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Title: High-performance formamidinium-based perovskite solar cells via microstructure-mediated δ-to-α phase transformation

The δ → α phase transformation is a crucial step in the solution-growth process of formamidinium-based lead triiodide (FAPbI 3) hybrid organic–inorganic perovskite (HOIP) thin films for perovskite solar cells (PSCs). Because the addition of cesium (Cs) stabilizes the α phase of FAPbI 3-based HOIPs, here our research focuses on FAPbI 3(Cs) thin films. We show that having a large grain size in the δ-FAPbI 3(Cs) non-perovskite intermediate films is essential for the growth of high-quality α-FAPbI 3(Cs) HOIP thin films. Here grain coarsening and phase transformation occur simultaneously during the thermal annealing step. A large starting grain size in the δ-FAPbI 3(Cs) thin films suppresses grain coarsening, precluding the formation of voids at the final α-FAPbI 3(Cs)–substrate interfaces. PSCs based on the interface void-free α-FAPbI 3(Cs) HOIP thin films are much more efficient and stable in the ambient atmosphere. This interesting finding inspired us to develop a simple room-temperature aging method for preparing coarse-grained δ-FAPbI 3(Cs) intermediate films, which are subsequently converted to coarse-grained, high-quality α-FAPbI 3(Cs) HOIP thin films. As a result, this study highlights the importance of microstructure meditation in the processing of formamidinium-based PSCs.
Authors:
 [1] ;  [2] ;  [3] ;  [4] ;  [4] ;  [3] ; ORCiD logo [4] ;  [5] ;  [5] ;  [3]
  1. Peking Univ., Beijing (China); Brown Univ., Providence, RI (United States); National Renewable Energy Lab. (NREL), Golden, CO (United States)
  2. Brown Univ., Providence, RI (United States); Qingdao Univ. of Science and Technology, Qingdao (People's Republic of China)
  3. Brown Univ., Providence, RI (United States)
  4. National Renewable Energy Lab. (NREL), Golden, CO (United States)
  5. Peking Univ., Beijing (China); Shanxi Univ., Shanxi (People's Republic of China)
Publication Date:
Report Number(s):
NREL/JA-5900-68540
Journal ID: ISSN 0897-4756
Grant/Contract Number:
AC36-08GO28308
Type:
Accepted Manuscript
Journal Name:
Chemistry of Materials
Additional Journal Information:
Journal Volume: 29; Journal Issue: 7; Journal ID: ISSN 0897-4756
Publisher:
American Chemical Society (ACS)
Research Org:
National Renewable Energy Lab. (NREL), Golden, CO (United States)
Sponsoring Org:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Country of Publication:
United States
Language:
English
Subject:
14 SOLAR ENERGY; 36 MATERIALS SCIENCE; phase transformation; organic-inorganic; perovskite thin films; solar cells
OSTI Identifier:
1358335