Engineering Halide Perovskite Crystals through Precursor Chemistry

Abstract

The composition, crystallinity, morphology, and trap‐state density of halide perovskite thin films critically depend on the nature of the precursor solution. A fundamental understanding of the liquid‐to‐solid transformation mechanism is thus essential to the fabrication of high‐quality thin films of halide perovskite crystals for applications such as high‐performance photovoltaics and is the topic of this Review. The roles of additives on the evolution of coordination complex species in the precursor solutions and the resulting effect on perovskite crystallization are presented. The influence of colloid characteristics, DMF/DMSO‐free solutions and the degradation of precursor solutions on the formation of perovskite crystals are also discussed. Finally, the general formation mechanism of perovskite thin films from precursor solutions is summarized and some questions for further research are provided.

Origin of High Efficiency and Long-Term Stability in Ionic Liquid Perovskite Photovoltaic

“…A strong Pb-O coordination peak was observed at near 1.65 Å in the MAAc precursor solution, and a small amount of Pb-I coordination is present at near 2.6 Å. In contrast, DMF precursor solution exhibited a strong Pb-I coordination peak with a small amount of Pb-O coordination, which indicates that the perovskite precursor in the DMF solvent is dominated by iodine complexes due to the greater coordination capacity of I − than DMF, as in previous reports [ 29 , 30 ]. Moreover, as shown in Figure 2(f) , the 1 H NMR spectra of the three perovskite precursor solutions (MAPbI 3 , FAPbI 3 , and CsPbI 3 ) showed the clear blue shift of the N-H peak with respect to the pure MAAc solvent (shown in an internal enlarged view in Figure 2(f) ), which proved the formation of hydrogen bonding of N-H⋯I between MAAc and PbI 2 and/or MAI (CsI).…”

Shining Light on the Photoluminescence Properties of Metal Halide Perovskites

“…In fact, there are so many reports of additives that it might be more productive to ask what materials have not been mixed with perovskites. This topic has been reviewed extensively by Li et al [ 265 ] and Li et al [ 189 ] where they have discussed polymers, solvents, fullerenes, nanoparticles, metal or organic halide salts, inorganic acids, and more, with a range of benefits including enhanced crystallization kinetics for more uniform grains and defect passivation. As this list of potential additives is too exhaustive to be covered here, we instead will present a series of experiments which utilized PL measurement techniques as a powerful tool to understand the additives' effect on the perovskite photophysics.…”

New Synthetic Route of Ultrapure Alkylammonium Iodides for Perovskite Thin Films of Superior Optoelectronic Properties

“…We can link the amount of phosphorus‐based impurities in the MAI powder to the size of colloidal species present in the perovskite precursor solution, which is consistent with the observations made by Levchuk et al [ 14 ] It was proposed in multiple reports that colloids present in the perovskite precursor solutions are based on lead polyhalide coordination networks. [ 15,25 ] These species can substantially affect the nucleation and crystallization rates of perovskite layer. McMeekin et al proposed that they could act as heterogeneous nucleation centers.…”

“…Similarly, other additives and impurities (acids, amines, organic halides, and water additive) can affect the colloidal chemistry occurring in the perovskite precursor solution, which in turn would have an impact on the nucleation process and perovskite thin‐film morphology. [ 10,15,16 ] As an alternative to one‐step, solution‐based processing, multiple variations of a two‐step fabrication route of metal halide perovskite films were reported. [ 17,18 ] Particularly, gas‐induced growth method, where lead iodide films are exposed to alkylamine vapor, constitutes a deposition strategy which eliminates the problem of poorly controlled purity of alkylammonium salts.…”