Reversible Halide Exchange Reaction of Organometal Trihalide Perovskite Colloidal Nanocrystals for Full-Range Band Gap Tuning

Abstract

In recent years, methylammonium lead halide (MAPbX3, where X = Cl, Br, and I) perovskites have attracted tremendous interest caused by their outstanding photovoltaic performance. Mixed halides have been frequently used as the active layer of solar cells, as a result of their superior physical properties as compared to those of traditionally used pure iodide. Herein, we report a remarkable finding of reversible halide-exchange reactions of MAPbX3, which facilitates the synthesis of a series of mixed halide perovskites. We synthesized MAPbBr3 plate-type nanocrystals (NCs) as a starting material by a novel solution reaction using octylamine as the capping ligand. The synthesis of MAPbBr(3-x)Clx and MAPbBr(3-x)Ix NCs was achieved by the halide exchange reaction of MAPbBr3 with MACl and MAI, respectively, in an isopropyl alcohol solution, demonstrating full-range band gap tuning over a wide range (1.6-3 eV). Moreover, photodetectors were fabricated using these composition-tuned NCs; a strong correlation was observed between the photocurrent and photoluminescence decay time. Among the two mixed halide perovskite series, those with I-rich composition (x = 2), where a sole tetragonal phase exists without the incorporation of a cubic phase, exhibited the highest photoconversion efficiency. To understand the composition-dependent photoconversion efficiency, first-principles density-functional theory calculations were carried out, which predicted many plausible configurations for cubic and tetragonal phase mixed halides.

Colloidal lead halide perovskite nanocrystals: synthesis, optical properties and applications

“…Such anion exchange was also reported for hybrid MAPbBr 3 NCs, which were synthesized in an approach similar to that of Pérez-Prieto and colleagues, 30 and subsequently mixed with methyl ammonium halide (Cl or I) to produce MAPbBr 3 − x Cl x or MAPbBr 3 − x I x NCs (Figure 5c). 70 The UV-visible absorption and PL emission of both colloidal solutions and films confirmed the composition control of the exchange reaction, demonstrating band gap tuning over the whole visible range (Figure 5d). The anion exchange is also possible in the solid phase as demonstrated by Yang and colleagues.…”

Metal halide perovskites for energy applications

“…The short-term stabilisation of the CsPbI3 NCs in the cubic phase is very interesting, but requires further modification to deliver entirely structurally stable NCs. Notably, a similar strategy has been adopted for the synthesis of MAPbX3 NCs 4,5 and MAPbX3 nanorod arrays 6 (Fig. 1d).…”

Photodetectors Based on Organic–Inorganic Hybrid Lead Halide Perovskites

“…Special micromorphologies such as 2D nanoplates, 1D NWs, 0D nanocrystals, nanonets, and inverse opals‐type structures have been carefully studied and showed superior optical properties and excellent electrical characteristics 52, 53, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65. These structures will be discussed in detail in the following sections.…”