Lead halide perovskites: Challenges and opportunities in advanced synthesis and spectroscopy

Hybrid lead perovskites containing a mixture of organic and inorganic cations and anions have led to solar cell devices with performance and stability that are better than those of their single-halide analogs. 207Pb solidstate nuclear magnetic resonance and single-particle photoluminescence spectroscopies show that the structure and composition of mixed-halide and likely other hybrid lead perovskites are much more complex than previously thought and are highly dependent on their synthesis. While a majority of reports in the area focus on the construction of photovoltaic devices, this Perspective focuses instead on achieving a better understanding of the fundamental chemistry and photophysics of these materials, because this will aid not only in constructing improved devices but also in generating new uses for these unique materials. Disciplines Chemistry Comments This is an article from Rosales, Bryan A., Michael P. Hanrahan, Brett W. Boote, Aaron J. Rossini, Emily A. Smith, and Javier Vela. "Lead halide perovskites: Challenges and opportunities in advanced synthesis and spectroscopy." ACS Energy Letters2, no. 4 (2017): 906-914. doi: 10.1021/acsenergylett.6b00674. Posted with permission. Rights This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes. Authors Bryan A. Rosales, Michael P. Hanrahan, Brett W. Boote, Aaron Rossini, Emily A. Smith, and Javier Vela This article is available at Iowa State University Digital Repository: http://lib.dr.iastate.edu/chem_pubs/994 Lead Halide Perovskites: Challenges and Opportunities in Advanced Synthesis and Spectroscopy Bryan A. Rosales,† Michael P. Hanrahan,†,‡ Brett W. Boote,†,‡ Aaron J. Rossini,*,†,‡ Emily A. Smith,*,†,‡ and Javier Vela*,†,‡ †Department of Chemistry, Iowa State University, Ames, Iowa 50011, United States ‡US DOE Ames Laboratory, Ames, Iowa 50011, United States *S Supporting Information ABSTRACT: Hybrid lead perovskites containing a mixture of organic and inorganic cations and anions have led to solar cell devices with performance and stability that are better than those of their single-halide analogs. Pb solid-state nuclear magnetic resonance and single-particle photoluminescence spectroscopies show that the structure and composition of mixed-halide and likely other hybrid lead perovskites are much more complex than previously thought and are highly dependent on their synthesis. While a majority of reports in the area focus on the construction of photovoltaic devices, this Perspective focuses instead on achieving a better understanding of the fundamental chemistry and photophysics of these materials, because this will aid not only in constructing improved devices but also in generating new uses for these unique materials. Hybrid lead perovskites containing a mixture of organic and inorganic cations and anions have led to solar cell devices with performance and stability that are better than those of their single-halide analogs. Pb solid-state nuclear magnetic resonance and single-particle photoluminescence spectroscopies show that the structure and composition of mixed-halide and likely other hybrid lead perovskites are much more complex than previously thought and are highly dependent on their synthesis. While a majority of reports in the area focus on the construction of photovoltaic devices, this Perspective focuses instead on achieving a better understanding of the fundamental chemistry and photophysics of these materials, because this will aid not only in constructing improved devices but also in generating new uses for these unique materials. Lead halide perovskites with the general formula APbX3, where A is an organic (CH3NH3, CH(NH2)2) or inorganic cation (Cs) and X is a halide (I−, Br−, or Cl−), have gained much attention as photovoltaic materials because of their high power conversion efficiency (PCE) of over 22%. These semiconducting materials exhibit many useful and interesting properties, including low cost and ease of synthesis (to an extent; see below), and have large absorption coefficients, intense photoluminescence, low exciton binding energies, long exciton diffusion lengths, high dielectric constants, and intrinsic ferroelectric polarization. In addition, the perovskite structure is highly tunable because of the variety of organic and inorganic cations (A), central elements (in lieu of Pb), and anions (X) that can be incorporated into a variety of “hybrid” structures, resulting in complete optical tunability over the entire visible spectrum. In this Perspective, we highlight our team’s efforts in the spectroscopic-driven synthetic development of hybrid mixedhalide lead perovskites. Pb solid-state nuclear magnetic resonance (ssNMR) spectroscopy has allowed us to test the true chemical speciation of the lead nucleus, and optical spectroscopy has allowed us to correlate nanocrystal morphology and composition with single-particle luminescence. Hybrid mixed-halide perovskites and their devices display improved stability and performance in comparison to their single-halide analogs, and our results show that their structure and composition are much more complex than previously thought and are highly dependent on their synthesis. By providing a more detailed understanding of their fundamental chemistry and photophysics, further synthetic and advanced ssNMR, photoluminescence, and Raman spectroscopic experiments will help unlock the full potential of hybrid lead perovskites and related materials in solar cells and beyond. Synthetic Development: Toward Structure−Property Relationships for Enhanced Stability and Performance. Lead halide perovskites are typically synthesized by spin-coating, vapor deposition, or precipitation from solution. Figure 1 illustrates these methods using methylammonium-based organolead halide perovskites, CH3NH3PbX3 (X = I, Br, Cl), as an Received: December 9, 2016 Accepted: March 3, 2017 Published: March 3, 2017 Pb solid-state nuclear magnetic resonance (ssNMR) spectroscopy has allowed us to test the true chemical speciation of the lead nucleus, and optical spectroscopy has allowed us to correlate nanocrystal morphology and composition with single-particle luminescence. Pespec iv e http://pubs.acs.org/journal/aelccp © 2017 American Chemical Society 906 DOI: 10.1021/acsenergylett.6b00674 ACS Energy Lett. 2017, 2, 906−914 This is an open access article published under an ACS AuthorChoice License, which permits copying and redistribution of the article or any adaptations for non-commercial purposes.