Mixed-halide perovskite synthesis by chemical reaction and crystal nucleation under an optical potential

Abstract

The development of new methods to engineer lead halide perovskite crystals with a controlled band gap and emission properties is an active subject in materials science and chemistry. We present the preparation of mixed-halide lead perovskites by spatially- and temporally- controlled chemical reactions and crystal growth under an optical potential in unsaturated precursor solutions. The crystals are characterized by transmission and photoluminescence spectral measurements and X-ray diffraction analysis. When compared with the spontaneous formation of multiple crystals in saturated precursor solutions, the optical potential creates large single crystals with a high chloride composition, providing distinct blue and green fluorescent crystals of chloride–bromide lead perovskites. We discuss the formation of mixed-halide perovskites from the viewpoints of an increased rate of chemical reaction via the formation and desolvation of precursor complexes and a decreased free energy potential.

Optical materials: laser trapping for halogen mixed perovskite single-crystal synthesis

A technique that uses lasers to control chemical reactions has been shown by researchers in Japan to modify the optical properties of photovoltaic materials. Lead halide perovskites have emerged recently as an exciting option for optoelectronic applications, particularly solar cells. This technology requires a method that can produce large-area samples with high crystalline quality. Ken-ichi Yuyama, Vasudevanpillai Biju, and their colleagues from Hokkaido University, focused laser light in a precursor solution, which increased the concentration of molecules and initiated chemical reaction and crystal growth. This precise chemical control enabled the synthesis of highly luminescent chloride–bromide lead perovskite single crystals with a higher chloride composition than is possible using spontaneous crystal formation. The extra chloride shifted the optical fluorescence of the material into the blue part of the spectrum.