Bous a la mar

24 03 2015

Bous a la mar en Denia, late 70s

bous





Smart girl scientists in Iran

13 03 2015

60% of Iran scientists are women. Competent, smart, ambitious. They travel abroad and know the modern mind. But will they find a ceiling if going up in the ranks?

Several lady scientists and JB at Asian Nano Forum Congress 2015, Kish Island, Iran

Several solar cell scientists (Raheleh Mohammadpour, Leila Shooshtari, two ladies, Sara Rahimnejad and JB) at Asian Nano Forum Congress 2015, Kish Island, Iran

 





Best Practices in Perovskite Solar Cell Efficiency Measurements.

6 03 2015
Jeffrey A. Christians, Joseph S. Manser, and Prashant V. Kamat
J. Phys. Chem. Lett. 2015, 6, 852–857
DOI: 10.1021/acs.jpclett.5b00289

This Viewpoint brings to light some of the issues pertaining to perovskite solar cells and provides the field with best practices for measuring and reporting perovskite solar cell performance.




Political corruption impedes innovation in science and technology

26 02 2015

In Mediterranean countries like Spain we are very used to corruption in the public authority. In recent years, when economic crisis brought about the scarcity of resources, many specific situations of corruption that previously were generally ignored have emerged to the public domain. It has become widely acknowledged that while a substantial part of citizens live with meager means, close to poverty, a vast deviation of public resources occurred to specific private or even personal interest. This realization has caused great scandal and maybe there will be some political upheavals as a result of this. For example the members of governing board of former public bank CajaMadrid (transformed into Bankia), were using limitless black credit cards for personal needs, while the bank they managed costed a finnancial rescue of some 30,000 million euro (yes, 40 billion dolars), that all citizens have had to suport, willing or not. The expenses of this particular issue are just a few milions but they are highly representative of the operation of Spanish politics, since all parlamentary parties were involved in the abuse, and only 3 out of 100 board members refused to use the irregular credit cards.

Indeed it must be said, that this problem has been known by everybody more or less. Historically these attitudes were regarded quite normal. Corruption is the normal way of doing politics in a dictatorships, as the one Spain enjoyed between 1939 and 1975.  We thought democracy would cretae cleaner politics with time, but this has not happened. In afacts these ways were easily tolerated in the recent decades, and people that commited these abuses was routinely reelected for office. The widspread belief was that anyone that you put in the office will do it, so we have to leave up to it. And when it is your turn, seize the day…

But now, beyond the natural reaction of indignation that the massive scale of corruption is producing, many people is recognizing that widespread corruption is a real cancer to the res publica (the public domain), that substantially degrades many aspects of life, not only moraly but also practically. Indeed corruption creates deep malfunctions in the mechanisms of a modern society. For example, it has become widespread in Spain to talk about “revolving doors”, which means that prominent politicians, when leaving office, become advisors of the megacompanies in the country (energy, telecom, …), so that they help with their connections to produce benign legislation and flavourous contracts. Such companies are few and they manage a lot, so a subtantial part of the economy is controlled by connections between a few partnerships of politicians and company managers. Often invoked benefits of free market and competition are just an ideal that is far from suceeding . Naturally all extra costs, and the loss of potential progress by less connected entrepeneurs, are finally supported by all citizens that barely have a chance to know what is going on behind the scene, as the whole system of public life is implicated in these ways. Undoubtedly this system impoverishes the economic and productive power of the citizens, in favor of the blessed casta.

While these debates are taking a growing share of public discussions, they are open to opinion and mood and the amount of damage is difficult to quantify. However, an excellent paper in Nature has done just this, which is to show the strong correlation between the level of control of corruption and the innovation in science and technology that the country actually produces. Just have a look at it.

NATURE | COMMENT

Corruption: Good governance powers innovation

Alina Mungiu-Pippidi

18 February 2015
nature_Government-corruption_19.02.15




Superior Photovoltaic Properties of Lead Halide Perovskites: Insights from First-Principles Theory

19 02 2015

The Journal of Physical Chemistry C is presenting a series of Feature Articles by key scientists about the fundamental properties of Hybrid Organic-Inorganic Halide Perovskites.

 

Superior Photovoltaic Properties of Lead Halide Perovskites: Insights from First-Principles Theory

Wan-Jian Yin , Tingting Shi , and Yanfa Yan
J. Phys. Chem. C, Article ASAP
DOI: 10.1021/jp512077m
Organic–inorganic methylammonium lead halide perovskites have recently emerged as promising solar photovoltaic absorbers. In this Feature Article, we review our theoretical understanding of the superior photovoltaic properties, such as the extremely high optical absorption coefficient and very long carrier diffusion length of CH3NH3PbI3 perovskites through first-principles theory. We elucidate that the superior photovoltaic properties are attributed to the combination of direct band gap p–p transitions enabled by the Pb lone-pair s orbitals and perovskite symmetry, high iconicity, large lattice constant, and strong antibonding coupling between Pb lone-pair s and I p orbitals. We show that CH3NH3PbI3 exhibits intrinsic ambipolar self-doping behavior with conductivities tunable from p-type to n-type via controlling the growth conditions. We show that the p-type conductivity can be further improved by incorporating some group IA, IB, or VIA elements at I-rich/Pb-poor growth conditions. However, the n-type conductivity cannot be improved under thermal equilibrium growth conditions through extrinsic doping due to the compensation from intrinsic point defects.

 





Principles of Chemical Bonding and Band Gap Engineering in Hybrid Organic-Inorganic Halide Perovskites

14 02 2015

The Journal of Physical Chemistry C is presenting a series of Feature Articles by key scientists about the fundamental properties of Hybrid Organic-Inorganic Halide Perovskites. Here is the first one.

Principles of Chemical Bonding and Band Gap Engineering in Hybrid Organic-Inorganic Halide Perovskites

Aron Walsh
J. Phys. Chem. C, Just Accepted Manuscript
DOI: 10.1021/jp512420b
The performance of solar cells based on hybrid halide perovskites has seen an unparalleled rate of increase, while our understanding of the underlying physical chemistry of these materials trails behind. Superficially, CH3NH3PbI3 is similar to other thin-film photovoltaic materials: a semiconductor with an optical band gap in the optimal region of the electromagnetic spectrum. Microscopically, the material is more unconventional. Progress in our understanding of the local and long-range chemical bonding of hybrid perovskites is discussed here, drawing from a series of computational studies involving electronic structure, molecular dynamic and Monte Carlo simulation techniques. The orientational freedom of the dipolar methylammonium ion gives rises to temperature dependant dielectric screening and the possibility for the formation of polar (ferroelectric) domains. The ability to independently substitute on the A, B and X lattice sites provides the means to tune the optoelectronic properties. Finally, ten critical challenges and opportunities for physical chemists are highlighted.




Depolarization kinetics of perovskite solar cells in slow time regime

2 02 2015

Cooperative kinetics of depolarization in CH3NH3PbI3 perovskite solar cells

Luca Bertoluzzi,a   Rafael S. Sanchez,a   Linfeng Liu,b  Jin-Wook Lee,c   Elena Mas-Marza,a   Hongwei Han,b  Nam-Gyu Park,c   Ivan Mora-Seroa and   Juan Bisquert*ad  
Energy Environ. Sci., 2015, DOI: 10.1039/C4EE03171G

This work describes the transient phenomena that occur in hybrid CH3NH3PbI3 perovskite by measurement of the decay of a photovoltage. This analysis is important in order to understand the coupled electronic-structural phenomena that take place in the operation of the perovskite solar cell when the external influences of voltage and illumination are modified. The study also aims to reveal fundamental insights about the photovoltaic mechanisms of this unique material. The results of our analysis show a separation of the decay stages into two distinct phenomena. Firstly, there are rapid electronic transients in the ms time scale, which are ordinary response times in all kind of solar cells. The novel behaviour is a slow decay in the long time 10-100 s timescale that shows a power law decay that is common in cooperative relaxations as those occurring in polymers and glassy materials. These effects evidence that the perovskite undergoes slow changes in adaptation to external perturbations, very likely associated to the ferroic behaviour of these perovskites. These finding are important for a general analysis of the perovskite and other ferroic solar cells, as these cells have an important degree of freedom, that is the internal state of polarization, that was absent in previous photovoltaic technologies.








Follow

Get every new post delivered to your Inbox.

Join 75 other followers