Crystallization in one-step solution deposition of perovskite films: Upward or downward?

Shangshang Chen; Xun Xiao; Bo Chen; Leah L Kelly; Jingjing Zhao; Yuze Lin; Michael F Toney; Jinsong Huang

doi:10.1126/sciadv.abb2412

Crystallization in one-step solution deposition of perovskite films: Upward or downward?

Sci Adv. 2021 Jan 22;7(4):eabb2412. doi: 10.1126/sciadv.abb2412. Print 2021 Jan.

Authors

Shangshang Chen¹, Xun Xiao¹, Bo Chen¹, Leah L Kelly², Jingjing Zhao¹, Yuze Lin¹, Michael F Toney^{2

3}, Jinsong Huang⁴

Affiliations

¹ Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA.
² Stanford Synchrotron Radiation Lightsource, SLAC National Accelerator Laboratory, Menlo Park, CA 94025, USA.
³ Department of Chemical and Biological Engineering, University of Colorado, Boulder, CO 80309, USA.
⁴ Department of Applied Physical Sciences, University of North Carolina at Chapel Hill, Chapel Hill, NC 27599, USA. jhuang@unc.edu.

Abstract

Despite the fast progress of perovskite photovoltaic performances, understanding the crystallization and growth of perovskite films is still lagging. One unanswered fundamental question is whether the perovskite films are grown from top (air side) to bottom (substrate side) or from bottom to top despite 10 years of development. Here, by using grazing incidence x-ray diffraction and morphology characterizations, we unveil that the perovskite films prepared by one-step solution processes, including antisolvent-assisted spin coating and blade coating, follow the downward growth from intermediate phase during thermal annealing. Such a top-to-bottom downward growth is initialized by the evaporation of residual solvent from the top surface of "wet" films and is less sensitive to perovskite compositions and the wettability of underlying substrates. Addressing this fundamental question is important to understand the heterogeneity of perovskite films along the vertical direction, which markedly affects the efficiency and stability of perovskite solar cells.

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