Perovskite solar cells ramping up efficiencies

30 05 2013

This entry was written in part by Victoria González

Efficient solar energy conversion using solar cells requires materials that absorb in a broad spectral range, from visible to near infrared, to harvest most of the solar photons, as well as with the capability to convert effectively the incident light into free charges that produce electrical current and voltage. High crystalline materials, with good carrier mobility reduce the energetic costs associated to the electron/hole separation and charge extraction. However these technologies stumble with high cost fabrication procedures, that make use of vacuum based or high-temperature processing, limiting its commercial application. Issues of cost and fragility have impeded the availability of low cost solar energy that is much needed to replace fossil fuels as the primary energy source.

On the other side, third generation of photovoltaic devices, dye sensitized solar cells (DSCs) and organic photovoltaics, need simpler procedures what reduces significantly the cost of manufacturing processes. But these technologies employ a combination of amorphous and disordered materials, so the energy costs associated to extract free charges represent a fundamental loss and a main limitation to high efficiency systems.

Currently, the recently emerged perovskite structure based materials is revolutionizing the photovoltaic field,  and, as very recent studies demonstrate, they can reach a trade off between broad spectral absorption range, as well as high crystalline that induces efficient charge extraction reducing energetic costs, with simple and low cost fabrication techniques.

Mitzi and co-workers have reported the synthesis of several organometalic perovskites based in lead halide materials. Different structures 2D and 3D spatial distributions were developed and its suitable opto-electronic proprieties were exploited in the fabrication of transistor and light emitting diodes (D.B. Mitzi et al., Nature, 1994, 369,467; K. Chondroudis, Chem Mat., 1999, 11, 3028). More recently, Miyasaka et al. (A. Kojima, J. Am. Chem. Soc., 2009, 131 (17), 6050) demonstrated the potentiality of methyl ammonium lead halide perovskites in sensitized solar devices based on TiO2 mesostructure photoanodes.  Although it was during last year, 2012, when the boom of perovskites materials took place and the different contributions of Nam-Gyu Park, Michael Grätzel, and Henry Snaith have highlighted the great potential of these materials towards the development of efficient solid state photovoltaic devices (H.S. Kim, Sci. Rep. 2012, 2, M.M. Lee, Science, 2012, 338, 643; J. Ball, Energy & Environmental Science, 2013, DOI:10.1039/C3EE40810H). Two weeks ago, a conference report by Michael Grätzel showed a 14.14% efficient certified cell of this class, which put the perovskite solar cells ahead of several traditional technologies.

On wednesday 28 at EMRS meeting in Strassbourg, Henry Snaith reported a major step in the evolution of the perovskite solar cells. He reported the construction of a  15% cell with thin-film  structure (TIO2/CH3NH3PbI3/OMeTAD) . For the crystal growth of vapor deposition of CH3NH3PbI3 were employed spin coating and vapor deposition techniques.  Higher crystallinity was obtained for films grown by vapor deposition technique that has provided the record efficiency of 15.35% (Jsc= 21 mA/cm2, Voc= 1.07 and FF= 0.67) for this material. This result highlights the potentiality of these materials that have emerged as a competitive technology in thin solar cell fabrication, which can be processed with solution-based techniques at low-temperatures, leading to the least expensive technology.

The new result by Snaith is also significant in that there seems to be no nanostructure assisting charge separation in the absorber film, but just a homogeneous film with selective contacts, the TiO2 compact layer for electrons and organic hole conductor Spiro-OMeTAD and gold contact for holes. Thus the perovskite solar cells start to move to the class of ordinary thin films, as amorphous silicon, CdTe, CIGS, and other, that already form competitive technologies in the market. Nonetheless, the organic hole conductor is confirmed as a significant component for high efficiency photovoltaic action, thus the perovskite solar cell still remains into the family of hybrid organic-inorganic solar cells.

A range of significant questions open up right now, concerning the significance of crystallinity,  the relationship between efficiency and stability with film deposition method, that will impact the cost effectiveness of the technology. No doubt these issues will be addressed by a broad research community, and probably this will happen rapidly. Snaith commented that with the ramping up from 10 to 15% in six months, clearly 20% could be on sight ahead, then perovskite solar cell will emerge as a real major player for the cheap production of solar energy on a real large scale. He’s probably right.

Henry Snaith and JB at EMRS after-dinner. Picture by Seigo Ito

Advertisements




Austerity and Economic Growth

19 05 2013

Paul Krugman

How the Case for Austerity has Crumbled

The New York Review of Books, June 6, 2013

 

image

The Figure shows what happened to a selection of European nations (each represented by a diamond-shaped symbol). The horizontal axis shows austerity measures—spending cuts and tax increases—as a share of GDP, as estimated by the International Monetary Fund. The vertical axis shows the actual percentage change in real GDP. As you can see, the countries forced into severe austerity experienced very severe downturns, and the downturns were more or less proportional to the degree of austerity.

Three years after the turn to austerity,  both the hopes and the fears of the austerians appear to have been misplaced. Austerity did not lead to a surge in confidence; deficits did not lead to crisis. But wasn’t the austerity movement grounded in serious economic research? Actually, it turned out that it wasn’t—the research the austerians cited was deeply flawed.





The evolution of mesoscopic solar cells

8 05 2013

At HOPV 13 Conference Henry Snaith presented interesting ideas about the exciting devlopment of mesoscopic solar cells based on perovskite absorbers. Snaith was the one to have the idea to remove the TiO2 while preparing the mesoscopic solar cells, using instead mesoporous alumina , where electron cannot be injected because of energetic reasons. These results where published in the Science paper with Miyasaka last year. Today Henry proposed the view that there is a major change on the field of mesoscopic solar cells, which could evolve to either thin film or mesoscopic heterojunction. Thefore a number of questions appear now, and will be studied in the near future together with the outstanding results of Grätzel’s group communicated below. Since the perovskite looks an efficient transporter of electrons and holes with a reasonable lifetime, is TiO2 needed or important? More generally, is a separation into electron and hole conductors needed, or just selective contacts at the electrodes? How thick will be the perovskite absorber, will it form a thin layer covering a mesostructure, or a thick layer that carries both electrons and holes?

The changes of mesoscopic solar cells:

DSC
solid DSC
ETA
perovskite MSSC, with or without TiO2

future:
pin thin film?
porous perovskite pn junction?

Henry Snaith at HOPV 13

Henry Snaith at HOPV 13





La llengua catalana o que

8 05 2013

Alla pel 1994 estavem redactant els estatuts de la Universitat Jaume I i es va presentar el problema de denominar la llengua dels valencians. Veniem d’una epoca on hi havia hagut enfrontaments socials dramatics per l’assumpte dels simbols del Pais Valencia, la denominacio, la llengua, i altres coses semblants. Estes guerres de simbols, adquireixen una virulencia sols comparable a les guerres de religio. Recorde que viatjavem pel maestrat amb una amiga meua originaria de Iran, i veiem els indicadors de carretera borrats amb spray negre de forma que al final no ens podiem orientar. Una practica on tots perden, ella no en donava credit que la gent tapara els cartelons.
En fi, la llengua dels valencians no es catalana en realitat, ja que la llengua no es de ningu, es pot dir que pertany a valencians, catalans, mallorquins i a moltes persones mes que l’aprecien i la parlen. Pero el nom de la llengua es la llengua catalana, es que es diu aixi i discutir-ho es una perduda de temps util i a mes dona lloc a arguments de tipus hortera. Com el nom de la llengua es refereix a l’estructura i continguts d’este sistema linguistic, es una questio d’estudi de gent que es dedica a estes coses, es un assumpte empiric en realitat, per aixo, vam decidir escriure en els estatuts, que la Universitat hauria de fer una defensa particular de la llengua propia dels valencians, que academicament es diu llengua catalana. Ara he vist que esta simple frase va comensar una batalla legal entre diversos ambits institucionals i politics que ha durant fins ara, quasi 20 anys. Sembla que finalment es pot gastar esta afirmacio sobre la meua llengua que per a mi es una tautologia: academicament llengua catalana. Per tant podem dir que parlem valencia, com s’ha fet sempre, sense problemes, pero denominem catala al sistema linguistic complet i formal, que pots aplicar en literatura, ciencia, en allo que vullgues.
Tot aso es un poc complicat, la veritat, he comentat este assumpte amb un bon amic que coneix millor el tema, i em diu que efectivament, moltes coses es van tancar malament sobre el nostre pais, pero què podem esperar d’un país, en el que, tal i com cantava Raimon:

“Al meu país la pluja no sap ploure:
o plou poc o plou massa;
si plou poc és la sequera,
si plou massa és la catàstrofe.
Qui portarà la pluja a escola?
Qui li dirà com s’ha de ploure?
Al meu país la pluja no sap ploure.”





Perovskite pigment solar cells boost power conversion efficiency

7 05 2013

It’s not usual that we see a world record announced at a Conference. Today at HOPV 13 meeting in Seville Michael Grätzel shows a 14.14% power conversion efficiency certified solar cell made at EPFL.

The new solar cell has entered the official tables of efficiency records published by NREL. This results puts the mesoscopic inorganic solar cells ahead in the race for high efficiencies .

13 05 efficiency 3

13 05 efficiency

.

Michael Grätzel

Michael Grätzel





HOPV13 Seville

6 05 2013
Juan Bisquert, Thuc-Quyen Nguyen. René Janssen

Juan Bisquert, Thuc-Quyen Nguyen. René Janssen

Coffee break

Coffee break

Plenary Conference

Plenary Conference

Sir Richarrd Friend at Seville HOPV13

Sir Richard Friend at Seville HOPV13

Invited speakers and organizers

Invited speakers and organizers

Satosi Uchida and JB at HOPV 13 Conference

Satosi Uchida and JB at HOPV 13 Conference

Antonio Fachetti at HOPV

Antonio Facchetti at HOPV 13

Peter Bäuerle at HOPV 13

Peter Bäuerle at HOPV 13

Emilio Palomares at HOPV 13

Emilio Palomares at HOPV 13

 

s





Writing scientific papers

3 05 2013

How to Make Your Next Paper Scientifically Effective

Prashant Kamat * (Deputy Editor) ,
University of Notre Dame, Notre Dame, Indiana 46556, United States
George C. Schatz (Editor-in-Chief)
Northwestern University, Evanston, Illinois 60208, United States
J. Phys. Chem. Lett., 2013, 4 (9), pp 1578–1581
DOI: 10.1021/jz4006916
Publication Date (Web): May 2, 2013
Copyright © 2013 American Chemical Society