Journal
ADVANCED MATERIALS
Volume 32, Issue 4, Pages -Publisher
WILEY-V C H VERLAG GMBH
DOI: 10.1002/adma.201904702
Keywords
A-site management; A-site-related defects; highly crystalline perovskites; placeholder cations; transient phases
Categories
Funding
- National Key Research and Development Program of China [2018YFA0703503, 2016YFA0202701]
- Overseas Expertise Introduction Projects for Discipline Innovation (111 project) [B14003]
- National Natural Science Foundation of China [51527802, 51702014, 51902021]
- Postdoctoral Research Foundation of China [2019M650488]
- State Key Laboratory for Advanced Metals and Materials [2018Z-03, 2019Z-04]
- Fundamental Research Funds for the Central Universities [FRF-TP-18-042A1, FRF-AS-17-002, FRF-TP-19-005A2]
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An in-depth understanding and effective suppression of nonradiative recombination pathways in perovskites are crucial to their crystallization process, in which supersaturation discrepancies at different time scales between CH3NH3I (MAI, methylammonium iodide) and PbI2 remain a key issue. Here, an A-site management strategy via the introduction of an A-site placeholder cation, NH4+, to offset the deficient MA(+) precipitation by occupying the cavity of Pb-I framework, is proposed. The temporarily remaining NH4+ is substituted by subsequently precipitated MA(+). The temperature-dependent crystallization process with the generation and consumption of a transient phase is sufficiently demonstrated by the dynamic changes in crystal structure characteristic peaks through in situ grazing-incidence X-ray diffraction and the surface potential difference evolution through temperature-dependent Kelvin probe force microscopy. A highly crystalline perovskite is consequently acquired, indicated by the enlarged grain size, lowered nonradiative defect density, prolonged carrier lifetime, and fluorescence lifetime imaging. Most importantly, it is identified that the A-site I-MA defect is responsible for such crystal quality optimization based on theoretical calculations, transient absorption, and deep-level transient spectroscopy. Furthermore, the universality of the proposed A-site management strategy is demonstrated with other mixed-cation perovskite systems, indicating that this methodology successfully provides guidance for synthesis route design of highly crystalline perovskites.
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