High-Performance Formamidinium-Based Perovskite Solar Cells via Microstructure-Mediated ..delta..-to-..alpha.. Phase Transformation

Tanghao Liu, Yingxia Zong, Yuanyuan Zhou, Mengjin Yang, Zhen Li, Onkar S. Game, Kai Zhu, Rui Zhu, Qihuang Gong, Nitin P. Padture

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98 Scopus Citations


The δ → α phase transformation is a crucial step in the solution-growth process of formamidinium-based lead triiodide (FAPbI3) hybrid organic-inorganic perovskite (HOIP) thin films for perovskite solar cells (PSCs). Because the addition of cesium (Cs) stabilizes the α phase of FAPbI3-based HOIPs, here our research focuses on FAPbI3(Cs) thin films. We show that having a large grain size in the δ-FAPbI3(Cs) non-perovskite intermediate films is essential for the growth of high-quality α-FAPbI3(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-FAPbI3(Cs) thin films suppresses grain coarsening, precluding the formation of voids at the final α-FAPbI3(Cs)-substrate interfaces. PSCs based on the interface void-free α-FAPbI3(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-FAPbI3(Cs) intermediate films, which are subsequently converted to coarse-grained, high-quality α-FAPbI3(Cs) HOIP thin films. This study highlights the importance of microstructure meditation in the processing of formamidinium-based PSCs.

Original languageAmerican English
Pages (from-to)3246-3250
Number of pages5
JournalChemistry of Materials
Issue number7
StatePublished - 11 Apr 2017

Bibliographical note

Publisher Copyright:
© 2017 American Chemical Society.

NREL Publication Number

  • NREL/JA-5900-68540


  • organic-inorganic
  • perovskite thin films
  • phase transformation
  • solar cells


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