The time of perovskites

31 10 2012

In the Aseanian Conference of dye-sensitized solar cells and organic solar cells, celebrated this week in Taipei, a number of important recent developments have been reported. The dye-sensitized solar cell, also known as Grätzel cell, in the most widely used and efficient configuration, is formed by nanostructured TiO2 as electron conductor, and organic dye as light absorber, and a redox electrolyte. It is believed that the liquid part is a weakness of the device, towards the realization of long lasting configurations for efficient conversion of solar light to electricity in the rooftop.

For many years there has been a search for a full solid version of the Grätzel cell, in which a solid absorber replaces the dye, and an organic or inorganic solid conductor makes the role of the liquid electrolyte.  The first suggestions in this direction came in late 1990s from Rolf Könenkamp, then at Hahn-Meitner Institut Berlin, and it was knwon as the Extremelly Thin Absorber solar cell. A few years later Gerardo Larramona, working at IMRA Europe, a japanese-owned company at Nice, France,  first tried the Sb2S3 solid absorber, with promising results,  in combination with inorganic p-type semiconductor CuSCN. Althouh this team reported 4% in a meeting in Jerusalem, they did not succeed to obtain  high efficiencies. Nonetheless, it has been recognized that such class of solid absorbers have very large absorption (extinction) coefficient and are likely candidates for complete solid cells of sensitized TiO2.  Using a variety of hole transporters, such as OMETAD and P3HT, the antimonium cell was improved to consistent efficiencies above 5% by work of the teams of Gary Hodes, Michael Grätzel and Sang Il Seok . This type of work has been, furthermore, complementary and strongly connected to the application of quantum dots as absorbers for nanostructured TiO2 solar cells, pioneered by Nozik, Zaban, Kamat, and many others. These concepts have been summarized in review articles by Prashant Kamat,  Thomas Dittrich et al, Arie Zaban et al, and Ivan Mora-Sero et al.

In 2009, a paper by Tom Miyasaka and coworkers showed 3.8% efficiency with a (CH3NH3)PbI3 perovskite compound. This result was very promising, and at this time, Nam-Gyu Park, a well known DSC scientist from South Korea that happened to have had perovskites as the subject of his pHD thesis, decided to develop this system. Recently in cooperation with M. Grätzel, Park and their coworkers presented in Nature a 9.7% efficiency based on the (CH3NH3)PbI3 absorber. Meanwhile Miyasaka joined forces with Henry Snaith, a young but tough-pushing DSC scientist at Oxford, and they reported a 10.7 % efficiency based on the perovskite, but without TiO2! It seems that the absorber perovskite layer on an insulating scaffold is sufficient to provide this power conversion efficiency without need for additional electron transport material. In fact, recently Lioz Etgar, Michael Grätzel, and their coworkers, showed that the (CH3NH3)PbI3 perovskite works well simply sandwiched between TiO2 and gold contacts, that is, without a specific hole conductor. Another major development is the report in Nature of a cell of CsSnI 2.95F0.05  exceeding 10% efficiency by a group of Northwestern University led by Mercouri Kanatzidis.

These developments were presented at the Aseanian Conference in Taiwan, where Seigo Ito reported for the first time a 5% efficiency in the  Sb2S3 cell with the hole conductor CuSCN. It seems that solid cells, especially those based on perovskites, offer a great potential for further development. However some participants in the Conference expressed concerns about reproducibility and stability of some of the reported devices. As in the past, we have to wait some time to see that other groups are able to reproduce these conversion efficiencies with the same materials, so that the results are robust and do not demand excepcional conditions of preparation, which is an important requisite for photovoltaic devices, that ultimately should be produced on a large scale.

Nevertheless it is clear that all solid Semiconductor Sensitized solar cells have experienced an impresive increase of efficiencies that follows the pace of all organic solid cells (see the status in may 2012 here). While the liquid cell has increased recently to 12.3% at 1 sun with the porphyrin dye and cobalt redox couple in the work of Eric Diau, Chen-Yu Ye, Michael Grätzel, and their coworkers, the solid cells with inorganic absorber seem to have entered an unstopable upward trend, as seen in the graph presented below.

The next opportunity to learn more of this topic is the 3rd International Conference on Semiconductor Sensitized and Quantum Dot Solar Cells, a nanoGe Conference which will take place from the 9th to the 11th of June 2013, in  Granada, Spain .

Papers cited:

“CdTe and CdS extremely thin absorber materials in An solar cell (ETA)”Siebentritt, S.; Ernst, K.; Fischer, C.-H.; Könenkamp, R.; Lux-Steiner, M. C.; 14Th European Photovoltaic Solar Energy Conference, 1997, Barcelona.,

Solid Nanostructured Solar cells made with nanocrystalline TiO2 films and absorber semiconductors, G. Larramona, A. Jacob, C. Choné, Nanoenergy Symposia : Semiconductor Sensitized Solar Cells Conference in Jerusalem, Israel, 2010, edited by A. Zaban (SEFIN, Castelló).

Hole Transport and Recombination in All-Solid Sb2S3-Sensitized TiO2 Solar Cells Using CuSCN As Hole Transporter, Pablo P. Boix, Gerardo Larramona, Alain Jacob, Bruno Delatouche, Ivan Mora-Sero, and Juan Bisquert, J. Phys. Chem. C (2011) 10.1021/jp210002c

High-Performance Nanostructured Inorganic−Organic Heterojunction Solar Cells. Chang, J. A.; Rhee, J. H.; Im, S. H.; Lee, Y. H.; Kim, H.-J.; Seok, S. I.; Nazeeruddin, M. K.; Grätzel, M., Nano Letters 2010, 10, 2609–2612.

From Flat to Nanostructured Photovoltaics: Balance between Thickness of the Absorber and Charge Screening in Sensitized Solar Cells, Pablo P. Boix, Yong Hui Lee, Francisco Fabregat-Santiago, Sang Hyuk Im, Ivan Mora-Sero, Juan Bisquert, and Sang Il Seok, acs Nano (2012) 10.1021/nn204382k

Quantum Dot Solar Cells. Semiconductor Nanocrystals as Light Harvesters. Kamat, P. V. The Journal of Physical Chemistry C 2008, 112, 18737–18753.

“Concepts of inorganic solid-state nanostructured solar cells” Dittrich, T.; Belaidi, A.; Ennaoui, A. Solar Energy Materials and Solar Cells (2011), 10.1016/j.solmat.2010.1012.1034.

“Quantum-Dot-Sensitized Solar Cells “Rühle, S.; Shalom, M.; Zaban, A. . ChemPhysChem 2010, 11, 2290 – 2304.

 Breakthroughs in the Development of Semiconductor-Sensitized Solar Cells Iván Mora-Seró and Juan Bisquert, J. Phys. Chem. Lett.20101, 3046–3052

Semiconductor Nanocrystal Quantum Dots as Solar Cell Components and Photosensitizers: Material, Charge Transfer, and Separation Aspects of Some Device Topologies. Hetsch, F.; Xu, X.; Wang, H.; Kershaw, S. V.; Rogach, A. L., The Journal of Physical Chemistry Letters 2011, 2, 1879-1887.

Organometal Halide Perovskites as Visible-Light Sensitizers for Photovoltaic Cells, Akihiro Kojima, Kenjiro Teshima, Yasuo Shirai, and Tsutomu Miyasaka J. Am. Chem. Soc.,(2009) 10.1021/ja809598r

Towards Printable Sensitized Mesoscopic Solar Cells: Light Harvesting Management with Thin TiO2 Films, T. Miyasaka, J. Phys. Chem. Lett. 2010, 2, 262–269.

Lead Iodide Perovskite Sensitized All-Solid-State Submicron Thin Film Mesoscopic Solar Cell with Efficiency Exceeding 9%, Hui-Seon Kim, Chang-Ryul Lee, Jeong-Hyeok Im, Ki-Beom Lee, Thomas Moehl, Arianna Marchioro, Soo-Jin Moon, Robin Humphry-Baker,Jun-Ho Yum, Jacques E. Moser, Michael Grätzel and Nam-Gyu Park, Nature Scientific Reports, 2, 591 (2012) 10.1038/srep00591

Efficient Hybrid Solar Cells Based on Meso-Superstructured Organometal Halide Perovskites, Lee MM, Teuscher J, Miyasaka T, Murakami TN, Snaith HJ, Science (2012) Oct 4

All-solid-state dye-sensitized solar cells with high efficiency, In Chung, Byunghong Lee, Jiaqing He, Robert P. H. Chang and  Mercouri G. Kanatzidis, Nature 485, 486–489 (2012)

“Porphyrin-Sensitized Solar Cells with Cobalt (II/III)Based Redox Electrolyte Exceed 12 Percent Efficiency” Yella, A.; Lee, H.-W.; Tsao, H. N.; Yi, C.; Chandiran, A. K.; Nazeeruddin, M. K.; Diau, E. W.-G.; Yeh, C.-Y.; Zakeeruddin, S. M.; Grätzel, M. . Science 2011, 334, 629-634.

“Mesoscopic CH3NH3PbI3/TiO2 Heterojunction Solar Cells” Lioz Etgar,  Peng Gao, Zhaosheng Xue, Qin Peng, Aravind Kumar Chandiran, Bin Liu, Md. K. Nazeeruddin and Michael Grätzel, J. Am. Chem. Soc. 2012, 134, 17396−17399

The famous scheme of an Extremelly Thin Absorber all solid nanostructured solar cell, probably made by Rolf Könenkamp (?)

Progress of efficiency of hybrid and organic solar cells. Graph courtesy of Tsutomu Miyasaka.

Perovskite people: Nam-Gyu Park, Mercouri Kanatzidis and Tom Miyasaka

Nam-Gyu Park, Tom Miyasaka, the author of this blog, Mercouri Kanatzidis, Seigo Ito, and Peter Chen, at the 7th Aseanian Conference of DSC-OPV.

Advances in impedance spectroscopy of solar energy conversion devices

24 10 2012

Ramon Llull: From the Ars Magna to Artificial Intelligence

12 10 2012

Ramon Llull: From the Ars Magna to Artificial Intelligence

Book edited by

Alexander Fidora
Carles Sierra


The lay philosopher and theologian Ramon Llull (1232–1316), born
in Mallorca, is undoubtedly a prominent figure within European
thought. However, the exact position he occupies within the cultural
horizons of his period, on the one hand, and the intellectual
legacy he bequeaths to the present day, on the other, are issues
often immersed in controversy. This situation derives, in part,
from the protean multiplicity of his writings, manifested by an
impressive variety of forms, styles and subject matter, Llull having
composed some 280 works in both Catalan and Latin (as well
as reputedly in Arabic).
Running throughout his immense oeuvre, nevertheless, is a
leitmotif that enables one to arrive at an overall, if not unitary,
view, that leitmotif being the Ars lulliana or Lullian Art: a
philosophico-theological system that makes use of common basic
concepts from the three monotheistic religions of its day, subjecting
them to discussion with a view to convincing Muslims (and
Jews) via rational argument of the truth of the Christian mysteries
of faith. By revising his Art and extending it to all fields of
human knowledge, Ramon Llull succeeded in creating a universal
science, based on the algebraic notation of its basic concepts
and their combination by means of mechanical figures. As a matter
of fact, Llull not only presented his system to the masters of the
University of Paris as well as to the Pope, but he undertook several
missionary trips to North Africa in order to put his Ars into
practice disputing with Muslims in the market place in Bejaia and
other cities.
From a more abstract point of view, Llull’s combinatorial Art
can be described as a process of elementary analysis and of reconstruction.
On the one hand, it resolves the historical religions into
their most primitive elements; on the other, it represents these
elements by letters (from B to K), in order to recombine these
letters and the elements of the different religions that they designate
until, through these combinations, a vision of the world is
reached that is as consistent as possible: this will correspond to
truth. Undoubtedly, this process which Llull applied to all kinds
of question —not just religious controversies— is a key ingredient
of modern thought. One only has to think of Gottfried Wilhelm

Leibniz’s characteristica universalis: thus, in his Dissertatio de arte
combinatoria, in 1666, the young Leibniz, clearly inspired by Llull,
had already outlined the project of a reconstruction of the whole
of reality based on a definite number of basic notions. Leibniz
criticizes the basic notions of the Lullian “alphabet” as too limited
and proposes another alternative and broader alphabet. In
contradistinction to Llull, Leibniz does not represent these basic
notions with letters but rather uses numbers. Thus, the basic notion
of “space” is represented by the number 2, the basic notion of
“between” by the number 3, and the basic notion of “the whole”
by the number 10. Consequently, according to Leibniz, a complex
concept such as, for instance, “interval” can be formulated as
2.3.10, that is, “space between the whole”. Leibniz was convinced
that in this way all questions could be reduced to mathematical
problems and that, in order to solve any problem, we only have
to set about calculating. This is the meaning of Leibniz’s famous

It is through Leibniz that Llull’s influence also became decisive
for more recent developments such as formal logic, as developed
by Gottlob Frege in the late 19th century. According to
Frege, Leibniz’s characteristica, in its later evolution, limited itself
to different fields, such as arithmetic, geometry, chemistry
and so on, but did not become universal as Leibniz, in fact, had
wished. This is why Frege, in his famous Begriffsschrift from 1879,
intended to create an elementary language that would unify the
different formal languages which, after Leibniz, had been established
in the different natural sciences. This language developed
into the formal logic that until now has dominated the philosophical
discourse and which was an important step in the journey
towards the creation of computing languages. What characterizes
this kind of logic is its formal notation, using variables and
symbols to represent the different logical propositions and operations.
Based on this notation, Frege developed the so-called logical
calculus. Although the language reached by this formal logic
differs from that of the Art, Llull can be considered as the forerunner
of this project, insofar as in his thought one can already find
the idea of an elementary language that follows logical rules and
uses variables while operating with the principle of substitution
of these variables.

The book

See also an article by Fernando Cuartero

El Mapa i el Territori: Una novel·la

6 10 2012

El Mapa i el Territori

Michel Houellebecq

Esta novel·la de Houellebecq és un plaer de llegir, és molt entretinguda. Sembla que després de moltes dècades d’experimentació i destrucció els autors francesos tornen a una estructura clàssica de novel·la. A banda de la pura i sòlida narrativa el llibre també conté dimensions conceptuals molt interessants. Es planteja una reflexió sobre temes polítics i socials, heretada del tipus d’anàlisi del marxisme decimonònic, que examina el món actual. El llibre analitza la producció d’objectes en el nostre món, el combat entre la irreductible necessitat de ser singular i la producció en massa. El llibre s’endinsa en una espècie de costumisme, un catàleg dels oficis, però això no es fa directament, sinó narrant la vida de l’artista que agafa este programa i el fa seu, amb gran èxit, catalogant el territori humanitzat, des del punt de vista del productor de mapes, o les professions que formen el engranatge de la societat. Els personatges principals, són persones especials, manquen de qualsevol dimensió afectiva ni família ni empatia, i es dediquen per complet a la producció, del sublim, com una ordre, com un imperatiu que els arrabassa. Existeix una dimensió moral, el Bé, i com diu, “ser artista era per damunt de tot, ser algú sotmès. Sotmès a missatges misteriosos, imprevisibles, que s’havien de qualificar, a falta de res millor i en absència de tota creença religiosa, d’intuïcions; missatges que s’imposaven d’una manera imperiosa, categòrica, sense permetre cap possibilitat de sostreure-s’hi, si no era perdent tota noció d’integritat respecte d’un mateix.” És una bona descripció també de la força motriu de moltes creacions científiques, una convicció que fa estar a voltes molts anys perseguint un rastre, que s’albira a mitges, per la pura convicció personal que hi ha alguna cosa important, i es fa per gust de fer-ho, sovint, amb la puresa de l’actitud d’aquell que arrisca tot per un ideal, i així, “mai no decideixes tu mateix l’escriptura d’un llibre.” Però en el llibre de Houellebecq, la creació que s’examina no es única, són productes o produccions que involucren les masses “els diferents engranatges que intervenen en el funcionament d’una societat”, com ara complexes residencials de vacances, per exemple, i en particular, els protagonistes mostren una fascinació especial per la gran distribució, parlen dels hipermercats, també podria ser Zara. Perquè “som en un punt en què l’èxit en termes de mercat justifica i dóna validesa al que siga, substitueix totes les teories, ningú no és capaç de veure més enllà, absolutament ningú.” Amb tot, el cas paradigmàtic, és el de Steve Jobs, el creador dedicat a la seua intuïció totalment, sense compromisos, buscant unidimensionalment el resultat que ha somniat, però a la fi, el producte es repetirà milions de voltes, i no molt mes tard, acabarà en una pila de ferralla. La qüestió és si es possible una representació artística del món, si la representació és un dispositiu emocional o racional. I aixina el tema central és el Déu, el creador no d’una obra única com el artista sinó de tota la complexitat de la societat, el creador que després pot admirar tota la cadena de complexes relacions. Com Steve Jobs, sovint considerat el més proper a un Déu que podem tindre en este temps, que movilitza immensos recursos per a complir els seus desitjos, que marquen com viuran tots els altres humans. I així en la representació de Jobs “en la mirada li brillava la flama que no és només la dels predicadors i els profetes, sinó també la dels inventors.” El creador necessita una motivació essencial, odi, o fins i tot la fam. L’artista, no te cap vida privada, sols vol “donar compte del món” i res més. I junt amb la creació, ve la seua degradació i la mort, que és el altre gran tema del llibre. Ens dona una orientació de la dimensió del Bé en la dedicació profundament honesta en una activitat, relacionada amb una noció profunda de la veritat, “sense ser empesos per l’incentiu del guany, sinó per alguna altra cosa, als ulls d’un home modern, molt més vaga: l’amor a Déu, en el cas dels monjos, o simplement l’honor de la funció.” Però Houellebecq també és capaç de mostrar el revers de la trama, el Mal, i ho fa.

Com he dit, el llibre es llig amb fruïció, però fins a quin punt estes dimensions ideològiques enfosqueixen la presentació de l’experiència vital que seria pròpia de la novel·la? No es sap si són els personatges, moguts per la realitat que els envolta i les decisions que prenen en conseqüència, els que mostren el programari, o si el llibre es mou en el camp del assaig. És un punt que no tinc gens clar, però en tant que la representació és, declaradament, el tema de la novel·la mateixa, pot ser totes estes consideracions reflexives que compliquen la vida del personatges són una construcció deliberada del autor, i el lector es veu envoltat en el joc de miralls. Això ho haurà de determinar cada u, llegint esta magnífica novel·la.