Manipulating the Mixed-Perovskite Crystallization Pathway Unveiled by In Situ GIWAXS

Minchao Qin, Kinfai Tse, Tsz Ki Lau, Yuhao Li, Chun Jen Su, Guang Yang, Jiehuan Chen, Junyi Zhu, U. Ser Jeng, Gang Li, Hongzheng Chen, Xinhui Lu

Research output: Journal article publicationJournal articleAcademic researchpeer-review

60 Citations (Scopus)

Abstract

Mixed perovskites have achieved substantial successes in boosting solar cell efficiency, but the complicated perovskite crystal formation pathway remains mysterious. Here, the detailed crystallization process of mixed perovskites (FA0.83MA0.17Pb(I0.83Br0.17)3) during spin-coating is revealed by in situ grazing-incidence wide-angle X-ray scattering measurements, and three phase-formation stages are identified: I) precursor solution; II) hexagonal δ-phase (2H); and III) complex phases including hexagonal polytypes (4H, 6H), MAI–PbI2–DMSO intermediate phases, and perovskite α-phase. The correlated device performance and ex situ characterizations suggest the existence of an “annealing window” covering the duration of stage II. The spin-coated film should be annealed within the annealing window to avoid the formation of hexagonal polytypes during the perovskite crystallization process, thus achieving a good device performance. Remarkably, the crystallization pathway can be manipulated by incorporating Cs+ ions in mixed perovskites. Combined with density functional theory calculations, the perovskite system with sufficient Cs+ will bypass the formation of secondary phases in stage III by promoting the formation of α-phase both kinetically and thermodynamically, thereby significantly extending the annealing window. This study provides underlying reasons of the time sensitivity of fabricating mixed-perovskite devices and insightful guidelines for manipulating the perovskite crystallization pathways toward higher performance.

Original languageEnglish
Article number1901284
JournalAdvanced Materials
Volume31
Issue number25
DOIs
Publication statusPublished - 20 Jun 2019

Keywords

  • annealing window
  • crystallization pathways
  • Cs doping
  • in situ GIWAXS
  • perovskite solar cells

ASJC Scopus subject areas

  • Materials Science(all)
  • Mechanics of Materials
  • Mechanical Engineering

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