Crystallisation of CH 3 NH 3 PbX 3 (X = I, Br, and Cl) trihalide perovskite using PbI 2 and PbCl 2 precursors

Abstract

In this work, the effects of halides on the properties of mixed-halide perovskite films are investigated. The films were prepared by sequential deposition two-step technique. PbI 2 or PbI 2 -PbCl 2 solution was first spin-coated on fluorine-doped tin oxide glasses, and CH 3 NH 3 (I x Br y ) solution, with different molar ratio of I - and Br - (1:0, 2:1, 4:1, 1:4, 1:2, and 0:1), was subsequently coated on top. Then, the films were annealed at 90°C for 1 h and 100°C for 25 min to transform into perovskite structure. The characterisation of perovskite films included X-ray diffraction, ultraviolet-visible spectroscopy, photoluminescence spectroscopy, and scanning electron microscopy. The results indicated that the incorporation of Br - and/or Cl - in iodine-based perovskites, i.e. CH 3 NH 3 Pb(I 1-x Br x ) 3 and CH 3 NH 3 Pb(I 1-x-y Br x Cl y ) 3 , would enlarge their bandgap. However, with the use of PbI 2 precursor, excess PbI 2 occurred and resulted in minor affects on the structural and optical properties. The use of PbCl 2 as chlorine source was also found to affect the quality of the film morphology. The analysis in this study could provide another insightful aspect for understanding the role of halides in the synthesis of mixed-halide perovskites.