The Making and Breaking of Lead-Free Double Perovskite Nanocrystals of Cesium Silver–Bismuth Halide Compositions

Bekenstein, Yehonadav; Dahl, Jakob; Huang, Jin‐Shun; Osowiecki, Wojciech T.; Swabeck, Joseph K.; Chan, Emory M.; Yang, Peidong; Alivisatos, A. Paul

doi:10.1021/acs.nanolett.8b00560

Cited by 288 publications

(338 citation statements)

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“…As shown in Figure a, a sharp absorption peak centered at ≈450 nm is observed, which is not from the quantum confined excitonic transition since there is no obvious size‐dependence of the absorption peak as reported . A recent report pointed out that this sharp peak may be assigned to a direct bismuth s–p transition . The film also exhibits an absorption tail extending to 800 nm.…”

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confidence: 55%

High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells

et al. 2018

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Lead‐free double perovskites have been demonstrated as promising alternatives to solve the toxicity and stability issues in conventional lead trihalide perovskites. However, different solubility of components in the precursors hinders fabrication of double perovskite films with commonly used solution procedures. Here, for the first time, the authors successfully prepared double perovskite Cs2AgBiBr6 thin films throughout a sequential‐vapor‐deposition procedure. The obtained thin films with pure double perovskite phase show large grain sizes, uniform, and smooth surface properties. In addition, the high‐quality vapor‐deposited Cs2AgBiBr6 films exhibit a photoluminescence (PL) lifetime of 117 ns, indicative of significant potential in photovoltaic applications. The resulting solar cells with planar device structure show an optimized power conversion efficiency of 1.37%, which can be maintained at 90% after 240 h of storage under ambient condition. Our results demonstrate the feasibility of employing vapor deposition technique to fabricate high‐quality double perovskite thin films, which paves the way for further development of various optoelectronic devices based on these promising lead‐free semiconductors.

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confidence: 55%

High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells

et al. 2018

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“…[137] The presence of Ag 4d states in the compound is known to play a role in reducing the bandgap and is partially responsible for the indirect bandgap of Cs 2 AgBiX 6 (X = Cl, Br, and I). [139] This peak is blue shifted (more than 1 eV) from the band edge. [111] This bandgap value is 0.57 eV higher than that of bulk Cs 2 AgBiBr 6 (1.95 eV).…”

Section: + /Bi 3+ Halide Double Perovskitesmentioning

confidence: 94%

Progress of Lead‐Free Halide Double Perovskites

Igbari

Wang

Liao

2019

Advanced Energy Materials

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Although impressive performance has been obtained, PSCs are still far from commercial or real-life availability due to serious issues such as toxicity [15,16] and poor stability to heat, [17] oxygen, [18] moisture, [19,20] electric field, [21] and light. [18,22] The toxic nature of hybrid organic-inorganic lead halide perovskites has been traced to the presence of Pb in its chemical composition. [15,16,[23][24][25] Pb 2+ readily dissolves in water (e.g., rain water) to form a toxic solution capable of causing serious environmental pollution, harmful to human beings and the ecosystem. Besides their sensitivity to moisture, oxygen, light, electric field, or thermal stress, an existing self-degradation pathway [26,27] is also a big issue in hybrid organic-inorganic lead halide perovskites. Mixed-halide and mixed-cation perovskites have been investigated to address these issues. [28][29][30][31][32] The group IV elements, tin (Sn) [23,[33][34][35] and germanium (Ge), [34,36] have been employed as the replacements for Pb. However, the device performance through this approach has fallen short of the Pb-based ones. For example, the PCEs reported for Sn-based perovskite solar cells are usually less than 10%. [23,[33][34][35][37][38][39][40] In addition, the easy oxidation of Sn and Ge from the +2 state to the +4 state due to their high energy 5s and 4s orbitals makes them less promising for application in stable and long-term PSCs. [41] High throughput calculations also demonstrate that these substitutions are likely to compromise the ideal optoelectronic properties of MAPbI 3 . [42,43] Furthermore, low dimensional (e.g., 2D, 1D, and 0D) perovskites have also been used to address the stability issues in PSCs. [44][45][46][47][48] Recently, a stabilized PCE of 21.7% resulting from a 2D/3D bilayer PSC was reported. [49] However, the highest certified PCE in a 2D-only planar PSC is 15.3%, [50] which is far below that of their 3D perovskite-based counterparts. It thus stimulates the interest to develop new classes of materials which can solve the issues of toxicity and stability while still maintaining the fascinating properties of lead-based perovskite materials.Recent theoretical calculations demonstrate that a halide double perovskite structure, A 2 B′B″X 6 , which could be formed through a replacement of two toxic Pb 2+ in the crystal lattice with a pair of nontoxic heterovalent (i.e., monovalent and trivalent) metal cations, is a promising alternative to realize high-performance, lead-free, and stable PSCs. [51,52] Although, spectroscopic limited maximum efficiency (SLME) calculations revealed an efficiency limit less than 8% for the most prominent member www.advancedsciencenews.com double perovskites with a vacancy ordered structure. [88] In particular, the unit cell axis of Cs 2 AgBiBr 6 is given to be ≈11.25 Å, [25] which is two times larger than that of MAPbBr 3 (≈5.92 Å). [89] Both Ag + and Bi 3+ occupy the B-site of the crystal lattice with slightly varied metal-halide bond lengths. The dissimilar bond lengths st...

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“…[55] Second, for B(III) cations, the transition metal cations with multiple oxidation states and/or partially occupied d or f orbitals are not desirable for designing photovoltaic absorbers, because they may introduce deep defect states and too localized band edges. Largesize single crystals, [155,[172][173][174] nanocrystals, [175][176][177][178] and highquality films [179][180][181][182] The element Au is half-colored because it exists only in the compounds A 2 Au 2 X 6 with A = Rb, Cs and X = Cl, Br, I. Most of the reported double perovskites are fluorides and chlorides, [158,159] which generally have too large bandgaps for photovoltaic applications.…”

Section: D a 2 B(i)b(ii)x 6 Halide Double Perovskitesmentioning

confidence: 99%

From Lead Halide Perovskites to Lead‐Free Metal Halide Perovskites and Perovskite Derivatives

2019

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serious challenges due to the inclusion of toxic Pb and instability against moisture, heat, and irradiation. In recent years, significant efforts have been paid to develop Pb-free halide perovskite and perovskite derivative absorber materials. However, so far, solar cells based on these materials show significantly inferior performances as compared to their Pb halide perovskite counterparts. Herein, we provide reviews on the fundamental understandings of the photovoltaic properties from Pb halide perovskites to Pb-free metal halide perovskites and perovskite derivatives as well as the experimental results reported in the literature. The results suggest that replacing Pb by nontoxic elements may degrade the superior photovoltaic properties seen in Pb halide perovskites, explaining the fact that all reported solar cells based on Pb-free perovskites or perovskite derivatives show performances significantly lower than Pb halide perovskite solar cells. Overview: Approaches and Consequences of Pb ReplacementWe first provide an overview of the approaches and consequences of Pb replacement reported in the literature, as shown in Figure 1. In general, there are two categories for Pb replacement: using either homovalent elements such as Sn and Ge or heterovalent elements such as Bi and Sb. The heterovalent replacement category can be divided into two subcategories based on the ways to maintain the charge neutrality: ion-splitting and ordered vacancy. The ion-splitting subcategory can be further divided into mixed anion compounds with the formula of AB(Ch,X) 3 , where Ch represents a chalcogen element, and X represents a halogen element, and mixed cation compounds with a formula of A 2 B(I)B(III)X 6 , which are commonly called double perovskites. The ordered vacancy subcategory can also be divided into the B(III) compounds with a formula of A 3 ◻B(III)X 9 and the B(IV) compounds with a formula of A 2 ◻ B(IV)X 6 (the sign of ◻ indicates vacancy). Figure 1 also summarizes the photovoltaic properties and the stabilities of each group of materials, which provides a clear overview of the consequences of Pb replacement. While the homovalent replacement by Sn or Ge leads to instability, the heterovalent Pb replacement leads to degraded electronic properties mainly due to the reduction on electronic dimensionality. As a result, all the reported Pb-free perovskite and perovskite derivative solar Despite the exciting progress on power conversion efficiencies, the commercialization of the emerging lead (Pb) halide perovskite solar cell technology still faces significant challenges, one of which is the inclusion of toxic Pb. Searching for Pb-free perovskite solar cell absorbers is currently an attractive research direction. The approaches used for and the consequences of Pb replacement are reviewed herein. Reviews on the theoretical understanding of the electronic, optical, and defect properties of Pb and Pb-free halide perovskites and perovskite derivatives are provided, as well as the experimental results available in the literature....

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The Making and Breaking of Lead-Free Double Perovskite Nanocrystals of Cesium Silver–Bismuth Halide Compositions

Cited by 288 publications

References 40 publications

High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells

High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells

Progress of Lead‐Free Halide Double Perovskites

From Lead Halide Perovskites to Lead‐Free Metal Halide Perovskites and Perovskite Derivatives

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The Making and Breaking of Lead-Free Double Perovskite Nanocrystals of Cesium Silver–Bismuth Halide Compositions

Cited by 288 publications

References 40 publications

High‐Quality Sequential‐Vapor‐Deposited Cs2AgBiBr6 Thin Films for Lead‐Free Perovskite Solar Cells

High‐Quality Sequential‐Vapor‐Deposited Cs2AgBiBr6 Thin Films for Lead‐Free Perovskite Solar Cells

Progress of Lead‐Free Halide Double Perovskites

From Lead Halide Perovskites to Lead‐Free Metal Halide Perovskites and Perovskite Derivatives

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High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells

High‐Quality Sequential‐Vapor‐Deposited Cs₂AgBiBr₆ Thin Films for Lead‐Free Perovskite Solar Cells