Precise Control of Perovskite Crystallization Kinetics via Sequential A‐Site Doping

Abstract

film deposition process to achieve desired morphology and microstructure. [2-6] Most of the high-efficiency PSCs were produced by either one-step or two-step fabrication methods. The very first MAPbI 3-based PSC was fabricated via a one-step spincoating process developed by Kojima et al. in 2009. [7] However, the one-step fabricated perovskite film typically exhibited a dendritic morphology with poor coverage. To address the morphology issue, a two-step spin-coating process was developed by Xiao et al. [8] and Im et al. [9] in 2014, which consisted of sequential depositions of an inorganic PbI 2 layer and an organic salt MAI. This two-step method gave rise to compact and pinhole-free MAPbI 3 perovskite films, significantly increasing the efficiency of MA-based PSCs to ≈17%. [9] In 2015, the record PCE received another boost through the development of a simpler antisolvent-assisted one-step method, which could form a very uniform perovskite thin film by promoting the crystallization process. [4,10] Meanwhile, MA cations were replaced by CH(NH 2) 2 + (FA) cations to improve the light Two-step-fabricated FAPbI 3-based perovskites have attracted increasing attention because of their excellent film quality and reproducibility. However, the underlying film formation mechanism remains mysterious. Here, the crystallization kinetics of a benchmark FAPbI 3-based perovskite film with sequential A-site doping of Cs + and GA + is revealed by in situ X-ray scattering and first-principles calculations. Incorporating Cs + in the first step induces an alternative pathway from δ-CsPbI 3 to perovskite α-phase, which is energetically more favorable than the conventional pathways from PbI 2. However, pinholes are formed due to the nonuniform nucleation with sparse δ-CsPbI 3 crystals. Fortunately, incorporating GA + in the second step can not only promote the phase transition from δ-CsPbI 3 to the perovskite α-phase, but also eliminate pinholes via Ostwald ripening and enhanced grain boundary migration, thus boosting efficiencies of perovskite solar cells over 23%. This work demonstrates the unprecedented advantage of the two-step process over the one-step process, allowing a precise control of the perovskite crystallization kinetics by decoupling the crystal nucleation and growth process.

Metal‐Halide Perovskite Crystallization Kinetics: A Review of Experimental and Theoretical Studies

“…Reproduced with permission. [50] Copyright 2020, Wiley-VCH. g) Activation energies of the αand δ-phase of FAPbI 3 in the dependence of OH − concentration.…”

“…By adopting DFT simulation, Qin et al revealed that the incorporation of GA + into CsPbI 3 is not only beneficial for promoting the phase transition from δ-CsPbI 3 to the perovskite α-phase, but also favorable for eliminating pinholes via Ostwald ripening and inhibiting grain boundary migration (Figure 1f). [50] Chen et al simulated that a low OH − concentration will make δ-phase FAPbI 3 a much higher activation energy of 5.352 eV compared to the α-phase FAPbI 3 (3.518 eV), which is favorable for the fabrication of pure α-phase FAPbI 3 (Figure 1g). [51] With the increasing of OH − concentration, the activation energies of δ-phase FAPbI 3 will decrease from 5.352 to 4.143 eV.…”

“…The bond order of FA + is the average value of all FA + cations, and the average bond order is that of all FA + , Cs + , and GA + cations. Reproduced with permission [50]. Copyright 2020, Wiley-VCH.…”

Dual‐function interface engineering for efficient perovskite solar cells

“…Due to their low cost and high power conversion efficiencies, lead halide perovskite solar cells (PSCs) have become promising technology for future clean energy harvesting. [1][2][3][4][5][6] Currently, the most popular PSCs are planar ones, in which the active perovskite film is sandwiched between an electron transport layer (ETL) and hole transport layer (HTL). In the standard architecture of the planar PSCs (ITO/ETL/perovskite/HTL/Au), the most widely used HTL (ETL) is Spiro-OMeTAD (SnO 2 ).…”

Trifluoromethylphenylacetic Acid as In Situ Accelerant of Ostwald Ripening for Stable and Efficient Perovskite Solar Cells

“…Generally, researchers utilize interface engineering, solvent engineering, crystalline engineering, additive engineering, composition engineering, and so on to improve efficiency and stability, and prevent lead leakage by adsorption and/or encapsulation with organic compounds. [ 13–22 ]…”