Improved Crystallization of Lead Halide Perovskite in Two‐Step Growth Method by Polymer‐Assisted “Slow‐Release Effect”

Abstract

Fast reaction between organic salt and lead iodide always leads to small perovskite crystallites and concentrated defects. Here, polyacrylic acid is blended with organic salt, so as to regulate the crystallization in a two‐step growth method. It is observed that addition of polyacrylic acid retards aggregation and crystallization behavior of the organic salt, and slows down the reaction rate between organic salt and PbI2, by which “slow‐release effect” is defined. Such effect improves crystallization of perovskite. X‐ray diffraction study shows that, after addition of 2 mm polyacrylic acid, average crystallite size of perovskite increases from ≈40 to ≈90 nm, meanwhile, grain size increases. Thermal admittance spectroscopy study shows that trap density is reduced by nearly one order (especially for deep energy levels). Due to the improved crystallization and reduced trap density, charge recombination is obviously reduced, while lifetime of charge carriers in perovskite film and devices are prolonged, according to time‐resolved photoluminescence and transient photo‐voltage decay curve tests, respectively. Accordingly, power conversion efficiency of the device is promoted from 19.96 (±0.41)% to 21.84 (±0.25)% (with a champion efficiency of 22.31%), and further elevated to 24.19% after surface modification by octylammonium iodide.

Improved Thermal Stability and Film Uniformity of Halide Perovskite by Confinement Effect brought by Polymer Chains of Polyvinyl Pyrrolidone

“…As PAA concentration increases, crystallite size of PVSK also increases at first and then decreases. [ 36 ] Above analysis indicates that the “confinement effect” appears at relatively higher doping concentrations.…”

Stabilizing α-Phase FAPbI3 Perovskite Induced by an Ordered Solvated Quasi-Crystalline PbI2

“…Strategies to reduce defects have been proposed, such as additive (or solvent) engineering to reduce bulk defects via controlling crystallization, − post-treatment to passivate interfacial defects, , and ion substitution to control ion migration. − It was reported that low-defect density perovskite films with high crystal plane orientation were prepared by introducing the presynthesized, intrinsically highly oriented two-dimensional (2D) Dion–Jacobson perovskite of (BDA)­PbI 4 (BDA = 1,4-butanediamine) into the PbI 2 solution as a seed for three-dimensional (3D) perovskite epitaxial growth, which finally demonstrated a PCE of 23.95% . The 2D Ruddlesden–Popper perovskite of (NpMA) 2 PbI 4 (NpMAI = 1-naphthalenemethylammoniumiodide) was introduced into the PbI 2 solution to modulate crystal growth, which led to a PCE as high as 24.37% .…”

Aging‐Resistant Precursor with Ultrawide Annealing Window for 24.08% Perovskite Solar Cells

“…Meanwhile, the target films exhibited lower RMS, which is attributed to the decrease in crystallization rate, leading to improved continuity of FAI and the formation of a flat perovskite film. [ 30 ] The flat perovskite film suggests an improved interface contact between the perovskite layer and hole transport layer. Furthermore, when perovskite films prepared from precursor solutions aged for 48 h were exposed to air (15–25% RH), the original film showed partial decomposition after 42 days of exposure.…”

“…As a result, they achieved a champion PCE of 24.1%. [29] Furthermore, in the twostep sequential deposition method, the fast reaction between organic salts and PbI 2 forms a dense perovskite layer on the surface of PbI 2 , preventing further diffusion of formamidinium (FA + ) into the interior of PbI 2 and insertion into the [PbI 6 ] 4− framework, [30][31][32] resulting in the formation of low-crystallinity perovskite films. [33,34] Zhao et al manipulated PbI 2 by introducing amphiphilic ions to control the stacking direction, orientation, and distribution of the perovskite layers.…”