A-site composition tuning in methylammonium-based metal halide perovskite colloidal nanocrystals.

Utilizing the soft-lattice nature of metal halide perovskites, we employ post-synthetic cross-ion exchange to synthesize a series of narrow band-gap colloidal nanocrystals of methylammonium-based lead iodide solid solutions of composition FAxMA1-xPbI3, as well as those of triple-cation composition CsxFAyMA1-x-yPbI3 (TCPbI3). The ability to finely tune the compositions not only helps in tailoring the optical properties in the near-infrared region, but also improves the stability of these colloidal nanocrystals towards moisture, which has been demonstrated as compared to their bulk counterparts. The thermal stability of these solid solutions is also comparable to that of the bulk, as evidenced by thermogravimetric studies. This study helps in expanding the composition space of stable 3D lead halide perovskites with band gaps suitable and relevant for photovoltaic applications.