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Title: Thin-Film Transformation of NH 4 PbI 3 to CH 3 NH 3 PbI 3 Perovskite: A Methylamine-Induced Conversion-Healing Process
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Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
Angewandte Chemie International Edition
Page Range / eLocation ID:
14723 to 14727
Medium: X
Sponsoring Org:
National Science Foundation
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  1. Abstract

    With power conversion efficiencies now exceeding 25%, hybrid perovskite solar cells require deeper understanding of defects and processing to further approach the Shockley‐Queisser limit. One approach for processing enhancement and defect reduction involves additive engineering—, e.g., addition of MASCN (MA = methylammonium) and excess PbI2have been shown to modify film grain structure and improve performance. However, the underlying impact of these additives on transport and recombination properties remains to be fully elucidated. In this study, a newly developed carrier‐resolved photo‐Hall (CRPH) characterization technique is used that gives access to both majority and minority carrier properties within the same sample and over a wide range of illumination conditions. CRPH measurements on n‐type MAPbI3films reveal an order of magnitude increase in carrier recombination lifetime and electron density for 5% excess PbI2added to the precursor solution, with little change noted in electron and hole mobility values. Grain size variation (120–2100 nm) and MASCN addition induce no significant change in carrier‐related parameters considered, highlighting the benign nature of the grain boundaries and that excess PbI2must predominantly passivate bulk defects rather than defects situated at grain boundaries. This study offers a unique picture of additive impact on MAPbI3optoelectronic properties as elucidated by the new CRPH approach.

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  2. ABSTRACT Methods of obtaining large grain size and high crystallinity in absorber materials play an important role in fabrication of high-performance methylammonium lead iodide (MAPbI 3 ) perovskite solar cells. Here we study the effect of adding small concentrations of Cd 2+ , Zn 2+ , and Fe 2+ salts to the perovskite precursor solution used in the single-step solution fabrication process. Enhanced grain size and crystallinity in MAPbI 3 films were obtained by using 0.1% of Cd 2+ or Zn 2+ in the precursor solution. Consequently, solar cells constructed with Cd- and Zn-doped perovskite films show a significant improvement in device performance. These results suggest that the process may be an effective and facile method to fabricate high-efficiency perovskite photovoltaic devices. 
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