Viewpoint pubs.acs.org/JPCL
Cite This: J. Phys. Chem. Lett. 2017, 8, 5688-5688
In the Limelight: Perspective Collections on Perovskites n our last “In the Limelight” article, we introduced Perspective Collections, which The Journal of Physical Chemistry Letters will begin publishing in 2018. Each of our new Perspective Collections has a central focus on a topic of emerging interest in physical chemistry research and is organized by an area expert. The organizing editor chooses the topic and the authors, who are invited based on their specific areas of expertise and unique viewpoints. This is the second in a series of “In the Limelight” Viewpoint articles that will introduce these collections and their organizers. Thomas Kirchartz (Forschungszentrum Jülich) is organizing a collection on the topic “Optics and Photon Management in Metal-Halide Perovskites for Optoelectronic Applications.” As stated in the full topic description, “It is obvious that the optical properties of metal-halide perovskites and the broad topic of photon management are generally crucial for optoelectronic devices. However, the initial focus of research was mostly on electronic and interfacial properties as well as questions of processing and device architecture. Recently, there has been an increasing interest in topics that focus more on the optical properties or look at the interaction between the optics of the device and the electronic properties that one would measure.” Kirchartz recently coauthored “Decreasing Radiative Recombination Coefficients via an Indirect Band Gap in Lead Halide Perovskites” with Uwe Rau (J. Phys. Chem. Lett., 2017, 8, 1265−1271, DOI: 10.1021/acs.jpclett.7b00236; accessed online 775 times as of November 7, 2017). Kirchartz became interested in the topic when he read two articles that found physical evidence for an indirect band gap energetically close to the direct band gap in methylammonium lead iodide. The articles suggested that this indirect band gap may have something to do with the remarkably long charge carrier lifetimes in this material. “This topic is a very fundamental one for photovoltaics,” said Kirchartz. “Essentially it is based around the question of whether it is possible to sacrifice one thing to enhance something else. In this case, the material would sacrifice absorption strength around the band gap for longer chargecarrier lifetimes. If this was working, indirect semiconductors would be the materials to look for when attempting to identify new and promising solar cell absorber materials.” Because this idea contradicted conventional wisdom, Kirchartz and Rau decided that it was worth exploring. They concluded that, although it is in principle possible to increase the radiative lifetime by sacrificing absorption or energy, the property of methylammonium lead iodide that makes it attractive for optoelectronics is not a slow radiative lifetime but instead a slow nonradiative lifetime and therefore a high luminescence efficiency. “We did not find a reason to explain this feature with an indirect band gap,” said Kirchartz, “thus, we remain skeptical whether MAPI has such remarkable properties because of or rather despite the slightly indirect band gap.” Kaibo Zheng and Tönu Pullerits (Lund University) are organizing a collection on the topic “Are Two Dimensions
I
© 2017 American Chemical Society
Better for Perovskites?” As they note in the full description, “Organic−inorganic halide perovskites have emerged as highly promising family of optoelectronics materials. The recent development of 2-dimensional Ruddlesden−Popper-type structures of these materials has shown promise to solve one of the main problems with the perovskitesthe stability issues.” Zheng and Pullerits recently coauthored “Direct Experimental Evidence for Photoinduced Strong-Coupling Polarons in Organolead Halide Perovskite Nanoparticles” with Mohamed Abdellah, Qiushi Zhu, Qingyu Kong, Guy Jennings, Charles A. Kurtz, Maria E. Messing, Yuran Niu, David J. Gosztola, Mohammed J. Al-Marri, Xiaoyi Zhang, and Sophie E. Canton (J. Phys. Chem. Lett., 2016, 7, 4535−4539, DOI: 10.1021/acs.jpclett.6b02046; accessed online 688 times as of November 7, 2017). It is one of a series of articles that Zheng and Pullerits have published on the nanoparticles of organolead halide perovskite material, and the first where optical pump−Xray probe time-resolved spectroscopy was used on the perovskite. “The nanoparticles are well suited for such study since one can flow the sample to avoid photodamage,” said Pullerits. He adds that perovskite material is prone to defects, which would normally lead to poor device performance. “Apparently, in some way, the perovskite material does not care,” said Pullerits. “The efficiency of the solar cells is very high. We hope that our work provides some important hints how and why this material works so well. It is good if something works, but we’d better understand why it works. If we understand, we should be able to make it even better.”
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
■
Northwestern University
AUTHOR INFORMATION
ORCID
Gregory D. Scholes: 0000-0003-3336-7960 Notes
The authors declare no competing financial interest. Published: November 16, 2017 5688
DOI: 10.1021/acs.jpclett.7b02970 J. Phys. Chem. Lett. 2017, 8, 5688−5688
