Abstract
Chlorine incorporation engineering has been widely used in optoelectronic devices based on methylammonium lead iodide (MAPbI3) perovskites. However, the characteristics of I/Cl alloying structures in MAPbI3−xClx mixed-halide perovskites and their influences on the optoelectronic properties have been issues of a long-standing controversy. Here, we present a detailed study of the I/Cl alloying structures in MAPbI3−xClx (x = 0.0 to 0.3) single crystals. We found that a small amount of Cl can substitute for the iodide of the PbI3 inorganic lattice, leading to a phase transition from the tetragonal to cubic phase and anomalous cation dynamics evolution. Analyses based on time-dependent X-ray diffraction, 207Pb NMR, and 2H NMR indicate that the alloying structures of the MAPbI3−xClx crystals are metastable and decompose over time. In addition, the photocurrent response measurement of MAPbI3−xClx proved a close correlation between the alloying structures and photoelectric properties of the material. This work sheds light on the essential understanding of the I/Cl alloying structure and provides a plausible explanation for the controversy regarding the role of chloride ions in optoelectronic devices.
Highlights
The development of organic-metal halide perovskite materials with the formula ABX3, where A is generally either methylammonium (MA) or formamidinium (FA), B is Pb or Sn, and X is I, Br, or Cl, has rapidly progressed in recent years
This long-term instability indicates that different conclusions regarding the effect of Cl ions on the properties of MAPbI3−xClx perovskites may arise over different time scales, which provides a plausible explanation for the long-standing controversy regarding the effect of Cl ions on the performance of optoelectronic devices based on MAPbI3−xClx
The optoelectronic properties of the MAPbI3−xClx single crystals deteriorate over time. This long-term instability indicates that different conclusions regarding the effect of Cl ions on the optoelectronic properties of MAPbI3−xClx perovskites may arise over different time scales, which provides a plausible explanation for the long-standing controversy regarding the effect of Cl ions on the performance of optoelectronic devices based on MAPbI3−xClx
Summary
The development of organic-metal halide perovskite materials with the formula ABX3, where A is generally either methylammonium (MA) or formamidinium (FA), B is Pb or Sn, and X is I, Br, or Cl, has rapidly progressed in recent years These materials have been employed in a wide array of applications, such as in solar cells[1,2,3], photodetectors[4], light-emitting diodes (LEDs)[5], transistors[6], and lasers[7], owing to their excellent optoelectronic performances, such as adjustable bandgaps[8], high absorption coefficients[9], and long charge-carrier diffusion lengths[10]. On one side of the above-discussed debate, many reports have provided evidence indicating that no Cl ions are embedded in the inorganic PbI3 lattice. Zhang et al.[23] reported that Cl can be maximally doped into the
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