In situ preparation of a CsPbBr3/black phosphorus heterostructure with an optimized interface and photodetector application

Detecting Visible to Near-Infrared II Light via CsPbBr3 Nanocrystals/Y6 Heterojunctions

In the endeavor to develop advanced photodetectors (PDs) with superior performance, all-inorganic perovskites, recognized for their outstanding photoelectric properties, have emerged as highly promising materials. Due to their unique electronic structure and band characteristics, the majority of all-inorganic perovskite materials are not sensitive to near-infrared (NIR) light. Here, we demonstrate the fabrication of a high-performance broadband PD comprising CsPbBr3 perovskite NCs/Y6 planar heterojunctions. The incorporation of Y6 not only facilitates charge transfer from CsPbBr3 NCs to Y6 for enhancing photodetection performance under visible illumination but also broadens the absorption spectrum range of the whole device toward the NIR regime. As a result, the heterojunction PD exhibits a photo-to-dark-current ratio above 105, a dynamic range of 149.5 dB, and an impressive lowest detection limit of incident power density of 1.6 nW/cm2 under 505 nm illumination. In the NIR regime, where photon energy is below the bandgap of CsPbBr3, electron-hole pairs can still be produced in the Y6 layer even when illuminated at 1120 nm. Consequently, photodetection is uniquely possible in PDs that incorporate heterojunctions when the illumination wavelength is longer than 565 nm. At 850 nm, the heterojunction device is capable of detecting light with power densities as low as 1.3 μW/cm2 corresponding to a LDR of 99.8 dB. The exceptional performance is attributed to the creation of a heterojunction between CsPbBr3 NCs and Y6. These findings propose a novel approach for developing broadband PDs based on perovskite NC materials.

Advances in Heterostructures for Optoelectronic Devices: Materials, Properties, Conduction Mechanisms, Device Applications

Atomically thin 2D transition metal dichalcogenides (TMDs) have recently been spotlighted for next-generation electronic and photoelectric device applications. TMD materials with high carrier mobility have superior electronic properties different from bulk semiconductor materials. 0D quantum dots (QDs) possess the ability to tune their bandgap by composition, diameter, and morphology, which allows for a control of their light absorbance and emission wavelength. However, QDs exhibit a low charge carrier mobility and the presence of surface trap states, making it difficult to apply them to electronic and optoelectronic devices. Accordingly, 0D/2D hybrid structures are considered as functional materials with complementary advantages that may not be realized with a single component. Such advantages allow them to be used as both transport and active layers in next-generation optoelectronic applications such as photodetectors, image sensors, solar cells, and light-emitting diodes. Here, recent discoveries related to multicomponent hybrid materials are highlighted. Research trends in electronic and optoelectronic devices based on hybrid heterogeneous materials are also introduced and the issues to be solved from the perspective of the materials and devices are discussed.

Surface and Interface Engineering for Highly Stable CsPbBr3/ZnS Core/Shell Nanocrystals

Shelling with chalcogenides on the surface of lead halide perovskite (LHP) nanocrystals (NCs) is believed to be an effective approach to increase their stability under high-moisture/aqueous conditions, which is important for LHP NC-based optoelectronic devices. However, it is still a challenge to prepare high-quality LHP/chalcogenide core/shell NCs with moisture/aqueous stability. In this work, a surface-defect-induced strategy is carried out to facilitate the adsorption of Br- ions and subsequently Zn2+ ions to preform a bipolar surface, which reduces the energy barrier at the CsPbBr3/ZnS interface and promotes the epitaxial growth of the ZnS shell layer. The aqueous stability of the as-received NCs shows an increase of over 12 times compared to that of the original one. Likewise, Mn2+ ions are introduced to further reduce the geometric symmetry mismatch and defect density at the CsPbBr3/ZnS interface. Interestingly, aqueous stability characterizations illustrate negligible degradation even after 230 min of ultrasonication, suggesting their outstanding stability. This work proposes an effective approach to prepare high-quality LHP/chalcogenide core/shell NCs, which possess great potential in the fabrication of stable optoelectronic devices.

Surface polarization-induced emission and stability enhancement of CsPbX3 nanocrystals

Recently, the polarization effect has been receiving tremendous attention, as it can result in improved stability and charge transfer efficiency of metal-halide perovskites (MHPs). However, realizing the polarization effect on CsPbX3 NCs still remains a challenge. Here, metal ions with small radii (such as Mg2+, Li+, Ni2+, etc.) are introduced on the surface of CsPbX3 NCs, which facilitate the arising of electric dipole and surface polarization. The surface polarization effect promotes redistribution of the surface electron density, leading to reinforced surface ligand bonding, reduced surface defects, near unity photoluminescence quantum yields (PLQYs), and enhanced stability. Moreover, further introduction of hydroiodic acid results in the in situ formation of tert-butyl iodide (TBI), which facilitates the successful synthesis of pure iodine-based CsPbI3 NCs with high PLQY (95.3%) and stability under ambient conditions. The results of this work provide sufficient evidence to exhibit the crucial role of the surface polarization effect, which promotes the synthesis of high-quality MHPs and their applications in the fields of optoelectronic devices.

Controlled growth of lead-free cesium zirconium halide double perovskite nanocrystals through a microfluidic reactor

Vacancy-ordered Cs₂ZrX₆ (X = Cl, Br) double perovskite nanocrystals (NCs) have recently attracted increasing attention in optoelectronic applications due to their promising photoluminescence property, high photostability, and low toxicity. However, their ultra-fast reaction limits the growth control and kinetics study of these Cs₂ZrX₆ NCs. Here we report the synthesis of Cs₂ZrX₆ NCs through a microfluidic reactor and achievement of tunable emission wavelengths by controlling the NC size and hybrid halogen ions. Reaction kinetics study reveals that the amine ligand and reaction temperature play dominate roles in the growth and optical performance of the Cs₂ZrX₆ NCs. The effects of flow rate, precursors, and ligand ratio on the morphology and optical property of the NCs were also investigated. This study provides an insight into the growth kinetics of the Cs₂ZrX₆ perovskite NCs and their continuous production through a microfluidic reactor that could facilitate the development and optical application of lead-free vacancy-ordered double perovskite NCs.

Interfacial engineering of halide perovskites and two-dimensional materials

Recently, halide perovskites (HPs) and layered two-dimensional (2D) materials have received significant attention from industry and academia alike. HPs are emerging materials that have exciting photoelectric properties, such as a high absorption coefficient, rapid carrier mobility and high photoluminescence quantum yields, making them excellent candidates for various optoelectronic applications. 2D materials possess confined carrier mobility in 2D planes and are widely employed in nanostructures to achieve interfacial modification. HP/2D material interfaces could potentially reveal unprecedented interfacial properties, including light absorbance with desired spectral overlap, tunable carrier dynamics and modified stability, which may lead to several practical applications. In this review, we attempt to provide a comprehensive perspective on the development of interfacial engineering of HP/2D material interfaces. Specifically, we highlight the recent progress in HP/2D material interfaces considering their architectures, electronic energetics tuning and interfacial properties, discuss the potential applications of these interfaces and analyze the challenges and future research directions of interfacial engineering of HP/2D material interfaces. This review links the fields of HPs and 2D materials through interfacial engineering to provide insights into future innovations and their great potential applications in optoelectronic devices.

Production of high-quality and large lateral-size black phosphorus nanoparticles/nanosheets by liquid-phase exfoliation

The liquid phase exfoliation (LPE) of layered black phosphorus (BP) material is essential in the field of electronics. N-Methyl-2-pyrrolidone (NMP) is one of the most promising precursors for obtaining BP nanosheets/nanoparticles, but the longer sonication time leads to smaller production of phosphorene. Herein, for the first time, the large lateral size fabrication of phosphorene was attained through NMP solvent by optimizing the process parameters. The resultant dispersions were characterized by atomic force microscopy, X-ray powder diffraction, Raman spectroscopy, scanning electron microscopy, transmission electron microscopy, and ultraviolet-visible spectroscopy. The characterization results revealed that the average lateral sizes of BP nanoparticles were found to be 67.8 ± 18.6 nm and the lateral size of fabricated BP nanosheets was found to be 5.37 μm. Moreover, this research provides a strategic approach for the mass production of phosphorene for photodetection applications.

A vertical CsPbBr3/ZnO heterojunction for photo-sensing lights from UV to green band

In this work, we have reported a vertical CsPbBr₃/ZnO heterojunction photodetector for photo-sensing lights from UV to visible band. The ZnO thin film is deposited on the c-sapphire substrate through a molecular beam epitaxy (MBE) technique, and then the CsPbBr₃ thin film is synthesized on the as-prepared ZnO film layer by using a solution processing method. The as-prepared CsPbBr₃/ZnO heterostructure presents type-II energy band structure induced by the energy band offset effect, which can promote the separation and extraction efficiencies of the photo-generated electron-hole pairs. Compared with the CsPbBr₃ based metal-semiconductor-metal (MSM) structure photodetector, the heterojunction photodetector presents higher responsivity and detectivity of 630 µA/W and 7 × 10⁹ Jones. While compared with the ZnO based MSM structure photodetector, the heterojunction device reveals much faster response speeds of 61 µs (rise time) and 1.4 ms (decay time). These findings demonstrate that the CsPbBr₃/ZnO heterojunction photodetector is promising for constructing next generation perovskite based optoelectronic devices.

Tunable Lifetime and Nonlinearity in Two Dimensional Materials Plasmonic-Photonic Absorber

We investigate a framework of local field, quality factor and lifetime for tunable graphene nanoribbon plasmonic-photonic absorbers and study the second order and third order nonlinear optical response of surface plasmons. The energy exchange of plasmonic-photonic absorber occurs in two main ways: one way is the decay process of intrinsic loss for each resonant mode and another is the decay process of energy loss between graphene surface plasmon (GSP) mode and the external light field. The quality factor and lifetime of the plasmonic-photonic absorber can be obtained with using the coupled mode theory (CMT) and finite difference time domain (FDTD) method, which are effectively tunable with changing Fermi energy, carrier mobility and superstrate refractive index. The evolutions of total energy and lifetime of GSP are also shown, which are helpful for the study of micro processes in a two-dimensional material plasmonic-photonic absorber. The strongly localized fundamental field induces a desired increase of second harmonic (SH) wave and third harmonic (TH) wave. The manipulation of the quality factor and lifetime of the GSP makes graphene an excellent platform for tunable two-dimensional material plasmonic-photonic devices to realize the active control of the photoelectric/photothermal energy conversion process and higher harmonic generation.

A Critical Review on Black Phosphorus-Based Photocatalytic CO2 Reduction Application

Energy shortages and greenhouse effects are two unavoidable problems that need to be solved. Photocatalytically converting CO₂ into a series of valuable chemicals is considered to be an effective means of solving the above dilemmas. Among these photocatalysts, the utilization of black phosphorus for CO₂ photocatalytic reduction deserves a lightspot not only for its excellent catalytic activity through different reaction routes, but also on account of the great preponderance of this relatively cheap catalyst. Herein, this review offers a summary of the recent advances in synthesis, structure, properties, and application for CO₂ photocatalytic reduction. In detail, the review starts from the basic principle of CO₂ photocatalytic reduction. In the following section, the synthesis, structure, and properties, as well as CO₂ photocatalytic reduction process of black phosphorus-based photocatalyst are discussed. In addition, some possible influencing factors and reaction mechanism are also summarized. Finally, a summary and the possible future perspectives of black phosphorus-based photocatalyst for CO₂ reduction are established.

Synthesis and stabilization of black phosphorus and phosphorene: recent progress and perspectives

Two-dimensional black phosphorus (BP) has triggered tremendous research interest owing to its unique crystal structure, high carrier mobility, and tunable direct bandgap. Preparation of few-layer BP with high quality and stability is very important for its related research and applications in biomedicine, electronics, and optoelectronics. In this review, the synthesis methods of BP, including the preparation of bulk BP crystal which is an important raw material for preparing few-layer BP, the popular top-down methods, and some direct growth strategies of few-layer BP are comprehensively overviewed. Then chemical ways to enhance the stability of few-layer BP are concretely introduced. Finally, we propose a selection rule of preparation methods of few-layer BP according to the requirement of specific BP properties for different applications. We hope this review would bring some insight for future researches on BP and contributes to the acceleration of BP's commercial progress.

Water-Dispersible CsPbBr3 Perovskite Nanocrystals with Ultra-Stability and its Application in Electrochemical CO2 Reduction

Thanks to the excellent optoelectronic properties, lead halide perovskites (LHPs) have been widely employed in high-performance optoelectronic devices such as solar cells and light-emitting diodes. However, overcoming their poor stability against water has been one of the biggest challenges for most applications. Herein, we report a novel hot-injection method in a Pb-poor environment combined with a well-designed purification process to synthesize water-dispersible CsPbBr₃ nanocrystals (NCs). The as-prepared NCs sustain their superior photoluminescence (91% quantum yield in water) for more than 200 days in an aqueous environment, which is attributed to a passivation effect induced by excess CsBr salts. Thanks to the ultra-stability of these LHP NCs, for the first time, we report a new application of LHP NCs, in which they are applied to electrocatalysis of CO₂ reduction reaction. Noticeably, they show significant electrocatalytic activity (faradaic yield: 32% for CH₄, 40% for CO) and operation stability (> 350 h).

Overcoming barriers in photodynamic therapy harnessing nano-formulation strategies

Photodynamic therapy (PDT) has been extensively investigated for decades for tumor treatment because of its non-invasiveness, spatiotemporal selectivity, lower side-effects, and immune activation ability. It can be a promising treatment modality in several medical fields, including oncology, immunology, urology, dermatology, ophthalmology, cardiology, pneumology, and dentistry. Nevertheless, the clinical application of PDT is largely restricted by the drawbacks of traditional photosensitizers, limited tissue penetrability of light, inefficient induction of tumor cell death, tumor resistance to the therapy, and the severe pain induced by the therapy. Recently, various photosensitizer formulations and therapy strategies have been developed to overcome these barriers. Significantly, the introduction of nanomaterials in PDT, as carriers or photosensitizers, may overcome the drawbacks of traditional photosensitizers. Based on this, nanocomposites excited by various light sources are applied in the PDT of deep-seated tumors. Modulation of cell death pathways with co-delivered reagents promotes PDT induced tumor cell death. Relief of tumor resistance to PDT with combined therapy strategies further promotes tumor inhibition. Also, the optimization of photosensitizer formulations and therapy procedures reduces pain in PDT. Here, a systematic summary of recent advances in the fabrication of photosensitizers and the design of therapy strategies to overcome barriers in PDT is presented. Several aspects important for the clinical application of PDT in cancer treatment are also discussed.

Functionalized Selenium Nanotherapeutics Synergizes With Zoledronic Acid to Suppress Prostate Cancer Cell Growth Through Induction of Mitochondria-Mediated Apoptosis and Cell Cycle S Phase Arrest

The use of established drugs in new therapeutic applications has great potential for the treatment of cancers. Nanomedicine has the advantages of efficient cellular uptake and specific cell targeting. In this study, we investigate using lentinan-functionalized selenium nanoparticles (LET-SeNPs) for the treatment of prostate cancer (PCa). We used assays to demonstrate that a combination of LET-SeNPs and zoledronic acid (ZOL) can reduce PCa cell viability in vitro. Stability and hemocompatibility assays were used to determine the safety of the combination of LET-SeNPs and ZOL. The localization of LET-SeNPs was confirmed using fluorescence microscopy. JC-1 was used to measure the mitochondrial membrane potential, while the cellular uptake, cell cycle and apoptosis were evaluated by flow cytometry. Finally, cell migration and invasion assays were used to evaluate the effects of the combination treatment on cell migration and invasion. Under optimized conditions, we found that LET-SeNPs has good stability. The combination of LET-SeNPs and ZOL can effectively inhibit metastatic PCa cells in a concentration-dependent manner, as evidenced by cytotoxicity testing, flow cytometric analysis, and mitochondria functional test. The enhanced anti-cancer effect of LET-SeNPs and ZOL may be related to the regulation of BCL2 family proteins that could result in the release of cytochrome C from the inner membranes of mitochondria into the cytosol, accompanied by induction of cell cycle arrest at the S phase, leading to irreversible DNA damage and killing of PCa cells. Collectively, the results of this study suggest that the combination of SeNPs and ZOL can successfully inhibit the growth of PCa cells.

Metal Halide Perovskite/2D Material Heterostructures: Syntheses and Applications

The past decade has witnessed the great success achieved by metal halide perovskites (MHPs) in photovoltaic and related fields. However, challenges still remain in further improving their performance, as well as, settling the stability issue for future commercialization. Recently, MHP/2D material heterostructures that combining MHPs with the low-cost and solution-processable 2D materials have demonstrated unprecedented improvement in both performance and stability due to the distinctive features at hetero-interface. The diverse fabrication techniques of MHPs and 2D materials allow them to be assembled as heterostructures with different configurations in a variety of ways. Moreover, the large families of MHPs and 2D materials provide the opportunity for the rational design and modification on compositions and functionalities of MHP/2D materials heterostructures. Herein, a comprehensive review of MHP/2D material heterostructures from syntheses to applications is presented. First, various fabrication techniques for MHP/2D material heterostructures are introduced by classifying them into solid-state methods and solution-processed methods. Then the applications of MHP/2D heterostructures in various fields including photodetectors, solar cells, and photocatalysis are summarized in detail. Finally, current challenges for the development of MHP/2D material heterostructures are highlighted, and future opportunities for the advancements in this research field are also provided.

Coordination-Driven Enhancement of Radiosensitization by Black Phosphorus via Regulating Tumor Metabolism

Coordination-driven surface modification is an effective strategy to achieve nanosystem functionalization and improved physicochemical performance. Black phosphorus (BP)-based nanomaterials demonstrate great potential in cancer therapy, but their poor stability, low X-ray mass attenuation coefficient, and nonselectivity limit the application in radiotherapy. Herein, we used unsaturated iridium complex to coordinate with BP nanosheets to synthesize a two-dimensional layered nanosystem (RGD-Ir@BP) with higher biostability. Ir complex improves the photoelectric properties and photoinduced charge carrier dynamics of BP, hence Ir@BP generated more singlet oxygen after X-ray irradiation. In in vivo experiments, with X-ray irradiation, RGD-Ir@BP effectively inhibited nasopharyngeal carcinoma tumor growth but with minor side effects. Additionally, based on untargeted metabolomics analysis, the combined treatment specifically down-regulated the tumor proliferative mark of prostaglandin E2 in cancer cells. In general, this study provides a design strategy of high-performance coordination-driven BP-based nanosensitizer in cancer radiotherapy.

Fluorescence-enhanced Cs4 PbBr6 /CsPbBr3 composites films synthesized by double-films solid phase reaction method

Due to indispensable ligands, polluted organic solution, or complex vapour deposition, stable CsPbBr₃ film is hard to be prepared directly using a simple and environmentally friendly method. To improve the stability of CsPbBr₃ film and its synthesis methods, the double-films solid phase reaction was developed, and Cs₄ PbBr₆ /CsPbBr₃ composites were designed. Although the synthesized particle had a size of 2-5 μm, much larger than that of quantum dots, in ambient conditions the composites films still showed good photoluminescence properties, with the highest photoluminescence quantum yield of 80%. It had good stability against air, temperature and humidity, and even had interesting fluorescence-enhanced phenomenon after about 4 days.

Two-Dimensional Platinum Diselenide: Synthesis, Emerging Applications, and Future Challenges

In recent years, emerging two-dimensional (2D) platinum diselenide (PtSe2) has quickly attracted the attention of the research community due to its novel physical and chemical properties. For the past few years, increasing research achievements on 2D PtSe2 have been reported toward the fundamental science and various potential applications of PtSe2. In this review, the properties and structure characteristics of 2D PtSe2 are discussed at first. Then, the recent advances in synthesis of PtSe2 as well as their applications are reviewed. At last, potential perspectives in exploring the application of 2D PtSe2 are reviewed.

Niobium Carbide MXenes with Broad-Band Nonlinear Optical Response and Ultrafast Carrier Dynamics

Exploring the nonlinear photonics of emerging promising two-dimensional (2D) materials like MXenes will boost the development of broad-band optoelectronic and photonic applications. In this paper, the broad-band nonlinear optical response and the excited-carrier dynamics of an emerging MXene, Nb₂C, are systematically investigated for the wavelength range of visible to the near-infrared band. The obtained nonlinear optical response shows a wavelength and excitation intensity dependence. The imaginary part of the third-order nonlinear optical susceptibility Imχ⁽³⁾ and figure of merit were found to be -1.4 × 10^-10 esu and 7.5 × 10^-12 esu cm, respectively. The interesting nonlinear absorption response inversion properties (e.g., a shift from saturable absorption to two-photon absorption) of Nb₂C nanosheets in the near-infrared promise possible important applications in nonlinear photonics, such as an optical switch. We also demonstrate that the wavelength-dependent relaxation times consist of two different relaxation components, that is, time constants in which one is hundreds of femtoseconds and the other is several picoseconds. Our results indicate promising potential in near-infrared nanophotonic applications of 2D Nb₂C and offer a promising candidate for 2D-material-based nanophotonic devices and beyond.

First-principles study on photovoltaic properties of 2D Cs2PbI4-black phosphorus heterojunctions

Both 2D perovskite Cs₂PbI₄ and phosphorus are significant optoelectronic semiconductor materials, the optical-electrical characters between both contact interfaces are interesting topics. In present work, we demonstrate comparative investigation of optoelectronic properties for two kinds of electrical contact interfaces. i.e. Pb-I and Cs-I interfaces with black phosphorus contacts. The carrier transport, charge transferring and optical properties for both cases are investigated by using first principle calculation. Both contact interfaces exhibit type II band alignment with direct band gap. Charge carrier migration from Cs-I interface to black phosphorus is more strong than that of Pb-I interface by considering differential charge density and bader charge between distinct electrical contact interfaces. Besides, electron-hole effective masses of heterojunctions for both cases along different direction are investigated. Optical absorption coefficients of both cases are compared with those of free-standing Cs₂PbI₄ and black phosphorus in the visible spectrum. We systematically compared advantages and disadvantages of two kinds of contact interfaces for photovoltaic application, and the results reveal interfacial engineering of 2D heterojunction plays a important role in tuning optoelectronic properties.

Improvement in quantum yield by suppression of trions in room temperature synthesized CsPbBr3 perovskite quantum dots for backlight displays

Surface defects and synthesis methods play important roles in the photoluminescence quantum yield (PLQY), stability, and the device performance of lead halide perovskite quantum dots (PQDs). In this study, we report a quadruple-ligand (tri-n-octylphosphine, didodecyldimethylammonium bromide, tetraoctylammonium bromide, and oleic acid) assisted room-temperature method for synthesizing CsPbBr₃ QDs (RT-CsPbBr₃) with an absolute PLQY of 83%. X-ray photoelectron spectroscopy confirms the high completeness of the Pb-Br octahedron through the absence of lead ions and presence of more bromide ions on the surface of RT-CsPbBr₃ QDs. The exciton dynamics of RT-CsPbBr₃ QDs is studied by using femtosecond transient absorption, time-resolved PL, and single-dot spectroscopy, which provide strong evidence of the suppression of trion formation compared with the hot injection-synthesized CsPbBr₃ (HI-CsPbBr₃) QDs. The white light-emitting diode (LED) fabricated with RT-CsPbBr₃ PQDs and a K₂SiF₆:Mn⁴⁺ phosphor for backlight applications achieved a wide color gamut of 124% of the National Television System Committee (NTSC) standard.

Enhanced Photocurrent Owing to Shuttling of Charge Carriers across 4-Aminothiophenol-Functionalized MoSe2-CsPbBr3 Nanohybrids

Mixed-dimensional van der Waals nanohybrids (MvNHs) of two-dimensional transition-metal dichalcogenides (TMDs) and zero-dimensional perovskites are highly promising candidates for high-performance photonic device applications. However, the growth of perovskites over the surface of TMDs has been a challenging task due to the distinguishable surface chemistry of these two different classes of materials. Here, we demonstrate a synthetic route for the design of MoSe₂-CsPbBr₃ MvNHs using a bifunctional ligand, i.e., 4-aminothiophenol. Close contact between these two materials is established via a bridge that leads to the formation of a donor-bridge-acceptor system. The presence of the small conjugated ligand facilitates faster charge diffusion across MoSe₂-CsPbBr₃ interfaces. Density functional theory calculations confirm the type-II band alignment of the constituents within the MvNHs. The MoSe₂-CsPbBr₃ nanohybrids show much higher photocurrent (∼2 × 10⁴-fold photo-to-dark current ratio) as compared to both pure CsPbBr₃ nanocrystals and pristine MoSe₂ nanosheets owing to the synergistic effect of pronounced light-matter interactions followed by efficient charge separation and transportation. This study suggests the use of a bifunctional ligand to construct a nanohybrid system to tune the optoelectronic properties for potential applications in photovoltaic devices.

High Efficiency Mesoscopic Solar Cells Using CsPbI3 Perovskite Quantum Dots Enabled by Chemical Interface Engineering

All-inorganic α-CsPbI₃ perovskite quantum dots (QDs) are attracting great interest as solar cell absorbers due to their appealing light harvesting properties and enhanced stability due to the absence of volatile organic constituents. Moreover, ex situ synthesized QDs significantly reduce the variability of the perovskite layer deposition process. However, the incorporation of α-CsPbI₃ QDs into mesoporous TiO₂ (m-TiO₂) is highly challenging, but these constitute the best performing electron transport materials in state-of-the-art perovskite solar cells. Herein, the m-TiO₂ surface is engineered using an electron-rich cesium-ion containing methyl acetate solution. As one effect of this treatment, the solid-liquid interfacial tension at the TiO₂ surface is reduced and the wettability is improved, facilitating the migration of the QDs into m-TiO₂. As a second effect, Cs⁺ ions passivate the QD surface and promote the charge transfer at the m-TiO₂/QD interface, leading to an enhancement of the electron injection rate by a factor of 3. In combination with an ethanol-environment smoothing route that significantly reduces the surface roughness of the m-TiO₂/QD layer, optimized devices exhibit highly reproducible power conversion efficiencies exceeding 13%. The best cell with an efficiency of 14.32% (reverse scan) reaches a short-circuit current density of 17.77 mA cm^-2, which is an outstanding value for QD-based perovskite solar cells.