLCT
and 3MLCT states of <0.6 eV."

<http://www.pnas.org/content/105/40/15247.short>

The discovery of phosphorescent dual emission is a striking and important one,
but there are dozens of hurdles still to create a solar cell, any one of which
might be a nail in the coffin for the material. For example, just because some
of the electrons end up in a triplet state doesn't mean all of them will:
they've measured the singlet states as rapidly decaying, and therefore they'll
have essentially the same trouble will harvesting them as other photovoltaics
have. Furthermore, one won't be able to harvest all the energy from the
visible spectrum even in principle: at a high level because of the second law
of thermodynamics, and in the specific because the material will radiate as
well.

