Controlling the Growth Kinetics and Optoelectronic Properties of 2D/3D Lead–Tin Perovskite Heterojunctions

Ruggeri, Edoardo; Anaya, Miguel; Gałkowski, Krzysztof; Delport, Géraud; Kosasih, Felix Utama; Abfalterer, Anna; Maćkowski, Sebastian; Ducati, Caterina; Stranks, Samuel D.

doi:10.1002/adma.201905247

Cited by 41 publications

(58 citation statements)

References 78 publications

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“…The small, positive shift in I 3d and N 1s binding energies can possibly indicate hydrogen bond formation between NH 4 + and [PbI 6 ] 4− /[SnI 6 ] 4− moieties. [ 51,52 ] The NH 4 SCN treatment also results in an increase of the I/(Pb + Sn) atomic ratio from 1.97:1 for the pristine perovskite to 2.30:1 for the NH 4 SCN‐treated perovskite films. The NH 4 SCN‐treated perovskite film exhibits a higher photoluminescence intensity than the pristine perovskite (Figure S24, Supporting Information), indicating a reduced nonradiative recombination process.…”

Section: Resultsmentioning

confidence: 99%

Understanding the Film Formation Kinetics of Sequential Deposited Narrow‐Bandgap Pb–Sn Hybrid Perovskite Films

Wang

Datta

et al. 2020

Advanced Energy Materials

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state-of-the-art inorganic photovoltaic (PV) technologies. [4] Developing all-perovskite tandem solar cells with complementary bandgaps is considered as the next step to surpass the Shockley-Queisser efficiency limit for single-junction devices. [5][6][7][8] Solution processability of all components at low-temperature would enhance incentives to explore large-scale implementation of such multi-junction cells. [9] Previous studies [10][11][12] of tandem solar cells have suggested that a combination of a wide-bandgap (1.7 to 1.9 eV) front cell and a narrow-bandgap (0.9 to 1.2 eV) rear cell is ideal for high efficiency multijunctions. Hybrid perovskites AMX 3 , where A is a monovalent cation (formamidinium (FA + ), methylammonium (MA + ) or Cs + ), M is a divalent metal cation (Pb 2+ or Sn 2+ ), and X is a halide anion (I − or Br − ), [13] have a broadly tunable bandgap via compositional engineering. [14] The bandgap of Pb-based perovskites can be continuously tuned from 1.5 to 2.3 eV by substituting I with Br. [15,16] On the other hand, a nonlinear bandgap behavior [17] is observed when alloying Pb (1.5 eV) and Sn-based (1.3 eV) perovskites, providing a minimum bandgap of ≈1.2 eV at 50% to 75% Sncontent. [18][19][20][21] Such mixed Pb-Sn perovskites are considered the most promising narrow-bandgap perovskite materials for tandem devices. [21,22] However, compared to their Pb analogs, Sn-based perovskite precursors have a greater tendency to react and crystallize at room temperature, [23] which makes it difficult to grow compact, smooth, and homogeneous Developing efficient narrow bandgap Pb-Sn hybrid perovskite solar cells with high Sn-content is crucial for perovskite-based tandem devices. Film properties such as crystallinity, morphology, surface roughness, and homogeneity dictate photovoltaic performance. However, compared to Pb-based analogs, controlling the formation of Sn-containing perovskite films is much more challenging. A deeper understanding of the growth mechanisms in Pb-Sn hybrid perovskites is needed to improve power conversion efficiencies. Here, in situ optical spectroscopy is performed during sequential deposition of Pb-Sn hybrid perovskite films and combined with ex situ characterization techniques to reveal the temporal evolution of crystallization in Pb-Sn hybrid perovskite films. Using a twostep deposition method, homogeneous crystallization of mixed Pb-Sn perovskites can be achieved. Solar cells based on the narrow bandgap (1.23 eV) FA 0.66 MA 0.34 Pb 0.5 Sn 0.5 I 3 perovskite absorber exhibit the highest efficiency among mixed Pb-Sn perovskites and feature a relatively low dark carrier density compared to Sn-rich devices. By passivating defect sites on the perovskite surface, the device achieves a power conversion efficiency of 16.1%, which is the highest efficiency reported for sequential solutionprocessed narrow bandgap perovskite solar cells with 50% Sn-content.

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Section: Resultsmentioning

confidence: 99%

Understanding the Film Formation Kinetics of Sequential Deposited Narrow‐Bandgap Pb–Sn Hybrid Perovskite Films

Wang

Datta

et al. 2020

Advanced Energy Materials

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“…Therefore, lead‐free perovskite has become an important research subject. Numerous alternatives with lower toxicity or nontoxicity have been proposed, such as Sn, [ 158 ] Ge, [ 159 ] Sb, [ 160 ] Bi, [ 161 ] Cu, [ 162 ] etc. Among these, Sn‐based perovskite has a narrower optical band gap (≈1 eV) [ 163 ] and higher electron mobility (≈10 2 –10 3 cm 2 V −1 s −1 and Pb‐based perovskite ≈10–10 2 cm 2 V −1 s −1 ) [ 164 ] due to the inactivity of the outer electrons of the tin element.…”

Section: D Perovskite‐based Solar Cellsmentioning

confidence: 99%

Crystallization Kinetics in 2D Perovskite Solar Cells

Wang

Lei

et al. 2020

Advanced Energy Materials

149

124

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volatile decomposition [23] or halide segregation are often observed in hybrid perovskites under various stress conditions (light, [24] thermal, [25] and electric fields [26]); 4) spontaneous phase transition easily occurs for perovskite with unstable crystal structures, particularly for inorganic perovskite. [27-29] To improve the stability of PSCs, researchers attempted numerous methods such as encapsulation, [30] additive engineering, [31] component engineering, [32] etc. [33] However, the PSCs' stability is yet to achieve a perfect solution. Recently, researchers found that the introduction of long-chain organic cations in 3D perovskite as 2D perovskite can block water and oxygen molecules, meanwhile, generate a steric effect to prevent phase transitions, and limit ion migration. [34-36] Hence, fabricating 2D [37,38] or 2D/3D [39-43] mixed perovskite as absorbing layers are effective approaches to improve the stability of PSCs. However, the PCE of 2D PSCs remain lower than that of the 3D ones, which is mainly attributed to the introduction of organic macromolecules that blocks the effective extraction and transport of carriers. [44,45] Fortunately, 2D perovskite usually has three arrangements, namely parallel, perpendicular to the glass substrate or randomly arranged. [46] Manipulating the orientation of the crystal and the phase distribution in the 2D solution-processed perovskite can improve the efficiency and reproducibility of the device. Among them, the most desired arrangement for PSCs is the one that perpendicular to the substrate. Therefore, studying the crystallization kinetics of 2D perovskite is curial to effectively control the film forming process and adjust the crystal orientation (perpendicular to the substrate), which can effectively avoid or reduce the adverse effects of the organic molecular layer and improve device efficiency. [47,48] Nevertheless, few review articles were published on this subject. In this review, we mainly focus on the key issue for controlling crystallization kinetics and summarizing the research progress of their effects on various types of 2D PSCs. We also discuss the crystal/natural quantum well (QW) structure and the original stability for 2D PSCs in detail. Finally, remaining challenges and outlooks are presented. 2. Crystal and Natural Quantum Well Structure The material structure has a substantial impact on performance. [49-51] Properties of 2D and 3D perovskites differ 2D perovskites demonstrate higher moisture stability, oxygen content, thermal stability, and a significantly lower ion migration/phase transition occurrence in comparison to 3D perovskite. These advantages imply huge potential for 2D perovskite in commercial applications in the photovoltaic field. However, the horizontal arrangement of the organic layer severely hinders the transport of carriers, and thus, the power conversion efficiency of 2D perovskite solar cells (PSCs) is significantly lower than that of 3D. Controlling the crystallization orientation to achieve rapid carrier transport can effe...

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“…Therefore the Sn-Pb-based PSCs suffer from lower stability even in an inert atmosphere with a trace amount of oxygen. 18,25,26 The most common strategies to prevent oxidation are incorporating antioxidant additives such as SnF 2 , [26][27][28][29][30] SnBr 2 , 26,27,31 SnCl 2 , 27,32 GuaSCN, 17 ascorbic acid, 33 and sulfonic acid group, 34 applying 2D components as passivation layers, [35][36][37] compositional engineering, 38 as well as utilizing Sn-reduced precursor solutions. 18,39 In addition to the oxygen-induced degradation, other possible degradation mechanisms such as thermal decomposition, 40,41 light-induced degradation, 41,42 and crystal-structure transition 43,44 are less explored for Sn-Pb-based PSCs.…”

Section: Introductionmentioning

confidence: 99%

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

et al. 2020

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Controlling the Growth Kinetics and Optoelectronic Properties of 2D/3D Lead–Tin Perovskite Heterojunctions

Cited by 41 publications

References 78 publications

Understanding the Film Formation Kinetics of Sequential Deposited Narrow‐Bandgap Pb–Sn Hybrid Perovskite Films

Understanding the Film Formation Kinetics of Sequential Deposited Narrow‐Bandgap Pb–Sn Hybrid Perovskite Films

Crystallization Kinetics in 2D Perovskite Solar Cells

Triple-cation low-bandgap perovskite thin-films for high-efficiency four-terminal all-perovskite tandem solar cells

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