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ACS Appl Mater Interfaces. 2016 Nov 30;8(47):32366-32375. Epub 2016 Nov 18.

Facet-Dependent Property of Sequentially Deposited Perovskite Thin Films: Chemical Origin and Self-Annihilation.

Author information

1
Department of Electronic Engineering, The Chinese University of Hong Kong , Shatin, New Territories, Hong Kong SAR, People's Republic of China.
2
Shenzhen Institute of Advanced Technology, Chinese Academy of Science , Shenzhen, 518055, People's Republic of China.
3
Siyuan Laboratory, Guangzhou Key Laboratory of Vacuum Coating Technologies and New Energy Materials, Department of Physics, Jinan University , Guangzhou, Guangdong 510632, People's Republic of China.
4
National Laboratory of Solid State Microstructures & Department of Physics, Nanjing University , Nanjing 210093, People's Republic of China.

Abstract

Quantification of intergrain length scale properties of CH3NH3PbI3 (MAPbI3) can provide further understanding of material physics, leading to improved device performance. In this work, we noticed that two typical types of facets appear in sequential deposited perovskite (SDP) films: smooth and steplike morphologies. By mapping the surface potential as well as the photoluminescence (PL) peak position, we revealed the heterogeneity of SDP thin films that smooth facets are almost intrinsic with a PL peak at 775 nm, while the steplike facets are p-type-doped with 5-nm blue-shifted PL peak. Considering the reaction process, we propose that the smooth facets have well-defined crystal lattices that resulted from the interfacial reaction between MAI and PbI2 domains containing low trap states density. The steplike facets are MAI-rich originated from the grain boundaries of PbI2 film and own more trap states. Conversion of steplike facets to smooth facets can be controlled by increasing the reaction time through Ostwald ripening. The improved stability, photoresponsivity up to 0.3 A/W, on/off ratio up to 3900, and decreased photo response time to ∼160 μs show that the trap states can be annihilated effectively to improve the photoelectrical conversion with prolonged reaction time and elimination of steplike facets. Our findings demonstrate the relationship between the facet heterogeneity of SDP films and crystal growth process for the first time, and imply that the systematic control of crystal grain modification will enable amelioration of crystallinity for more-efficient perovskite photoelectrical applications.

KEYWORDS:

MAI rich; Ostwald ripening; facet heterogeneity; sequential deposited perovskite; trap states annihilation

PMID:
27933852
DOI:
10.1021/acsami.6b11986

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