Viewpoint pubs.acs.org/JPCL
In the Limelight n our inaugural “In the Limelight” Viewpoint, we revisited five high-impact papers that were published in The Journal of Physical Chemistry Letters (JPC Letters) in 2014, and we noted that four of the five were written on the topic of perovskites. Three years later, we can see that this was not an anomaly: Perovskites continue to be an active research topic and interest readers of the journal and authors alike. The word “perovskite” first appeared in a JPC Letters title in the journal’s third issue, but more than 2 years would pass until the next title appearance. As perovskites have moved into the forefront of physical chemistry research, the journal has led the way, publishing around 90 articles with “perovskite” in the title in each of the last 2 years. Here we will discuss two such papers that have attracted notice. Ivan Kassal and Samantha N. Hood’s article “Entropy and Disorder Enable Charge Separation in Organic Solar Cells” (J. Phys. Chem. Lett. 2016, 7, 4495−4500. DOI: 10.1021/acs.jpclett.6b02178) was published late last year and has already been accessed online more than 570 times and cited in seven articles (source of citation data: Web of Science, Clarivate Analytics, accessed August 4, 2017). Kassal became interested in the subject of the article after studying light harvesting in photosynthesis. “I realized that much of the same physics is present in organic solar cells, so maybe I could have something interesting to say,” said Kassal. “When I came to the field, all the reviews said that a major puzzle was how the bound electron and the hole overcome their seemingly huge Coulomb interaction to become free carriers that can contribute to electrical current. Charge separation is perhaps the most elementary process in organic solar cells, and I was intrigued that it was apparently still unexplained. This paper rose out of something all chemists learn in first year: it is the free energy, not just the energy, that determines which processes can happen simultaneously.” The authors knew that theirs was a simple argument, so they made the writing as accessible as possible. As a result, says Kassal, some of his colleagues have used the article in their undergraduate chemistry classes. The authors’ work is part of the explosive growth of research in the area of clean energy generation to combat climate change, and Kassal notes that there is still work to be done. “Organic solar cells are particularly promising because they promise energy that is cheaper, flexible, solution-processable, and more tunable using chemical techniques,” said Kassal. “We are theorists working on unraveling the basic processes that allow organic solar cells to function, with the goal of providing principles for designing better devices.” Another article that is having an impact comes from the same issue. “Bright Perovskite Nanocrystal Films for Efficient LightEmitting Devices” by Xiaoyu Zhang et al. (J. Phys. Chem. Lett. 2016, 7, 4602−4610. DOI: 10.1021/acs.jpclett.6b02073) has been accessed online more than 1300 times and cited in 10 articles (source of citation data: Web of Science, Clarivate Analytics, accessed August 4, 2017). Corresponding author Yu Zhang notes that lighting is part of our daily lives. “We are the guys who aim to cut off energy consumption and enhance the
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© 2017 American Chemical Society
color-rendering index of light-emitting diodes (LEDs).” Because of the high demand for LEDs, it is crucial for researchers to find emitter materials that are cheaper and easier to preparewithout sacrificing device performance. “As we mentioned, perovskite quantum dots (QDs) have excellent optical properties that fully meet the requirements for LED emitters,” said Zhang. “The large mobilities in perovskites are promising for LEDs that can achieve high brightness at low driving voltages. Besides, the perovskite QDs are low cost and can be synthesized easily via a room-temperature procedure, which fully meets the requirement for future solutionprocessed, flexible, and large-area device applications. Perovskite QDs are promising materials for LEDs of both optical quality and low cost, and our prototype devices initially proved this feasibility.” Zhang notes that organic LED (OLED) screens have become ubiquitous, and some believe that QD LEDs will replace them because of their higher-emission color purity. “Perovskite QDs have narrower emission line widths than traditional CdSe and InP QDs,” said Zhang. “Our red, green, and blue perovskite QD prototype devices have demonstrated the potential of perovskite QD emitters, and there are surely more and more people studying perovskite QD LEDs currently. Along with the development of device physics and material chemistry, we are full of confidence for the practical application of perovskite QD LEDs.”
Gregory D. Scholes Princeton University
Juan Bisquert Universitat Jaume I
Maria Forsyth Deakin University
Benedetta Mennucci University of Pisa
Oleg Prezhdo University of Southern California
Francisco Zaera University of California, Riverside
Timothy Zwier Purdue University
George C. Schatz
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Northwestern University
AUTHOR INFORMATION
ORCID
Gregory D. Scholes: 0000-0003-3336-7960 Notes
The authors declare no competing financial interest.
Received: August 7, 2017 Accepted: August 7, 2017 Published: August 17, 2017 3925
DOI: 10.1021/acs.jpclett.7b02071 J. Phys. Chem. Lett. 2017, 8, 3925−3925
