Controlling Thin-Film Stress and Wrinkling during Perovskite Film Formation

TLDR

Perovskite film deposition has been optimized for uniformity and high efficiencies, yet the evolution of thin‑film stress and its impact on surface morphology—particularly the trade‑off between textured light‑scattering surfaces and smooth, pinhole‑free contact layers—has received limited attention. The study reveals that antisolvent conversion induces in‑plane compressive stress that causes wrinkling and deep trenches, and that slowing the conversion rate suppresses wrinkling, yielding ultrasmooth films.

Abstract

Significant effort has focused on controlling the deposition of perovskite films to enable uniform films, enabling efficiencies to climb dramatically. However, little attention has been paid to the evolution of thin-film stresses during deposition and the consequent effect on film morphology. While a textured surface topology has potential benefits for light scattering, a smooth surface is desirable to enable the pinhole-free deposition of contact layers. We show that the highly textured morphology made by popular antisolvent conversion methods arises because of in-plane compressive stress experienced during the intermediate phase of film formation where the substrate constrains the film from expanding—leading to energy release in the form of wrinkling, resulting in trenches that can be hundreds of nanometers deep with periods of several micrometers. We demonstrate that the extent of wrinkling is correlated with the rate of film conversion and that ultrasmooth films are obtained by slowing the rate of film formation.