Nanostructured Energy Devices
There is an enormous variety of exotic properties in the methylammounium triiodideplumbate perovskite and related photovoltaic perovskites. A range of important questions are being discussed in meetings and papers. If there is consensus about one point among the main theorists of the field, it is that it is extremely unlikely that excitons persist for any significant time, due to dielectric screening. This view has been clearly expressed in the following papers
Frost, J. M.; Butler, K. T.; Brivio, F.; Hendon, C. H.; van Schilfgaarde, M.; Walsh, A. “Atomistic Origins of High-Performance in Hybrid Halide Perovskite Solar Cells”. Nano Letters 2014, 14, 2584-2590. (They state: It is clear that excitons will not play a significant role in the photovoltaic device physics.)
Menendez-Proupin, E.; Palacios, P.; Wahnon, P.; Conesa, J. C. “Self-consistent relativistic band structure of the CH3NH3PbI3 perovskite”. Physical Review B 2014, 90, 045207.
Analysis of Multivalley and Multibandgap Absorption and Enhancement of Free Carriers Related to Exciton Screening in Hybrid Perovskites, Jacky Even, Laurent Pedesseau, and Claudine Katan, 2014, 118 (22), pp 11566–11572 (” Our analysis suggests exciton screening by collective orientational motion of the organic cations at room temperature, leading to almost free carriers.”)
For experimental results see
Two nanoGe Conferences celebrated in Oxford last week showed the extraordinary strength of the development of perovskite solar cells and the great general interest of quantum dots fundamental physics and solar cells.
The Conference on Solution processed semiconductor solar cells, being celebrated in Henry Snaith’s place, obtained massive fluence from perovskite solar cells people. Many presentations and discussions showed that the questions are being centered about relevant properties of the perovskite solar cell. After some period of puzzlement by the extraordinary novel characteristics, now everybody starts to present the questions and comes up with original explanations, that undoubtedly will be addressed in the the next months in the literature and in discussion forums. It is a nice generating moment in this field. The very fast development of materials was highlighted for example by Yang Yang presentation of the noted Science paper with efficiency over 19%. New interesting applications were suggested by Miyasaka exploiting the ferroic properties of the perovskite. Emilio Palomares came up with a happy metaphor about the current interest of the perovskite for new researchers with respect to the previous families of hybrid solar cells. The presence of quantum dot solar cells was less than in previous years but still showed innovative results especially about doping of nanocrystalas and formation of heterostructures. These questions as well as ultarfast phenomena and new applications (bio, LEDs) were also discussed in the conference on fundamentals by an impressive list of speakers and participants.
Both conferences benefited from the presence of Prof. Rudolph Marcus, Nobel laureate, that was very interested in the electron transfer problems and in the perovskite solar cells. It was wonderful and inspiring to talk to the great master.
Speakers and organizers SSSC14. Row 1: Tsutomu Miyasaka, Gary Hodes, Rudolph Marcus, Henry Snaith, Lioz Etgar, Arthur Nozik. Row 2: Seigo Ito, Nam-Gyu Park, David Mitzi, Alex Jen, Feliciano Giustino, Sam Stranks. Row 3: Satoshi Uchida, Iván Mora-Seró, Juan Bisquert, Emilio Palomares, Mercouri Kanatzidis, Arie Zaban.
Rudolph Marcus and JB
Group photo FQDots14. Speakers and organizers Row 1: Sandy Ruhman, Zeger Hens , Laurens Siebbeles, Liberato Manna, Patanjali Kambhampati, Arthur Nozik, Daniël Vanmaekelbergh, Tom Gregorkiewicz, Rudolph Marcus, Efrat Lifshitz, Jonathan Owen, Dmitri Talapin. Row 2: Alf Mews , Christian Klinke, Arjan Houtepen, Ulrike Woggon, Todd Krauss, David Norris, Others: Horst Weller, Uri Banin, Alexander Eychmuller.
Efrat Lifshitz and Laurens Siebbels, chairs
nanoGe staff Laura, Ramona, Paloma and friend Mario
Nam Gyu Park, JB and Emilio Palomares (insisting he is a doctor)
A comparison of evolution of solar cells and phone cells according to Emilio.
Staggering increases in the performance of organic–inorganic perovskite solar cells have renewed the interest in these materials. However, further developments and the support from academic and industrial partners will hinge on the reporting of accurate efficiency values.
As pointed out by Grätzel, some open issues and pitfalls are now being debated in this community. Among these, the main concern revolves around the accuracy of the reported efficiency values. Specifically, hysteretic behaviour due to the strong dependence of the photocurrent on the voltage-scan conditions seems to be particularly pronounced in some perovskite solar cells. This has led to doubts about some reported power-conversion efficiency values, which may be altered by hysteresis-related artefacts.
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