A-site tailoring in the vacancy-ordered double perovskite semiconductor Cs2SnI6 for photovoltaic application
Graphical abstract
Introduction
The lead-free halide derivatives-based absorber materials have been gained much attention as alternatives [[1], [2], [3]] [[1], [2], [3]] [[1], [2], [3]] to address the toxicity and stability issues of lead halide perovskite-based solar cells (Pb-HaPSCs) [[4], [5], [6]]. To avoid the toxicity of Pb, the tin-based halide materials are widely being explored due to their favorably optoelectronic properties and non-toxicity [7,8]. Though Sn is isoelectronic with Pb, the intrinsic instability of Sn2+ is deleterious for degradation of Sn-perovskite film resulting in poor device stability [[9], [10], [11]]. On the other hand, despite having excellent film stability of the Bi-based halide derivatives [[12], [13], [14], [15]], [[12], [13], [14], [15]] [[12], [13], [14], [15]] the higher bandgap energies (Eg1.8 eV) of these materials limit for device applications.
Among the suitable alternatives, the vacancy-ordered double perovskite (A2BX6), a family of halide perovskite derivatives has drawn attention as a Pb-free candidate for application in solar cell devices [[16], [17], [18], [19], [20]]. The A2BX6 perovskites show several similarities to ABX3. Although the structure is formed by a face-centered lattice of isolated [BX6] octahedral units connected by A-site cations, the closed-packed anionic lattice retains as in ABX3 perovskites. Many theoretical and experimental works have been reported getting insight into the structural, optical, electronic, and intrinsic defect properties of A2BX6 derivatives. Currently, Cs2SnI6 derivatives have drawn attention due to an optimal bandgap of (1.2–1.6 eV) and optoelectronic properties [18,21,22]. Since the Sn atom in Cs2SnI6 consists of the stable +4 oxidation state, it is an excellent alternative to address the toxicity and stability issue of Pb-HaPSCs. Therefore, this material has been investigated for solar cell devices [[23], [24], [25]] as well as other applications such as; photodetectors [26] photocatalysts [27], and photoelectrochemical water splitting [28]. Kanatzidis and co-workers have firstly reported the regular device structure with Cs2SnI6 films by thermal annealing of the stack of SnI2 and CsI in the air resulting in 1% power conversion efficiency (PCE) [18]. Cao and co-workers also reported mesoscopic Cs2SnI6 based solar cells using different nanostructured ZnO nanorods as ETLs showing device efficiency of ~1% [29]. Few reports also have documented the film preparation by various methods. The Cs2SnI6 films also have been prepared by a hybrid deposition approach followed by vapor-assisted post-annealing [30,31]. The Cs2SnI6 films with mixed halides prepared by spraying the molecular precursor in ambient air have demonstrated a tunable bandgap energy (1.5–3.1 eV) and thermal stability [21,22,32]. Deng and co-workers have reported Cs2SnI6 nanocrystals [33]. They have demonstrated various shapes (from spherical quantum dots, nanorods, nanowires, nanobelts to nanoplates) using a facile hot-injection process. The nanocrystals of double perovskites have been reported with excellent and stable optical emission properties [34]. Recently, Grigorieva and co-workers have reported trivalent doping with In+3 in Cs2SnI6 prepared by solid-phase ampoule synthesis showing higher carrier concentration [35]. The reports mentioned above have documented the effect on opto-physical properties, structural regulation, and film quality under various fabrication processes and composition engineering. In theoretical aspects, Neilson and co-workers have documented that the substitution of Sn by Te in Cs2SnI6 structure leads to defect intolerance [16] as well as reduces electrical conductivity accompanied by an increase in the degree of anharmonicity [36]. Moreover, the A-site i.e. Cs substitution by organic cations; methylammonium (MA) and formamidinium (FA) in Cs2SnI6 structure has revealed the increase in anharmonic lattice dynamics with a reduction in electrical conductivity through a decrease in carrier concentration and carrier mobilities [17]. Similarly, Rb substitution demonstrates the octahedral tilting and stronger electron-phonon interactions [37]. Thus, these theoretical studies suggest that the substitution of A or B- sites affects the structural and transport properties of Cs2SnI6 that can be engineering by tailoring the additive composition. However, there are still lacking systematic studies on this class of materials. Therefore, it demands several experimental studies to get insight into material properties and device applications.
In this work, we have investigated the effect of substitution of Cs+ by smaller cations; Rb+ and Ag+ in Cs2SnI6 materials in film quality, device performance, and optoelectronic properties. The (Cs1-xAx)2SnI6 perovskite (where A = Rb+, Ag+) films prepared by spray pyrolysis deposition in ambient air show a compact and uniform morphology compared to pristine. We have studied the structural, optical, and optoelectronic properties of the fabricated films focusing on photovoltaic application. Our results suggest that the partial substitution of A-site improves optoelectronic properties of (Cs1-xAx)2SnI6 but secondary phases grow with a higher percentage of A-site substitution. Thus, the preliminary device results using A-site engineered Cs2-xAxSnI6 film demonstrated improvement in device parameters with promising VOC (~0.378 V). The capacitance analysis demonstrated the bulk and interface defect in the range of 1019 to 1022 cm−3 that is a dominant factor for the poor device performance. Our work underscores a new approach for the development of air-stable Pb free halide perovskite by tailoring the crystal lattice and interface layer.
Section snippets
Results and discussion
We prepared all inorganic Pb-free vacancy-ordered double perovskite with A-site engineered (Cs1-xAx)2SnI6 (where A = Rb+ and Ag+) (x = 0–1) crystal as described in the experimental section by spray pyrolysis deposition technique as depicted in Fig. S1 (supporting information). Note that the film deposition was carried out in ambient air. The photograph of films prepared by varying the content of Rb and Ag in Cs2SnI6 precursor solution are depicted in supporting information Fig. S2. It shows a
Conclusions
In this report, we have prepared air-stable caesium tin iodide (Cs2SnI6) double perovskite with A-site additive using molecular precursor and deposited by homemade spray pyrolysis technique. The (Cs1-xAx)2SnI6 films with A-site tailoring (Rb, Ag) have been investigated to understand the film growth properties (morphology, structural properties, opto-physical properties). The Cs2SnI6 films demonstrate comparatively compact and uniform morphology by incorporating the additives. The XRD analysis
Author contribution
Shodruz T. Umedov: Methodology, Formal analysis, Writing – original draft. Dhruba B. Khadka: Conceptualization, Methodology, Formal analysis, Writing – original draft, Writing – review & editing. Masatoshi Yanagida: Project administration, Writing – review & editing. Anastasia Grigorieva: Supervision, Writing – review & editing. Yasuhiro Shirai: Supervision, Methodology, Writing – review & editing.
CRediT authorship contribution statement
Shodruz T. Umedov: Methodology, Formal analysis, Writing – original draft. Dhruba B. Khadka: Conceptualization, Methodology, Formal analysis, Writing – original draft, Writing – review & editing. Masatoshi Yanagida: Project administration, Writing – review & editing. Anastasia Grigorieva: Supervision, Writing – review & editing. Yasuhiro Shirai: Supervision, Methodology, Writing – review & editing.
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
D. B. K. acknowledges the support by The Hitachi Global Foundation, Kurata Grant (#1391), Japan. S.T.U. and A. G. thank the National Institute for Materials Science (NIMS), Japan and Lomonosov Moscow State University, Russia, for the International Cooperative Graduate Program (ICGP) fellowship.
References (49)
- et al.
From unstable CsSnI3 to air-stable Cs2SnI6: a lead-free perovskite solar cell light absorber with bandgap of 1.48 eV and high absorption coefficient
Sol. Energy Mater. Sol. Cells
(2017) - et al.
Revealing the structural, electronic and optical properties of lead-free perovskite derivatives of Rb2SnX6(X = Cl, Br and I): a theory calculation
Sol. Energy
(2019) - et al.
Solar cell using spray casted Cs2SnI6 perovskite thin films on chemical bath deposited CdS yielding high open circuit voltage
Sol. Energy
(2020) - et al.
Synthesis of perovskite Cs2SnI6 film via the solution processed approach: first study on the photoelectrochemical water splitting application
J. Alloys Compd.
(2019) - et al.
Single step deposition of Cs2SnIxCl6-x thin films with uniform morphology, composition and high air stability
Mater. Sci. Semicond. Process.
(2020) - et al.
Ammoniated aqueous precursor ink processed copper iodide as hole transport layer for inverted planar perovskite solar cells
Sol. Energy Mater. Sol. Cells
(2020) - et al.
SnS nanosheet films deposited via thermal evaporation: the effects of buffer layers on photovoltaic performance
Sol. Energy Mater. Sol. Cells
(2016) - et al.
Lead-free solid-state organic-inorganic halide perovskite solar cells
Nat. Photonics
(2014) - et al.
“Unleaded” perovskites: status quo and future prospects of tin-based perovskite solar cells
Adv. Mater.
(2019) - et al.
Reducing trap density and carrier concentration by a Ge additive for an efficient quasi 2D/3D perovskite solar cell
J. Mater. Chem. A.
(2020)
One-Year stable perovskite solar cells by 2D/3D interface engineering
Nat. Commun.
Halide perovskite photovoltaics: background, status, and future prospects
Chem. Rev.
Degradation of encapsulated perovskite solar cells driven by deep trap states and interfacial deterioration
J. Mater. Chem. C.
Lead-free organic-inorganic tin halide perovskites for photovoltaic applications
Energy Environ. Sci.
Stabilizing halide perovskite surfaces for solar cell operation with wide-bandgap lead oxysalts
Science
Highly reproducible Sn-based hybrid perovskite solar cells with 9% efficiency
Adv. Energy Mater.
Attenuating the defect activities with a rubidium additive for efficient and stable Sn-based halide perovskite solar cells
J. Mater. Chem. C.
Strategies to improve performance and stability for tin-based perovskite solar cells
ACS Energy Lett
Research Update: bismuth based materials for photovoltaics
Apl. Mater.
Silver bismuth sulfoiodide solar cells: tuning optoelectronic properties by sulfide modification for enhanced photovoltaic performance
Adv. Energy Mater.
Tailoring the film morphology and interface band offset of caesium bismuth iodide-based Pb-free perovskite solar cells
J. Mater. Chem. C.
Effect of solvent vapour annealing on bismuth triiodide film for photovoltaic applications and its optoelectronic properties
J. Mater. Chem. C.
Defect tolerance to intolerance in the vacancy-ordered double perovskite semiconductors Cs2SnI6 and Cs2TeI6
J. Am. Chem. Soc.
Anharmonicity and octahedral tilting in hybrid vacancy-ordered double perovskites
Chem. Mater.
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