Energy Focus Cite This: ACS Energy Lett. 2019, 4, 879−887 http://pubs.acs.org/journal/aelccp Perovskite Stories from Around the World he surge of interest in perovskite photovoltaics ■ Matt Beard, National Renewable Energy (PVs) in recent years has led to multifaceted research Laboratory, Golden, Colorado, USA; matt.beard@ opportunities. Although metal halide perovskites were nrel.gov; @mbthz Tfi rst discovered more than a century ago, their electronic and light-emitting properties became known only in the 1990s, notably through the work of researchers at IBM T. J. Watson Research Center. It was not until 10 years ago that the first paper on photoelectrochemical investigation of methylammonium lead halide was published. The solid-state PV devices reported in 2012 drew the attention of researchers who were active in the area of dye-sensitized solar cells, organic solar cells, and quantum dot solar cells. This led to the first wave of perovskite photovoltaic research, which mainly focused on boosting the efficiency of solar cells and addressing the issues related to reproducibility and stability. This upsurge was quickly followed by a second wave consisting of researchers who explored the synthesis of new perovskite materials, excited state dynamics, theoretical understanding of the mobility of charge carriers, and Matt Beard and Ye Yang at NREL (photo credit: Dennis Schroeder) defect-driven processes. Researchers around the world are now We were challenged to investigate the optical properties and riding the third wave of perovskites. spectroscopy of perovskite films and crystals by Joey Luther and ACS Energy Letters asked a few of our authors to share their Kai Zhu. At first, we were skeptical that we could add something motivations for pursuing perovskite research. Their quotes useful but decided to study hot-carrier effects. Early on in our (shown alphabetically, below) show their exciting and investigation, Art Nozik (hot-carrier extraordinaire) walked by a interesting experiences during initial days and how they led to computer where one of our carrier-cooling plots was displayed “ ’ ’ success. and exclaimed, that s the best behaved hot-carrier absorber I ve seen”. That is when we realized that maybe there was something to all of the hype about perovskite’s fantastic properties. ■ Osman Bakr, King Abdullah University of Science and Technology (KAUST), Thuwal 23955-6900, ■ Juan Bisquert, Universitat Jaume I, Institute of Saudi Arabia; [email protected] Advanced Materials, Castello, Spain; bisquert@ uji.es Downloaded via UNIV DEGLI STUDI DI PERUGIA on March 22, 2019 at 14:12:20 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. Nam-Gyu Park, Hui-Seon Kim, and Juan Bisquert in Korea, 2013 fi One of the most striking aspects of working with ABX The rst person who spoke to me about the power of hybrid 3 perovskites for photovoltaic applications was Tom Miyasaka. hybrid perovskites is their surprisingly intuitive chemistry, We were duly waiting for our planes in the airport in 2007 after which has made working with them exciting and satisfying. he had just presented the new perovskite-sensitized “quantum ’ Many of our students discoveries on crystallization and dot” solar cell in a conference in Saint Gallen. I was not very compositional tuning of these materials were a result of “Friday impressed but should have paid more attention. The next time I night”-type experiments. However, the field has reached a stage heard about it was in 2012 at some Conference in Asia, and it where a new kind of intuition is required for the metal (B) site was Seigo Ito who mentioned something about a new solar cell one different from those developed in the early days for the organic cation (A) and halide (X) sitesin order to Received: March 7, 2019 achieve breakthrough progress with lead-free perovskite Accepted: March 7, 2019 compositions. © XXXX American Chemical Society 879 DOI: 10.1021/acsenergylett.9b00512 ACS Energy Lett. 2019, 4, 879−887 ACS Energy Letters Energy Focus involving Henry Snaith. He was clearly communicating a sense tried in late September, 2012, Ray made a 3.2% TiO2/ ’ of importance and urgency. I remember well Seigo sglanceand CH3NH3PbI3/CuSCN/Au device, nearly besting my personal fi emphasis, like a calmed auctioneer, suggesting the big value of the record Sb2S3 device on his rst try! When we measured the product with a contained smile, and everyone around taking about devices for 10 min at short-circuit, we saw an approximately 50% it very seriously, making metal notes, and requesting more decrease in photocurrent and a visible bleaching of the information. Soon Nam-Gyu Park emerged as one of the leaders of perovskite layer. This led us to switch from CuSCN to CuI, the new field, and his student Hui-Seon Kim came in late 2012 to which initially had lower efficiencies of only about 2% but were Castellóforsometimetoanalyzeoperationofthedevice. much more stable. We struggled greatly just reproducing our I remember Michael Gratzel̈ presenting 14% efficiency at HOPV own results because we did not understand the effects of Conference in Seville in May 2013. Clearly a race was starting and atmospheric humidity at all in these early days. After working a a lot of surprises lay ahead. Now in 2019, we still expect a few more. few more months on the project, I had made a 6% efficient fi TiO2/CH3NH3PbI3/CuI/Au, device and we had the rst ■ David Cahen, Weizmann Institute of Science and perovskite paper with all inorganic contacts; it was still measured Bar-Ilan University, Israel; [email protected] over 4% efficient after discovering it in the back of my drawer 1 year later! ■ Songyuan Dai, North China Electric Power University, Beijing 102206, P. R. China; sydai@ ncepu.edu.cn Rump Session for Organo-Metal Halide Perovskite-Based Solar Cells. 2013 MRS Fall Meeting, Boston, ©Materials Research Society (Reprinted with permission) It is been called a formative experience. While, as originator of the idea, I’d love this to be so, even if it was not, it likely had some effect. During a meeting in Japan I learned about the then fresh off the press Lee et al. 2012 Science paper. Gary Hodes and I worked at that time to find not GaAs but GaInP on the cheap; Perovskite solar cells appeared as a hot topic at the 7th Aseanian the high voltage efficiency dazzled me, and upon return, we forewent Conference on Nanohybrid Solar Cells 2012 in Taiwan. Prof. Nam-Gyu Park, Prof. Henry Snaith, and Prof. Tom Miyasaka good old (Cd,Zn)(S,Se,Te) for MAPbBr3. During the next year, I tried, not always successfully, to infect colleagues with “perovskitis”, reported their exciting result of hybrid metal halide perovskites, arguing this was a potential game changer. At the same time, the which revealed a new era of solar cell research. I believed that all MRS meetings were frustrating as they missed the change that I felt of the participates were convinced that PSCs would be the next in the air. As MRS board member, I searched during an August 2013 breakthrough in solar cells. What happened afterward fully board meeting to do something about it for the upcoming Fall supported this optimistic expectation. Inspired by the pioneering works, my group published some meeting and called Dave Ginley, former MRS president. I do not fi remember all of the reasons why nothing could be done, but in the subsequent papers on doping modi cation and hole trans- end, we convinced MRS, and the rest is history. porting materials for PSCs soon after. Our current research are aimed at developing two-dimensional perovskites with high ffi ■ Jeff Christians, Hope College, Holland MI, USA; power conversion e ciency and moisture resistance. Through a [email protected]; @jac997 combination of theoretical and experimental approaches, one of our recent works found that the properties of perovskite materials can be modified by adding different ammonium salts into FAPbI3. I have faith that PSCs will pave the way for cheap, stable, and highly efficient solar cell devices. ■ Filippo De Angelis, University of Perugia, and CNR- ISTM, Perugia, Italy; fi[email protected] I remember reading the landmark Scientific Reports paper soon after it appeared online in 2012, and almost immediately Prashant Kamat, my graduate advisor, and I had Raymond Fung, an under- graduate researcher working with us at the time, start working on perovskites. At the time I was making TiO2/Sb2S3/CuSCN/Au Filippo De Angelis (left) and Edoardo Mosconi (right) at the Computational Laboratory for Hybrid/ solarcells;wedidnothavespiro-OMeTADinthelabsowetookthe Organic Photovoltaics in Perugia fi same process/structure I was using for Sb2S3 solar cells and plugged I rst heard about lead-halide perovskites from Henry Snaith at a fi in CH3NH3PbI3.InwhatIbelievewasthe rst batch of devices he European project meeting in June 2012 (I must admit I had 880 DOI: 10.1021/acsenergylett.9b00512 ACS Energy Lett. 2019, 4, 879−887 ACS Energy Letters Energy Focus missed Miyasaka’s 2009 paper), a few weeks after Kanatzidis published the paper on CsSnI3-based solid-state DSCs. Henry fi ∼ ffi rst showed us MAPbI3/TiO2 solar cells with 6% e ciency, which I considered with some curiosity. That was, however, just ∼ ffi thepreambletoshowingusa 10% e cient MAPbI3/Al2O3 solar cell. This result left the small audience astonished, testifying the semiconducting nature of lead-halide perovskites and paving the way to a new type of device. Later that day, I called my wife (Simona Fantacci, a colleague also working in modeling DSCs), telling her that I had witnessed a scientific breakthrough. I started working on perovskites at CNR-ISTM, Perugia during the summer of 2012 with co-workers Anna Amat and fi ̈ QD solar cells were presented (that time the thin lm perovskite Edoardo Mosconi.