No abstract

It is of great importance to investigate the crystallization of organometallic perovskite from solution for enhancing performance of perovskite solar cells. Here, this study develops a facile method for in situ observation of crystallization and growth of the methylammonium lead iodide (MAPbI ) perovskite from microdroplets ejected by an alternating viscous and inertial force jetting method. It is found that there are two crystallization modes when MAPbI grows from the CH NH I (MAI)/PbI /N,N-dimethylformamide (DMF) solution: needle precursors and granular perovskites. Generally, needle Lewis adduct of MAPbI ·DMF tends to nucleate and grow from the solution due to low solubility of PbI . The growth of MAPbI ·DMF depends on both the concentration of MAI and temperature. It tends to form large perovskite domains on substrates at high temperature. The MAPbI ·DMF coverts to nanocrystalline perovskite due to lattice shrinkage when DMF molecules escape from the Lewis adduct. Granular perovskite can also directly nucleate from the solution at high concentration of MAI due to compositional segregation.

Perovskite films are usually fabricated by a solution-processed method due to its low cost and ease of fabrication. The organic solvent plays multiple roles in the growth of perovskites. Here, we investigate the growth of methylammonium lead iodide perovskite and its intermediate phase from microdroplets containing various solvents. The perovskite intermediate phase inclines to grow in the direction of its (020) plane from polar aprotic solvents at low temperature. At high temperature, the growth of perovskites depends on the structure of solvent molecules. The intermediate phase still grows from the solvents with a short chain structure. It tends to form smooth films containing radial domains with dimensions in tens of microns, which consist of nanocrystals due to annealing effects. However, perovskite grains grow directly from the solvents with a ring structure. It tends to form smooth thin films by joining the large hexagonal perovskite crystals together. It provides a guidance to prepare high quality perovskite films for high performance optoelectronic devices.

Perovskite structures of organic and inorganic halides are peculiar structures with many interesting properties. Using their photoelectric effect, the structures have been used in photocells, photoelectric sensors, and light-emitting diodes. In conventional perovskite film crystallization, which is a one-step method, the MAPbI 3 crystals form disordered needlelike crystals at room temperature. Such needlelike crystal films have rough surfaces and low coverage to the substrate, resulting in insignificant photoelectric effects. With the assistance of an electric field and three-dimensional (3D) printing, the direction of the perovskite needlelike crystal can be arranged to make it orderly. In this way, the photoelectric sensor of the ordered MAPbI 3 perovskite needlelike crystal film can be prepared. This sensor has high sensitivity, high stability, and high response speed. Moreover, it has anisotropy and higher photoelectric sensitivity in the direction perpendicular to the needle crystal. Most interestingly, the sensors respond differently to polarized light in different directions, and this effect can be used to detect the direction and degree of polarization of polarized light.