Multi-cation Synergy Suppresses Phase Segregation in Mixed-Halide Perovskites

Dang, Hoang X.; Wang, Kai; Ghasemi, Masoud; Tang, Maochun; Bastiani, Michele De; Aydın, Erkan; Dauzon, Emilie; Barrit, Dounya; Peng, Jun; Smilgies, Detlef‐M.; Wolf, Stefaan De; Amassian, Aram

doi:10.1016/j.joule.2019.05.016

Cited by 190 publications

(210 citation statements)

References 47 publications

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“…It's clear that the 3C (100) phase is already present in the case of the as‐cast FA 0.81 MA 0.14 Cs 0.05 PbI 2.55 Br 0.45 film but is not formed until annealing to ≈125 °C in the case of the FAPbI 3 film. This result confirms the facile in situ formation of the desired 3C phase in the mixed halide formulation, in agreement with a recent study comparing the in situ and thermal conversions of various mixed halide mixed cation perovskites …”

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confidence: 92%

Kinetic Stabilization of the Sol–Gel State in Perovskites Enables Facile Processing of High‐Efficiency Solar Cells

et al. 2019

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With record power conversion efficiencies (PCE) close to 24%, perovskite solar cells (PSCs) hold great promise to combine high photovoltaic performance with low processing cost. [1][2][3][4] This combination can be ascribed to several factors, such as the remarkable optoelectronic properties of perovskites-evidenced by a sharp absorption onset, a small Urbach energy, and a low exciton binding energy-as well as the fact that perovskites use earth-abundant elements. [5][6][7] The organic-inorganic metal halide perovskites used in such devices feature the characteristic AMX 3 structure, where A is an organic or inorganic cation, most often methylammonium (CH 3 NH 3 + , MA + ), formamidinium (HC(NH 2 ) 2 + , FA + ), or cesium (Cs + ), M is a metal cation, such as Pb 2+ or Sn 2+ , and X is a monovalent anion (halide ion Cl, Br, or I). [8][9][10] Various deposition techniques have been developed to obtain polycrystalline perovskite films, including spin-, dip-, and blade-coating, as well as vacuumbased processes. [11,12] To date, one-step spin coating remains the most popular and facile implementation to fabricate high-quality hybrid perovskite thin films from solution. The device efficiency and stability are strongly dictated by the electronic properties and trap state densities in the perovskite film. These, in turn, are influenced by the film crystallization, its morphology, and the presence of defects and imperfections. [13,14] However, despite the simplicity of the one-step deposition, the exact mechanisms underlying the growth process, from precursor solution to solid-state film, and the crystallization mechanism within the sol-gel state, are still poorly understood. This lack of information is partially caused by the heavy reliance on post-deposition ex situ characterization methods to date. [15,16] Recently, in situ time-resolved grazing-incidence wide-angle X-ray scattering (GIWAXS) has emerged as a powerful technique to study the microstructural evolution from the solution-precursor to the solid state, revealing the crystallization behavior and formation of crystalline intermediates and byproducts. [17,18] Using in situ GIWAXS methods, the classic MAPbI 3 perovskite material has already been investigated; Gong and coworkers identified the Perovskite solar cells increasingly feature mixed-halide mixed-cation compounds (FA 1−x−y MA x Cs y PbI 3−z Br z ) as photovoltaic absorbers, as they enable easier processing and improved stability. Here, the underlying reasons for ease of processing are revealed. It is found that halide and cation engineering leads to a systematic widening of the anti-solvent processing window for the fabrication of high-quality films and efficient solar cells. This window widens from seconds, in the case of single cation/ halide systems (e.g., MAPbI 3 , FAPbI 3 , and FAPbBr 3 ), to several minutes for mixed systems. In situ X-ray diffraction studies reveal that the processing window is closely related to the crystallization of the disordered sol-gel and to the number of crystalline byprodu...

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confidence: 92%

Kinetic Stabilization of the Sol–Gel State in Perovskites Enables Facile Processing of High‐Efficiency Solar Cells

et al. 2019

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“…This moisture degradation mechanism is proposed based on excessive halide‐deficient defects than Pb‐related defects at the film surface, resulting from the incomplete conversion of intermediate phases. [ 9 ]…”

Section: Resultsmentioning

confidence: 99%

“…Moreover, a wide antisolvent processing window is beneficial to prepare reproducible MLMP films. [ 8,9 ] Therefore, MLMPs have been established as ideal candidates in PSCs with the remarkable PCE and long‐term stability.…”

Section: Introductionmentioning

confidence: 99%

Multifunctional Phosphorus‐Containing Lewis Acid and Base Passivation Enabling Efficient and Moisture‐Stable Perovskite Solar Cells

Yang

Dou

Kou

et al. 2020

Adv Funct Materials

175

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Multiple-cation lead mixed-halide perovskites (MLMPs) have been recognized as ideal candidates in perovskite solar cells in terms of high efficiency and stability due to decreased open-circuit voltage loss and suppressed yellow phase formation. However, they still suffer from an unsatisfactory long-term moisture stability. In this study, phosphorus-containing Lewis acid and base molecules are employed to improve device efficiency and stability based on their multifunction including recombination reduction, phase segregation suppression, and moisture resistance. The strong fluorine-containing Lewis acid treatment can achieve a champion PCE of 22.02%. Unencapsulated and encapsulated devices retain 63% and 80% of the initial efficiency after 14 days of aging under 75% and 85% relative humidity, respectively. The better passivation of Lewis acid implies more halide defects than Pb defects at the MLMP surface. This unbalanced defect type results from phase segregation that is the synergistic effect of Cs and halide ion migrations. Identifying defect type based on different passivation effects is beneficial to not only choose suitable passivators to boost the efficiency and slow down the moisture degradation of MLMP solar cells, but also to understand the mechanism of defect-assisted moisture degradation.

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“…The role of cyano groups on the passivation of mixed‐cation mixed‐halide perovskites (FA 0.81 MA 0.14 Cs 0.05 PbI 2.55 Br 0.45 ) was systematically studied due to their high reproducibility and phase stability. [ 24 ] We demonstrate that SM2 molecule, which has two cyano groups as the end, is present throughout the entire depth of the perovskite films, suggesting its location in the grain boundaries. The density functional theory (DFT) calculations and experimental results suggest that the SM2 molecule with two cyano groups creates a stronger binding to surface undercoordinated Pb 2+ compared to the SM1 molecule (with only one cyano group), minimizing the deep trap states in the perovskite layer.…”

Section: Introductionmentioning

confidence: 92%

Defect Passivation in Perovskite Solar Cells by Cyano‐Based π‐Conjugated Molecules for Improved Performance and Stability

Wang

Liu

Yin

et al. 2020

Adv Funct Materials

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106

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Defects at the surface and grain boundaries of metal–halide perovskite films lead to performance losses of perovskite solar cells (PSCs). Here, organic cyano‐based π‐conjugated molecules composed of indacenodithieno[3,2‐b]thiophene (IDTT) are reported and it is found that their cyano group can effectively passivate such defects. To achieve a homogeneous distribution, these molecules are dissolved in the antisolvent, used to initiate the perovskite crystallization. It is found that these molecules are self‐anchored at the grain boundaries due to their strong binding to undercoordinated Pb2+. On a device level, this passivation scheme enhances the charge separation and transport at the grain boundaries due to the well‐matched energetic levels between the passivant and the perovskite. Consequently, these benefits contribute directly to the achievement of power conversion efficiencies as high as 21.2%, as well as the improved environmental and thermal stability of the PSCs. The surface treatment provides a new strategy to simultaneously passivate defects and enhance charge extraction/transport at the device interface by manipulating the anchoring groups of the molecules.

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Multi-cation Synergy Suppresses Phase Segregation in Mixed-Halide Perovskites

Cited by 190 publications

References 47 publications

Kinetic Stabilization of the Sol–Gel State in Perovskites Enables Facile Processing of High‐Efficiency Solar Cells

Kinetic Stabilization of the Sol–Gel State in Perovskites Enables Facile Processing of High‐Efficiency Solar Cells

Multifunctional Phosphorus‐Containing Lewis Acid and Base Passivation Enabling Efficient and Moisture‐Stable Perovskite Solar Cells

Defect Passivation in Perovskite Solar Cells by Cyano‐Based π‐Conjugated Molecules for Improved Performance and Stability

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