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US-20260130040-A1 - ON-DEMAND FORMATION OF LEWIS BASE MOLECULES FOR EFFICIENT AND STABLE PEROVSKITE SOLAR CELLS

US20260130040A1US 20260130040 A1US20260130040 A1US 20260130040A1US-20260130040-A1

Abstract

The on-demand formation of Lewis base molecules for fabricating efficient and stable formamidinium lead iodide (FAPbI 3 )-based perovskite solar cells (PSCs). Semicarbazide hydrochloride (SECl) is incorporated as an additive in the perovskite precursor, which deprotonates to form semicarbazide (SE) molecules when needed to stabilize the intermediate 𝛿 phase. SE molecules protonate again to form SECl salt when they must be removed rapidly to accelerate the transition from the intermediate 𝛿 phase to the photovoltaic 𝛼 phase, leading to high film quality and homogeneous vertical distributions of A-site cations.

Inventors

  • Yanfa Yan
  • Sheng FU

Assignees

  • THE UNIVERSITY OF TOLEDO

Dates

Publication Date
20260507
Application Date
20251104

Claims (19)

  1. 1 . An additive for perovskite precursor solutions that comprise a lead halide precursor material, the additive comprising: a halide salt of a protonated Lewis base, wherein: the halide salt is capable of reversible acid-base disassociation; and the Lewis base is capable of coordinating with lead.
  2. 2 . The additive of claim 1 , wherein: the halide salt comprises a hydrazide compound such as semicarbazide and/or carbonohydrazide.
  3. 3 . The additive of claim 2 , wherein: the halide salt comprises at least one of semicarbazide hydrochloride (SECl) salt and carbonohydraxide hydrochloride salt.
  4. 4 . A perovskite precursor solution comprising: a lead halide precursor material; the additive of claim 1 ; and a solvent in which the halide salt is soluble.
  5. 5 . The perovskite precursor solution of claim 4 , wherein: the lead halide precursor material comprises a lead iodide-based material such as formamidinium lead iodide (FAPbI3).
  6. 6 . The perovskite precursor solution of claim 4 , wherein: the additive of claim 1 is provided at a molar ratio ranging from 0.1% to 2%, preferably about 1%, based on the amount of lead halide precursor material in the perovskite precursor solution.
  7. 7 . The perovskite precursor solution of claim 4 , wherein: the halide salt of the additive of claim 1 has an acid dissociation constant (pKa) of no greater than 4 in solution.
  8. 8 . The perovskite precursor solution of claim 4 , wherein: each solvent present in the perovskite precursor solution coordinates with lead less strongly than the Lewis base of the halide salt.
  9. 9 . The perovskite precursor solution of claim 4 , wherein: the solvent comprises an organic polar solvent such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), and combinations thereof.
  10. 10 . A method of fabricating lead halide perovskites, the method comprising the steps of: depositing a precursor solution on a substrate, the precursor solution comprising: a lead halide precursor material; a halide salt of a protonated Lewis base that is capable of reversible acid–base dissociation; and a solvent in which the halide salt is soluble; wherein at least some of the halide salt is dissolved and at least some of the Lewis base is deprotonated; subjecting the deposited precursor solution to thermal annealing to facilitate the formation of a lead halide intermediate δ phase; and effecting solvent removal from the deposited precursor solution; wherein the Lewis base, while deprotonated, coordinates with the lead in the precursor material during formation of the intermediate δ phase, thereby stabilizing it; and wherein solvent removal results in the re-protonation of the Lewis base and the reformation of the halide salt.
  11. 11 . The method of claim 10 , wherein: the thermal annealing of the deposited precursor solution is performed at a temperature less than 150 °C.
  12. 12 . The method of claim 10 , wherein: the solvent removal step comprises subjecting the deposited precursor solution to thermal annealing at a higher temperature.
  13. 13 . The method of claim 10 , wherein: the solvent removal step comprises dripping an anti-solvent onto the deposited solution.
  14. 14 . The method of claim 10 , wherein: the solvent removal step is performed such that at least 95% of the solvent is removed in 15 minutes.
  15. 15 . The method of claim 14 , wherein: the solvent removal step is performed at a temperature less than 150 °C.
  16. 16 . A method of fabricating lead halide perovskites at temperatures less than 150 °C, the method comprising the steps of: depositing a precursor solution on a substrate, the precursor solution comprising: a lead halide precursor material; semicarbazide hydrochloride (SECl) salt; and a solvent in which the halide salt is soluble; wherein at least some of the semicarbazide hydrochloride salt has decomposed into semicarbazide (SE) and hydrochloric acid (HCl); subjecting the deposited precursor solution to thermal annealing, thereby facilitating the formation of a lead halide intermediate δ phase; and effecting solvent removal from the deposited precursor solution; wherein the semicarbazide coordinates with lead in the precursor material during formation of the intermediate δ phase, thereby stabilizing it; and wherein solvent removal results in the the re-protonation of the semicarbazide and the reformation of semicarbazide hydrochloride salt.
  17. 17 . The method of claim 16 , wherein: the lead halide precursor material comprises lead iodide-based material such as formamidinium lead iodide (FAPbI3).
  18. 18 . The method of claim 16 , wherein: the solvent comprises at least one of dimethylformamide (DMF) and dimethyl sulfoxide (DMSO).
  19. 19 . The method of claim 18 , wherein: the solvent comprises both DMF and DMSO; the solvent removal step comprises performing anti-solvent dripping on the deposited precursor solution to remove at least some of the DMF; and the solvent removal step further comprises subjecting the deposited precursor solution to thermal annealing to remove at least some of the DSMO.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS This application is a nonprovisional patent application that makes a priority claim to U.S. Provisional Application No. 63/715,939. STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH This invention was made with government support under DE-EE0008753 awarded by the Department of Energy and under DE-EE0008970 awarded by the Department of Energy. The government has certain rights in the invention. FIELD The application relates to the manufacture of perovskite solar cells and, more particularly, to additives for perovskite precursor solutions that are provided for the on-demand formation of Lewis base molecules. BACKGROUND The state-of-the-art perovskite solar cells (PSCs) and modules presently employ formamidinium lead iodide (FAPbI3)-based absorbers. A small amount of inorganic A-site cations with smaller ionic sizes, such as cesium (Cs) and rubidium (Rb), are commonly added to improve the device stability and passivate the perovskite films, respectively. The manufacture of FAPbI3 and other lead halide-based PSCs generally involves the steps of preparing a precursor solution, depositing the precursor solution onto a substrate, and then performing thermal annealing to promote crystallization and solvent evaporation. Within this context, skilled artisans will appreciate that the terms “α-phase” and “δ-phase” refer to distinct crystallographic phases of the perovskite material. The α-phase is typically orthorhombic and has a well-defined crystal lattice that is conducive to efficient charge transport, making it desirable for photovoltaic applications. The δ-phase is often trigonal in structure and tends to be more disordered compared to the α-phase; it exhibits inferior performance in photovoltaic applications compared to the α-phase. To form high-quality FAPbI3 photovoltaic absorber films, a lower annealing temperature (less than 150 °C) is desirable to avoid the loss of volatile species such as iodide(I-) and formamidinium (FA+). However, at lower annealing temperatures FAPbI3 films tend to crystalize into the undesirable non-photovoltaic δ-phase; FAPbI3 films only crystalize to the desirable photovoltaic α-phase at annealing temperatures higher than 170 °C. Typically, a significant amount of methylammonium chloride (MACl) is added to promote the formation of the photovoltaic α-phase. This is undesirable since it lead to excessive material usage and because the incorporation of MA molecules into the perovskite lattice introduces a source of structural instability. It is now widely accepted that the fabrication processes must be MA-free to achieve long term cell stability. The photovoltaic FAPbI3-based α-phase typically forms through the transition from an intermediate δ phase to the photovoltaic α phase when no or a small amount of MACl additive is used. However, FAPbI3-based films fabricated by the MA-free method often exhibit two issues: (1) relatively low film quality (e.g., small grain sizes and voids at the buried interface); and (2) inhomogeneous vertical distributions of the A-site cations due to the different crystallization rates of all inorganic perovskite phases, such as CsPbI3 and RbPbI3, and FAPbI3. Inhomogeneity of the A-site cations can result in poorer power conversion efficiency (PCE) and stability of PSCs. Accordingly those skilled in the art continue with research and development efforts in the field of lead halide perovskites. SUMMARY OF THE INVENTION The present invention relates to additives for perovskite precursor solutions, and to methods of fabricating lead halide perovskite films using such additives. The invention provides an additive that includes a halide salt of a protonated Lewis base that is capable of reversible acid–base dissociation. The Lewis base component of the additive is capable of coordinating with lead, thereby influencing the crystallization and stability of the perovskite material. In certain embodiments, the halide salt comprises a hydrazide compound, such as semicarbazide and/or carbonohydrazide, and more particularly semicarbazide hydrochloride (SECl) and carbonohydrazide hydrochloride salts. The additive may be incorporated into perovskite precursor solutions that include a lead halide precursor material (e.g., formamidinium lead iodide, FAPbI₃) and a solvent in which the halide salt is soluble, such as dimethylformamide (DMF), dimethyl sulfoxide (DMSO), or mixtures thereof. The additive may be present at a molar ratio ranging from 0.1% to 2%, preferably about 1%, relative to the amount of lead halide precursor material. The halide salt preferably exhibits an acid dissociation constant (pKa) of no greater than 4 in solution, and the solvent(s) used preferably coordinate with lead less strongly than the Lewis base component of the additive. The invention further provides a method of fabricating lead halide perovskites using such precursor solutions. In the method, a precursor solution containing a lead halide precursor mater