Persistent Dopants and Phase Segregation in Organolead Mixed-Halide Perovskites

Abstract

O r g a n o l e a d m i x e d -h a l i d e p e r o v s k i t e s s u c h a s CH 3 NH 3 PbX 3−a X′ a (X, X′ = I, Br, Cl) are interesting semiconductors because of their low cost, high photovoltaic power conversion efficiencies, enhanced moisture stability, and band gap tunability. Using a combination of optical absorption spectroscopy, powder X-ray diffraction (XRD), and, for the first time, 207 Pb solid state nuclear magnetic resonance (ssNMR), we probe the extent of alloying and phase segregation in these materials. Because 207 Pb ssNMR chemical shifts are highly sensitive to local coordination and electronic structure, and vary linearly with halogen electronegativity and band gap, this technique can provide the true chemical speciation and composition of organolead mixed-halide perovskites. We specifically investigate samples made by three different preparative methods: solution phase synthesis, thermal annealing, and solid phase synthesis. 207 Pb ssNMR reveals that nonstoichiometric dopants and semicrystalline phases are prevalent in samples made by solution phase synthesis. We show that these nanodomains are persistent after thermal annealing up to 200 °C. Further, a novel solid phase synthesis that starts from the parent, single-halide perovskites can suppress phase segregation but not the formation of dopants. Our observations are consistent with the presence of miscibility gaps and spontaneous spinodal decomposition of the mixed-halide perovskites at room temperature. This underscores how strongly different synthetic procedures impact the nanostructuring and composition of organolead halide perovskites. Better optoelectronic properties and improved device stability and performance may be achieved through careful manipulation of the different phases and nanodomains present in these materials.

Lead and iodide deficient (CH3NH3)PbI3, d-MAPI: the bridge between 2D and 3D hybrid perovskites

“…[28] All studied samples of d-MAPI show essentially the same signal, with the intensities being reduced for the d-MAPI samples,a nd no additional signals could be found (Supporting Information, Figure S17). [28] All studied samples of d-MAPI show essentially the same signal, with the intensities being reduced for the d-MAPI samples,a nd no additional signals could be found (Supporting Information, Figure S17).…”

“…Zuschriften mobility despite its bigger size.The Pb 2+ cations of MAPI can also be investigated by 207 Pb NMR, yielding an unstructured broad signal owing to fast transverse relaxation. [28] All studied samples of d-MAPI show essentially the same signal, with the intensities being reduced for the d-MAPI samples,a nd no additional signals could be found (Supporting Information, Figure S17).…”

The Relation of Phase‐Transition Effects and Thermal Stability of Planar Perovskite Solar Cells

“…[1,2] Although a certified η of 22.1% has been achieved through state-ofthe-art device engineering, the device stability is still not sufficient for widespread commercialization. [1,2] Although a certified η of 22.1% has been achieved through state-ofthe-art device engineering, the device stability is still not sufficient for widespread commercialization.…”

Lead‐ and Iodide‐Deficient (CH3NH3)PbI3 (d‐MAPI): The Bridge between 2D and 3D Hybrid Perovskites

“…Thus, also the HEA + exhibits a high mobility despite its bigger size. The Pb 2+ cations of MAPI can also be investigated by 207 Pb NMR, yielding an unstructured broad signal owing to fast transverse relaxation . All studied samples of d ‐MAPI show essentially the same signal, with the intensities being reduced for the d ‐MAPI samples, and no additional signals could be found (Supporting Information, Figure S17).…”