Single Crystal Growth of Hybrid Lead Bromide Perovskites Using a Spin-Coating Method

R. García-Aboal; R. Fenollosa; F. Ramiro-Manzano; I. Rodríguez; F. Meseguer; P. Atienzar

doi:10.1021/acsomega.8b00447

Research · Publication & note

Single Crystal Growth of Hybrid Lead Bromide Perovskites Using a Spin-Coating Method

ACS Omega · Journal article · 15 May 2018

R. García-Aboal, R. Fenollosa, F. Ramiro-Manzano, I. Rodríguez, F. Meseguer and P. Atienzar

ACS Omega

Volume 3

Pages 5229-5236

2018

Abstract

Synthesis and studies of single crystals of hybrid perovskite are important for achieving a better understanding of the optoelectronic phenomena occurring in this material and for improving ongoing applications. Here, we report on the growth of micrometer-size single crystals of methylammonium lead bromide (MAPbBr₃) using the spin coating deposition method on a quartz substrate. We studied the influence of the rotation speed and the use of three different additives N-cyclohexyl-2-pyrrolidone, dimethyl sulfoxide, and 4-tert-butylpyridine on the crystal size and shape. The introduction of an additive in the precursor solution is revealed to be very useful for obtaining crystals with well-defined geometries and for decreasing the amount of defects. In this way, high-quality single crystals that sustain optical resonating modes were obtained and characterized by transmittance and photoluminescence measurements.

How to cite

Article access and reuse

This is an open-access article published under the Standard ACS AuthorChoice usage agreement, which permits non-commercial copying, display and redistribution with attribution and a prominent link to the definitive ACS version. The complete embedded figure compositions below were extracted directly from the article PDF without changing their content.

Figures

Figure 1 from the ACS Omega article — **Figure 1.** Average crystal size (dots) as a function of the spin coater rotation speed for a precursor solution without additive (A) and with (B) CHP, (C) DMSO, and (D) TBP as additive. The error bars correspond to the standard deviation. The grey lines are fits to functions proportional to 1/speed^γ.

Figure 2 from the ACS Omega article — **Figure 2.** Scanning electron microscopy (SEM) images of MAPbBr₃ crystals grown on quartz substrates by spin coating at 1000 rpm, corresponding to samples NA (a), CHP (b), DMSO (c), and TBP (d).

Figure 3 from the ACS Omega article — **Figure 3.** XRD pattern of a layer of crystals of (a) NA, (b) CHP, (c) DMSO, and (d) TBP samples.

Figure 4 from the ACS Omega article — **Figure 4.** (a)-(d) Optical microscopy images at 40× magnification of samples NA, CHP, DMSO, and TBP, respectively, for a rotation speed of 1000 rpm. (e)-(h) The corresponding photoluminescence images. The scale bars correspond to 200 µm.

Figure 5 from the ACS Omega article — **Figure 5.** (A) UV-vis absorption spectra and (B) photoluminescence spectra of the sample areas of Figure 4, corresponding to samples NA, CHP, DMSO, and TBP.

Figure 6 from the ACS Omega article — **Figure 6.** Optical microscopy images of crystals synthesized by increasing concentrations of CHP additive: (a) 5, (b) 15, (c) 25, (d) 50, and (e) 60% v/v in DMF. The scale bars correspond to 200 µm.

Figure 7 from the ACS Omega article — **Figure 7.** (A) Average crystal size versus spin coater rotation speed obtained using 5% CHP additive in DMF. The shaded areas indicate rod- and cuboid-like growth regimes. (B) Average crystal size and rod/cuboid ratio as a function of CHP concentration.

Figure 8 from the ACS Omega article — **Figure 8.** Photoluminescence (black curve) and transmittance (red curve) spectra of (a) a plate-shaped crystal and (c) a pyramid-shaped crystal. (b, d) The corresponding optical microscopy images. The scale bars correspond to 50 µm.

Figure 9. Optical setup for transmittance and photoluminescence — **Figure 9.** Schematic representation of the setup used for measuring the optical transmittance and photoluminescence spectra, where the acronyms are lens (L), beam splitter (BS), spectrometer, and camera (CAM).

Research fields

Bottom-up

MAPbBr₃ single microcrystals are grown directly on quartz by spin coating. Rotation speed and three solvent additives are varied systematically, showing how evaporation and precursor coordination control crystal size, coverage and morphology in a simple deposition process.

Characterization

Statistical optical microscopy is combined with SEM, X-ray diffraction, absorption and photoluminescence. The measurements connect each processing condition with crystal dimensions, phase purity and emission, rather than judging growth from surface appearance alone.

RESEARCH TOPICS

MaterialsSpin coating is used here to grow isolated MAPbBr₃ microcrystals rather than a continuous polycrystalline film. SEM and optical microscopy in Figures 2 and 4 show how additive and rotation speed change the population from small grains to rods, cuboids and plates. X-ray diffraction identifies the cubic Pm3̅m phase in every sample; DMSO and CHP additionally strengthen the (110) and (210) reflections, indicating crystals preferentially oriented with those planes parallel to the substrate. This morphology control is important because fewer grain boundaries can reduce charge trapping and recombination.

SetupsThe growth study spans spin speeds from 600 to 5000 rpm and CHP concentrations from 5 to 60% by volume in DMF. Figures 6 and 7 turn the microscopy observations into quantitative trends by tracking average crystal size and the rod-to-cuboid ratio against additive concentration. Optical characterization then selects individual crystals with a microscope, switches the collected signal between a CCD camera and an iHR320 spectrometer with a liquid-nitrogen-cooled silicon detector, and records photoluminescence and transmission from the same object rather than from an ensemble.

ChemistryThe precursor contains equimolar methylammonium bromide and lead bromide in DMF. Three coordinating additives—N-cyclohexyl-2-pyrrolidone (CHP), DMSO and tert-butylpyridine—are compared because they alter nucleation and crystal growth during solvent evaporation. CHP provides particularly broad morphological control as its concentration is increased. A plate grown with CHP at 800 rpm has parallel faces measuring about 20.64 × 21.62 μm and an optically fitted thickness of 1.5 μm; its transmission fringes above roughly 550 nm show that the chemically grown crystal also functions as a Fabry–Pérot microcavity.