Divalent Anionic Doping in Perovskite Solar Cells for Enhanced Chemical Stability

SnO2 Interacted with Sodium Thiosulfate for Perovskite Solar Cells over 25% Efficiency

Tin oxide (SnO2) as electron transportation layer (ETL) has demonstrated remarkable performance applied in perovskite solar cells but still accommodated a host of defects such as oxygen vacancies, uncoordinated Sn4+ , and absorbed hydroxyl groups. Here, we use inorganic sodium thiosulfate Na2S2O3 to modify SnO2 nanoparticles in a bulk blending manner. Strong interaction between Na2S2O3 and SnO2 occurs, as reflected from the elemental chemical state change. The interaction has endowed the SnO2 film with better uniformity, increased conductivity, and more matched energy level with perovskite. Moreover, the modified SnO2 film as a substrate could promote the crystallization of perovskite by suppressing unreacted residual PbI2. The trap density from perovskite bulk to the SnO2 film across their interface has been effectively reduced, thus inhibiting the nonradiative recombination and promoting the transportation and extraction of charge carriers. Finally, the solar cell based on modified SnO2 has achieved a champion efficiency of 25.2%, demonstrating the effectiveness and potential of sulfur-containing molecules on optimizing the SnO2 property.

Inhibition of Ion Migration for Highly Efficient and Stable Perovskite Solar Cells

In recent years, organic-inorganic halide perovskites are now emerging as the most attractive alternatives for next-generation photovoltaic devices, due to their excellent optoelectronic characteristics and low manufacturing cost. However, the resultant perovskite solar cells (PVSCs) are intrinsically unstable owing to ion migration, which severely impedes performance enhancement, even with device encapsulation. There is no doubt that the investigation of ion migration and the summarization of recent advances in inhibition strategies are necessary to develop "state-of-the-art" PVSCs with high intrinsic stability for accelerated commercialization. This review systematically elaborates on the generation and fundamental mechanisms of ion migration in PVSCs, the impact of ion migration on hysteresis, phase segregation, and operational stability, and the characterizations for ion migration in PVSCs. Then, many related works on the strategies for inhibiting ion migration toward highly efficient and stable PVSCs are summarized. Finally, the perspectives on the current obstacles and prospective strategies for inhibition of ion migration in PVSCs to boost operational stability and meet all of the requirements for commercialization success are summarized.

Extrinsic Interstitial Ions in Metal Halide Perovskites: A Review

Perovskite solar cells have rapidly developed as a promising technology for the next generation of low-cost photovoltaics, receiving enormous attention from researchers and industries. Compared to traditional semiconducting materials, metal halide perovskite exhibits outstanding tolerance to extrinsic ions. At a certain range of doping concentration, the interstitial occupancy of extrinsic ions provides appealing benefits to the perovskite films, contributing to higher performance and stability of the devices. This review summarizes the research progress of interstitial ions for metal halide perovskite, providing insights into the mechanism and identification of interstitial doping of extrinsic ions, covering the benefits of interstitial ions in regulating crystal growth, inhibiting ion migration, and reducing defect density. Finally, based on the latest progress and findings, further topics and directions of research on interstitial ions in metal halide perovskite are proposed to advance the understanding of interstitial ions in perovskite and promote the development of perovskite photovoltaic technology.

Multiple-ion Management of Perovskites by Regulating Spatial Distribution of Hydroxyls in Oligosaccharides

Suppressing migrations of intrinsic and extrinsic ions (e.g., Pb2+ , I- , FA+ /MA+ , and Li+ ) in organic-inorganic hybrid perovskites is critical for alleviating the hysteresis and degradation of perovskite solar cells (PSCs). However, various additives reported for that purpose usually interact with one or two types of those ions, not inhibiting multiple-ion migrations simultaneously. Two oligosaccharides (β-cyclodextrin (β-CD) and maltotetraose (G4)), containing 14 hydroxyls (-OH) with different spatial distributions, for the suppression of multiple-ion migrations in PSCs is herein employed. Compared to linear arrangement of -OH in G4, annular distribution of -OH around wide and narrow rims of β-CD can form supramolecular multi-site interactions in a focal manner with various ions, more effectively capturing and immobilizing these migrated ions. With this multiple-ion management strategy, β-CD-based PSCs exhibit an impressive efficiency of 24.22% with negligible hysteresis and excellent device stability. This work highlights the significances of multi-site interactions and molecular configuration of the additive for inhibiting multi-ion migrations in PSCs.

Emerging Halide Perovskite Ferroelectrics

Halide perovskites have gained tremendous attention in the past decade owing to their excellent properties in optoelectronics. Recently, a fascinating property, ferroelectricity, has been discovered in halide perovskites and quickly attracted widespread interest. Compared with traditional perovskite oxide ferroelectrics, halide perovskites display natural advantages such as structural softness, low weight, and easy processing, which are highly desirable in applications pursuing miniaturization and flexibility. This review focuses on the current research progress in halide perovskite ferroelectrics, encompassing the emerging materials systems and their potential applications in ferroelectric photovoltaics, self-powered photodetection, and X-ray detection. The main challenges and possible solutions in the future development of halide perovskite ferroelectric materials are also attempted to be pointed out.

Nanoscale Encapsulation of Hybrid Perovskites Using Hybrid Atomic Layer Deposition

Organic-inorganic hybrid perovskites have shown tremendous potential for optoelectronic applications. Ion migration within the crystal and across heterointerfaces, however, imposed severe problems with material degradation and performance loss in devices. Encapsulating hybrid perovskite with a thin physical barrier can be essential for suppressing the undesirable interfacial reactions without inhibiting the desirable transport of charge carriers. Here, we demonstrated that nanoscale, pinhole-free Al₂O₃ layer can be coated directly on the perovskite CH₃NH₃PbI₃ using atomic layer deposition (ALD). The success can be attributed to a multitude of strategies including surface molecular modification and hybrid ALD processing combining the thermal and plasma-enhanced modes. The Al₂O₃ films provided remarkable protection to the underlying perovskite films, surviving by hours in solvents without noticeable decays in either structural or optical properties. The results advanced the understanding of applying ALD directly on hybrid perovskite and provided new opportunities to implement stable and high-performance devices based on the perovskites.

Doping Induced Orbit-Orbit Interaction between Excitons While Enhancing Photovoltaic Performance in Tin Perovskite Solar Cells

Doping has been used as a common method to improve photovoltaic performance in perovskite solar cells (PSCs). This paper reports a new phenomenon that the SnF₂ doping can largely increase the exciton-exciton interaction through orbital magnetic dipoles toward increasing dissociation probabilities in lead-free FASnI₂Br PSCs. Essentially, when orbit-orbit interaction between excitons occurs, linearly and circularly polarized photoexcitations can inevitably generate different photocurrents, giving rise to a ΔJ_sc phenomenon. Here, it is found that, when SnF₂ doping is used to boost photovoltaic efficiency to 7.61%, the orbit-orbit interaction is increased by a factor of 2.2, shown as the ΔJ_sc changed from 1.21% to 0.55%. Simultaneously, magnetic field effects of J_sc indicate that increasing orbit-orbit interaction leads to an increase on the spin-orbital coupling in Sn perovskites (FASnI₂Br) upon SnF₂ doping. This presents a new doping effect occurring in the Sn perovskite solar cell toward enhancing photovoltaic efficiency.

Enhancement of Photoluminescence Quantum Yield and Stability in CsPbBr3 Perovskite Quantum Dots by Trivalent Doping

We determine the influence of substitutional defects on perovskite quantum dots through experimental and theoretical investigations. Substitutional defects were introduced by trivalent dopants (In, Sb, and Bi) in CsPbBr3 by ligand-assisted reprecipitation. We show that the photoluminescence (PL) emission peak shifts toward shorter wavelengths when doping concentrations are increased. Trivalent metal-doped CsPbBr3 enhanced the PL quantum yield (~10%) and air stability (over 10 days). Our findings provide new insights into the influence of substitutional defects on substituted CsPbBr3 that underpin their physical properties.

Defect Passivation in Hybrid Perovskite Solar Cells by Tailoring the Electron Density Distribution in Passivation Molecules

Commercialization of perovskite solar cells (PSCs) requires developing high-efficiency devices with good stability. Ionic defects existing in the perovskite layer can serve as nonradiative recombination centers to deteriorate the performance of PSCs and can introduce chemical degradation of the perovskite material introducing instability issues. Here, passivation molecules with various electron density distributions (EDD) are employed as an ideal model to reveal the role of EDD on defect passivation in perovskite thin films. Power conversion efficiency (PCE) exceeding 21% with good stability in humid air was obtained for planar PSCs with the 4-aminobenzonitrile (ABN) additive, higher than the reference PSCs with a PCE of 20.22%. The improved stability and performance features are attributed to the efficient passivation for charged defects in perovskites by adding ABN, which guarantees a smaller Urbach energy, longer carrier lifetime, and less traps in the perovskite films.

Hybrid Organic-Inorganic Perovskites as Promising Substrates for Pt Single-Atom Catalysts

Single-atom catalysts (SACs) combine the best of two worlds by bridging heterogeneous and homogeneous catalysis. The superior catalytic properties of SACs, however, can hardly be exploited without a suitable substrate. Here, we explore the possibility of using hybrid organic-inorganic perovskites as supporting materials for single transition-metal atoms. By means of first-principles calculations, we predict that single Pt atoms can be incorporated into methylammonium lead iodide surfaces by replacing the methylammonium groups at the outermost layer. The iodide anions at the surface provide potentially uniform anchoring sites for the Pt atoms and donate electrons, generating negatively charged Pt_{1}^{δ-} species that allow for preferential O_{2} adsorption in the presence of CO. Such Pt sites are able to catalyze CO oxidation and may also play a role in CO_{2} reduction. The fundamental understanding generated here will shed light on potential applications of hybrid perovskites in the field of (photo)catalysis.

Interfacial Sulfur Functionalization Anchoring SnO2 and CH3 NH3 PbI3 for Enhanced Stability and Trap Passivation in Perovskite Solar Cells

Trap states at the interface or in bulk perovskite materials critically influence perovskite solar cells performance and long-term stability. Here, a strategy for efficiently passivating charge traps and mitigating interfacial recombination by SnO₂ surface sulfur functionalization is reported, which utilizes xanthate decomposition on the SnO₂ surface at low temperature. The results show that functionalized sulfur atoms can coordinate with under-coordinated Pb²⁺ ions near the interface. After device fabrication under more than 60 % humidity in ambient air, the efficiency of methylammonium lead iodide (MAPbI₃ ) perovskite solar cells based on sulfur-functionalized SnO₂ increased from 16.56 % to 18.41 % with suppressed hysteresis, which resulted from the accelerated interfacial charge transport kinetics and decreased traps in bulk perovskite by interfacial sulfur functionalization. Additionally, thermally stimulated current studies show the decreased trap density in the shallow trap area after interfacial sulfur functionalization. The interfacial sulfur functionalized solar cells without sealing also exhibited considerable retardation of solar cell degradation with only 10 % degradation after 70 days air storage. This work demonstrates a facile sulfur functionalization strategy by using xanthate decomposition on SnO₂ surfaces to obtain highly efficient perovskite solar cells.

Wavelength-Tunable and Highly Stable Perovskite-Quantum-Dot-Doped Lasers with Liquid Crystal Lasing Cavities

This study applies a low-cost solvothermal method to synthesize all-inorganic (lead-free cesium tin halide) perovskite quantum dots (AIPQDs) and to fabricate AIPQD-doped lasers with cholesteric liquid crystal (CLC) lasing cavities. The lasers present highly qualified lasing features of low threshold (150 nJ/pulse) and narrow line width (0.20 nm) that are attributed to the conjunction of the suppression of photoluminescence (PL) loss caused by the quantum confinement of AIPQDs and the amplification of PL caused by the band-edge effect of the CLC-distributed feedback resonator. In addition, the lasers possess highly flexible lasing-wavelength tuning features and a long-term stability under storage at room temperature and under high humidity given the protective role of CLC. These advantages are difficult to confer to typical light-emitting perovskite devices. Given these merits, the AIPQD-doped CLC laser device has considerable potential applications in optoelectronic and photonic devices, including lighting, displays, and lasers.