Metallic surface doping of metal halide perovskites

Electrical Doping Regulation of Carrier Recombination Enhances the Perovskite Solar Cell Efficiency beyond 28

With the power conversion efficiency (PCE) of perovskite solar cells (PSCs) exceeding 26.7%, achieving further enhancements in device performance has become a key research focus. Here, we investigate the impact of electrical doping in the perovskite layer using the drift-diffusion equation-based device physics model, coupled with a self-developed equivalent circuit model. Our results demonstrate that electrical doping can increase the PCE from 24.78% to >28%. In-depth theoretical analysis reveals that these improvements in performance are driven by the modulation of carrier recombination processes through doping, leading to significant increases in the open-circuit voltage and fill factor. Additionally, we explore the influence of physical parameters on device performance. Our study identifies an optimal doping concentration range from 1.0 × 1017 to 1.0 × 1019 cm-3 and a transport layer mobility of >0.01 cm2 V-1 s-1. This work provides a theoretical foundation for the development of ultra-high-performance PSCs through targeted electrical doping strategies.

Footprints of scanning probe microscopy on halide perovskites

Scanning probe microscopy (SPM) and advanced atomic force microscopy (AFM++) have become pivotal for nanoscale elucidation of the structural, optoelectronic and photovoltaic properties of halide perovskite single crystals and polycrystalline films, both under ex situ and in situ conditions. These techniques reveal detailed information about film topography, compositional mapping, charge distribution, near-field electrical behaviors, cation-lattice interactions, ion dynamics, piezoelectric characteristics, mechanical durability, thermal conductivity, and magnetic properties of doped perovskite lattices. This article outlines the advancements in SPM techniques that deepen our understanding of the optoelectronic and photovoltaic performances of halide perovskites.

Achieving Super-Metallophobicity on Silicon-based Ceramics at High Temperature

As a critical concept in physical chemistry, superwettability is widely concerned in both fundamental science and practical engineering in past few decades. Despite this, investigation on high temperature superwettability is still a void, which is significant both in scientific and industrial fields. Herein, a ceramic with specific high temperature non-wetting property, Si2N2O is proposed. Compared with other materials, Si2N2O is elucidated with better practical non-wetting property against various non-ferrous metals. Combining with micro-nanostructures, the metallophobicity is further improved (contact angle >150° and contact angle hysteresis ≈0°). The extraordinary metal repellency is defined as "super-metallophobicity", which is proved to be induced by distinctive thermodynamic and dynamic wetting behavior on the rough surface. The research of super-metallophobicity not only sheds light on superwettability at high temperature, but also offers worthy insights for future potential material design in a wide range of applications, such as metallurgy, 3D printing and semiconductor industry.

Inhibiting Ion Migration and Stabilizing Crystal-Phase in Halide Perovskite via Directly Incorporated Fluoride Anion

Fluoride anion (F-) with extremely high electronegativity has been under intensive investigation in perovskite solar cells due to its remarkable defect suppression and great improvement of device performance. Nevertheless, these researches only focus on the surface, grain boundaries, or interface modification, the direct insertion of F- into the crystal lattice of regular lead halide perovskite films is still unrevealed. Herein, F- was successfully incorporated into the perovskite lattice by overcoming the insolubility of PbF2 via the introduced pyridinium halide as a novel volatile solubilizing ligand. The strong electronegativity of F- can strongly increase the binding energy of all the ions in CsPbI2Br and inhibit their defect formations. A trace amount of F- incorporation not only enhanced the optoelectronic properties but also effectively mitigated the ion migration and phase separation simultaneously. The photovoltaic performance and operational stability of perovskite solar cells were significantly improved with a champion efficiency of 17.78 % (38.01 %) under AM 1.5G (1000 lux indoor light). Moreover, F- can also be directly inserted into the hybrid perovskite lattice and greatly stabilized crystal-phase, enabling efficient fully MA-free FAPbI3 devices with 25.10 % efficiency. Our strategy sheds light on F-containing perovskites and provides a promising way to tackle ion migration and stabilize the crystal phase in halide perovskites.

Precursor-Engineered Volatile Inks Enable Reliable Blade-Coating of Cesium-Formamidinium Perovskites Toward Fully Printed Solar Modules

Reliable fabrication of large-area perovskite films with antisolvent-free printing techniques requires high-volatility solvents, such as 2-methoxyethanol (2ME), to formulate precursor inks. However, the fabrication of high-quality cesium-formamidinium (Cs-FA) perovskites has been hampered using volatile solvents due to their poor coordination with the perovskite precursors. Here, this issue is resolved by re-formulating a 2ME-based Cs0.05FA0.95PbI3 ink using pre-synthesized single crystals as the precursor instead of the conventional mixture of raw powders. The key to obtaining high-quality Cs-FA films lies in the removal of colloidal particles from the ink and hence the suppression of colloid-induced heterogeneous nucleation, which kinetically facilitates the growth of as-formed crystals toward larger grains and improved film crystallinity. Employing the precursor-engineered volatile ink in the vacuum-free, fully printing processing of solar cells (with carbon electrode), a power conversion efficiency (PCE) of 19.3%, a T80 (80% of initial PCE) of 1000 h in ISOS-L-2I (85 °C/1 Sun) aging test and a substantially reduced bill of materials are obtained. The reliable coating methodology ultimately enables the fabrication of carbon-electrode mini solar modules with a stabilized PCE of 16.2% (average 15.6%) representing the record value among the fully printed counterparts and a key milestone toward meeting the objectives for a scalable photovoltaic technology.

Competing Charge Transfer and Screening Effects in Two-Dimensional Ferroelectric Capacitors

Two-dimensional (2D) ferroelectrics promise ultrathin flexible nanoelectronics, typically utilizing a metal-ferroelectric-metal sandwich structure. Electrodes can either contribute free carriers to screen the depolarization field, enhancing nanoscale ferroelectricity, or induce charge doping, disrupting the long-range crystalline order. We explore electrodes' dual roles in 2D ferroelectric capacitors, supported by first-principles calculations covering a range of electrode work functions. Our results reveal volcano-type relationships between ferroelectric-electrode binding affinity and work function, which are further unified by a quadratic scaling between the binding energy and the transferred interfacial charge. At the monolayer limit, charge transfer dictates the ferroelectric stability and switching properties. This general characteristic is confirmed in various 2D ferroelectrics including α-In2Se3, CuInP2S6, and SnTe. As the ferroelectric layer's thickness increases, the capacitor stability evolves from a charge-transfer-dominated state to a screening-dominated state. The delicate interplay between these two effects has important implications for 2D ferroelectric capacitor applications.

Surface heterojunction based on n-type low-dimensional perovskite film for highly efficient perovskite tandem solar cells

Enhancing the quality of junctions is crucial for optimizing carrier extraction and suppressing recombination in semiconductor devices. In recent years, metal halide perovskite has emerged as the most promising next-generation material for optoelectronic devices. However, the construction of high-quality perovskite junctions, as well as characterization and understanding of their carrier polarity and density, remains a challenge. In this study, using combined electrical and spectroscopic characterization techniques, we investigate the doping characteristics of perovskite films by remote molecules, which is corroborated by our theoretical simulations indicating Schottky defects consisting of double ions as effective charge dopants. Through a post-treatment process involving a combination of biammonium and monoammonium molecules, we create a surface layer of n-type low-dimensional perovskite. This surface layer forms a heterojunction with the underlying 3D perovskite film, resulting in a favorable doping profile that enhances carrier extraction. The fabricated device exhibits an outstanding open-circuit voltage (VOC) up to 1.34 V and achieves a certified efficiency of 19.31% for single-junction wide-bandgap (1.77 eV) perovskite solar cells, together with significantly enhanced operational stability, thanks to the improved separation of carriers. Furthermore, we demonstrate the potential of this wide-bandgap device by achieving a certified efficiency of 27.04% and a VOC of 2.12 V in a perovskite/perovskite tandem solar cell configuration.

Halide Perovskites-Based Diffusive Memristors for Artificial Mechano-Nociceptive System

Numerous efforts for emulating organ systems comprised of multiple functional units have driven substantial advancements in bio-realistic electronics and systems. The resistance change behavior observed in diffusive memristors shares similarities with the potential change in biological neurons. Here, the diffusive threshold switching phenomenon in Ag-incorporated organometallic halide perovskites is utilized to demonstrate the functions of afferent neurons. Halide perovskites-based diffusive memristors show a low threshold voltage of ≈0.2 V with little variation, attributed to the facile migration of Ag ions uniformly dispersed within the halide matrix. Based on the reversible and reliable volatile threshold switching, the memristors successfully demonstrate fundamental nociceptive functions including threshold firing, relaxation, and sensitization. Furthermore, to replicate the biological mechano-nociceptive phenomenon at a system level, an artificial mechano-nociceptive system is built by integrating a diffusive memristor with a force-sensing resistor. The presented system is capable of detecting and discerning the detrimental impact caused by a heavy steel ball, effectively exhibiting the corresponding sensitization response. By further extending the single nociceptive system into a 5 × 5 array, successful stereoscopic nociception of uneven impulses is achieved in the artificial skin system through array-scale sensitization. These results represent significant progress in the field of bio-inspired electronics and systems.

Electronic State Engineering in Perovskite-Cerium-Composite Nanocrystals toward Enhanced Triplet Annihilation Upconversion

Wavelength conversion based on hybrid inorganic-organic sensitized triplet-triplet annihilation upconversion (TTA-UC) is promising for applications such as photovoltaics, light-emitting-diodes, photocatalysis, additive manufacturing, and bioimaging. The efficiency of TTA-UC depends on the population of triplet excitons involved in triplet energy transfer (TET), the driving force in TET, and the coupling strength between the donor and acceptor. Consequently, achieving highly efficient TTA-UC necessitates the precise control of the electronic states of inorganic donors. However, conventional covalently bonded nanocrystals (NCs) face significant challenges in this regard. Herein, a novel strategy to exert control over electronic states is proposed, thereby enhancing TET and TTA-UC by incorporating ionic-bonded CsPbBr3 and lanthanide Ce3+ ions into composite NCs. These composite-NCs exhibit high photoluminescence quantum yield, extended single-exciton lifetime, quantum confinement, and uplifted energy levels. This engineering strategy of electronic states engendered a comprehensive impact, augmenting the population of triplet excitons participating in the TET process, enhancing coupling strength and the driving force, ultimately leading to an unconventional, dopant concentration-dependent nonlinear enhancement of UC efficiency. This work not only advances fundamental understanding of hybrid TTA-UC but also opens a door for the creation of other ionic-bonded composite NCs with tunable functionalities, promising innovations for next-generation optoelectronic applications.

Plasmon-Driven Photochemical Reduction Reaction on Silver Nanostructures for Green Fabrication of Superhydrophobic Surface

Green fabrication of superhydrophobic surface by water-based processing is still challenging, because introduction of the substances with hydrophilic moieties compromises its superhydrophobicity. Herein, a plasmon-driven photochemical reduction reaction under ultraviolet light (UVA) irradiation is first discovered and is applied to deoxygenation of hydrophilic organic adsorbates on rough nano-Ag coating for the formation of stable superhydrophobic surface. A nano-Ag coating with strong localized surface plasmon resonance in the UVA region is prepared by a water-based silver mirror reaction and results in a unique chemical reduction reaction on its surface. Consequently, the low residual hydrophilic functionalities and the formed cross-linked structure of the adsorbate on Ag nanoparticles (NPs) enables the coating to exhibit stable superhydrophobicity against to both air and water. The superhydrophobic Ag NP-coated sandpaper can also be used as a surface-enhanced Raman scattering (SERS) substrate to concentrate aqueous analytes for trace detection.

Interfacial dipole engineering in all-inorganic perovskite solar cells

Severe nonradiative recombination and energy level mismatch in perovskite solar cells (PSCs) are key factors affecting efficiency. Here, we report an effective strategy for surface passivation and interfacial dipole engineering of perovskite films. By precisely introducing electron-withdrawing and electron-donating groups on 7-azaindole, we have effectively controlled the passivation ability of N atoms and the polarity of the interfacial dipole, thereby regulating the perovskite surface's work function and obtaining the optimal energy level matching. This strategy yields an impressive efficiency of 10.76% for the CsPbBr3 PSC and exceptional stability.

Synergic Electron and Defect Compensation Minimizes Voltage Loss in Lead-Free Perovskite Solar Cells

Sn perovskite solar cells have been regarded as one of the most promising alternatives to the Pb-based counterparts due to their low toxicity and excellent optoelectronic properties. However, the Sn perovskites are notorious to feature heavy p-doping characteristics and possess abundant vacancy defects, which result in under-optimized interfacial energy level alignment and severe nonradiative recombination. Here, we reported a synergic "electron and defect compensation" strategy to simultaneously modulate the electronic structures and defect profiles of Sn perovskites via incorporating a traced amount (0.1 mol %) of heterovalent metal halide salts. Consequently, the doping level of modified Sn perovskites was altered from heavy p-type to weak p-type (i.e. up-shifting the Fermi level by ∼0.12 eV) that determinately reducing the barrier of interfacial charge extraction and effectively suppressing the charge recombination loss throughout the bulk perovskite film and at relevant interfaces. Pioneeringly, the resultant device modified with electron and defect compensation realized a champion efficiency of 14.02 %, which is ∼46 % higher than that of control device (9.56 %). Notably, a record-high photovoltage of 1.013 V was attained, corresponding to the lowest voltage deficit of 0.38 eV reported to date, and narrowing the gap with Pb-based analogues (∼0.30 V).

Atomic-scale imaging of ytterbium ions in lead halide perovskites

Lanthanide-doped lead halide perovskites have demonstrated great potential for photoelectric applications. However, there is a long-standing controversy about the existence of lanthanide ions, e.g., whether the doping of Ln3+ is successful or not; the substituting sites of Ln3+ in lead halide perovskites are unclear. We directly identify the doped Yb3+ in CsPbCl3 perovskites by using the state-of-the-art transmission electron microscopy and three-dimensional atom probe tomography at atomic scale. Different from the previous assumptions and/or results, we evidence that Yb3+ simultaneously replace Pb2+ and occupy the lattice interstitial sites. Furthermore, we directly observe the cluster phenomenon of CsPbCl3 single crystal at near atomic scale. Density functional theory modeling further confirms and explains the mechanisms of our findings. Our findings thus provide an atomic-level understanding of the doping mechanism in perovskites and will stimulate a further thinking of the doping effect on the performance of perovskites.

Performance Improvement of Lead-Based Halide Perovskites through B-Site Ion-Doping Strategies

Owing to their excellent properties, lead halide perovskites have attracted extensive attention in the photoelectric field. Presently, the certified power conversion efficiency of perovskite solar cells has reached 25.7%, the specific detectivity of perovskite photodetectors has exceeded 1014 Jones, and the external quantum efficiency of perovskite-based light-emitting diode has exceeded 26%. However, their practical applications are limited by the inherent instability induced by the perovskite structure due to moisture, heat, and light. Therefore, one of the widely used strategies to address the issue is to replace partial ions of the perovskites with ions of smaller radii to shorten the bond length between halides and metal cations, improving the bond energy and enhancing the perovskite stability. Particularly, the B-site cation in the perovskite structure can affect the size of eight cubic octahedrons and their gap. However, the X-site can only affect four such voids. This review comprehensively summarizes the recent progress in B-site ion-doping strategies for lead halide perovskites and provides some perspectives for further performance improvements.

Synergistic Optimization of Buried Interface by Multifunctional Organic-Inorganic Complexes for Highly Efficient Planar Perovskite Solar Cells

For the further improvement of the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs), the buried interface between the perovskite and the electron transport layer is crucial. However, it is challenging to effectively optimize this interface as it is buried beneath the perovskite film. Herein, we have designed and synthesized a series of multifunctional organic-inorganic (OI) complexes as buried interfacial material to promote electron extraction, as well as the crystal growth of the perovskite. The OI complex with BF4- group not only eliminates oxygen vacancies on the SnO2 surface but also balances energy level alignment between SnO2 and perovskite, providing a favorable environment for charge carrier extraction. Moreover, OI complex with amine (- NH2) functional group can regulate the crystallization of the perovskite film via interaction with PbI2, resulting in highly crystallized perovskite film with large grains and low defect density. Consequently, with rational molecular design, the PSCs with optimal OI complex buried interface layer which contains both BF4- and -NH2 functional groups yield a champion device efficiency of 23.69%. More importantly, the resulting unencapsulated device performs excellent ambient stability, maintaining over 90% of its initial efficiency after 2000 h storage, and excellent light stability of 91.5% remaining PCE in the maximum power point tracking measurement (under continuous 100 mW cm-2 light illumination in N2 atmosphere) after 500 h.

Transforming the Electrochemical Behaviors of Cobalt Oxide from "Supercapacitator" to "Battery" by Atomic-Level Structure Engineering for Inspiring the Advance of Co-Based Batteries

Cobalt-based electrodes receive emerging attention for their high theoretical capacity and rich valence variation ability, but state-of-the-art cobalt-based electrodes present performance far below the theoretical value. Herein, the in-depth reaction mechanisms in the alkaline electrolyte are challenged and proven to be prone to the surface-redox pseudocapacitor behavior due to the low adsorption energy to OH. Using the atomic-level structure engineering strategy after substitution metal searching, the adsorption energy is effectively enhanced, and the peak of CoOOH can be observed from in situ characterization for the first time, leading to the successful transition of charge storage behavior from "supercapacitor" to "battery". When used in a Zn-Co battery as a proof of concept, it shows comprehensive electrochemical performance with a flat discharge voltage plateau of ≈1.7 V, an optimal energy density of 506 Wh kg^-1 , and a capacity retention ratio of 85.1% after 2000 cycles, shining among the reported batteries. As a practical demonstration, this battery also shows excellent self-discharge performance with the capacity retention of 90% after a 10 h delay. This work subtly tunes the intrinsic electrochemical properties of the cobalt-based material through atomic-level structure engineering, opening a new opportunity for the advance of energy storage systems.

Operando Characterizations of Light-Induced Junction Evolution in Perovskite Solar Cells

Light-induced performance changes in metal halide perovskite solar cells (PSCs) have been studied intensively over the last decade, but little is known about the variation in microscopic optoelectronic properties of the perovskite heterojunctions in a completed device during operation. Here, we combine Kelvin probe force microscopy and transient reflection spectroscopy techniques to spatially resolve the evolution of junction properties during the operation of metal-halide PSCs and study the light-soaking effect. Our analysis showed a rise of an electric field at the hole-transport layer side, convoluted with a more reduced interfacial recombination rate at the electron-transport layer side in the PSCs with an n-i-p structure. The junction evolution is attributed to the effects of ion migration and self-poling by built-in voltage. Device performances are correlated with the changes of electrostatic potential distribution and interfacial carrier dynamics. Our results demonstrate a new route for studying the complex operation mechanism in PSCs.

Eliminating Nanocrystal Surface Light Loss and Ion Migration to Achieve Bright Mixed-Halide Blue Perovskite LEDs

Blue light-emittin g diodes (LEDs) are important components for perovskite electroluminescence applications, which still suffer from insufficient luminescence efficiency and poor stability. In Cl/Br mixed perovskite NCs, surficial defects cause severe light failure and ion migration, the in-depth mechanism of which is also not clear. To gain insights into these issues, we employ the ligand post-addition approach for mixed Cl/Br NCs by using octylammonium hydrobromide (OctBr) ligands, which effectively decrease surficial light loss and block ion migration pathways. The passivated CsPbCl_1.5Br_1.5 NCs exhibit exceptional blue emission with 95% PLQY, and the electroluminescence spectra of LEDs are located at the initial positions at the initial states. The treated NC blue devices show a negligible color shift as the voltage increases, which proves that electric-field-driven ion migration is drastically suppressed. In addition, OctBr-treated CsPbCl_1.5Br_1.5 and CsPbClBr₂ NC LEDs show high external quantum efficiencies of 2.42 and 3.05% for emission peaks at 456 and 480 nm, respectively. Our work identified the nature of NC surface defects and provided a surficial modification approach to develop high-performance and color-stable blue mixed-halide perovskite LEDs.

Metal Halide Perovskite/Electrode Contacts in Charge-Transporting-Layer-Free Devices

Metal halide perovskites have drawn substantial interest in optoelectronic devices in the past decade. Perovskite/electrode contacts are crucial for constructing high-performance charge-transporting-layer-free perovskite devices, such as solar cells, field-effect transistors, artificial synapses, memories, etc. Many studies have evidenced that the perovskite layer can directly contact the electrodes, showing abundant physicochemical, electronic, and photoelectric properties in charge-transporting-layer-free perovskite devices. Meanwhile, for perovskite/metal contacts, some critical interfacial physical and chemical processes are reported, including band bending, interface dipoles, metal halogenation, and perovskite decomposition induced by metal electrodes. Thus, a systematic summary of the role of metal halide perovskite/electrode contacts on device performance is essential. This review summarizes and discusses charge carrier dynamics, electronic band engineering, electrode corrosion, electrochemical metallization and dissolution, perovskite decomposition, and interface engineering in perovskite/electrode contacts-based electronic devices for a comprehensive understanding of the contacts. The physicochemical, electronic, and morphological properties of various perovskite/electrode contacts, as well as relevant engineering techniques, are presented. Finally, the current challenges are analyzed, and appropriate recommendations are put forward. It can be expected that further research will lead to significant breakthroughs in their application and promote reforms and innovations in future solid-state physics and materials science.

Two-dimensional BiTeI as a novel perovskite additive for printable perovskite solar cells

Hybrid organic-inorganic perovskite solar cells (PSCs) are attractive printable, flexible, and cost-effective optoelectronic devices constituting an alternative technology to conventional Si-based ones. The incorporation of low-dimensional materials, such as two-dimensional (2D) materials, into the PSC structure is a promising route for interfacial and bulk perovskite engineering, paving the way for improved power conversion efficiency (PCE) and long-term stability. In this work, we investigate the incorporation of 2D bismuth telluride iodide (BiTeI) flakes as additives in the perovskite active layer, demonstrating their role in tuning the interfacial energy-level alignment for optimum device performance. By varying the concentration of BiTeI flakes in the perovskite precursor solution between 0.008 mg mL^-1 and 0.1 mg mL^-1, a downward shift in the energy levels of the perovskite results in an optimal alignment of the energy levels of the materials across the cell structure, as supported by device simulations. Thus, the cell fill factor (FF) increases with additive concentration, reaching values greater than 82%, although the suppression of open circuit voltage (V _oc) is reported beyond an additive concentration threshold of 0.03 mg mL^-1. The most performant devices delivered a PCE of 18.3%, with an average PCE showing a +8% increase compared to the reference devices. This work demonstrates the potential of 2D-material-based additives for the engineering of PSCs via energy level optimization at perovskite/charge transporting layer interfaces.

Anchoring Vertical Dipole to Enable Efficient Charge Extraction for High-Performance Perovskite Solar Cells

Perovskite solar cells (PSCs) via two-step sequential method have received great attention in recent years due to their high reproducibility and low processing costs. However, the relatively high trap-state density and poor charge carrier extraction efficiency pose challenges. Herein, highly efficient and stable PSCs via a two-step sequential method are fabricated using organic-inorganic (OI) complexes as multifunctional interlayers. In addition to reduce the under-coordinated Pb2+ ions related trap states by forming interactions with the functional groups, the complexes interlayer tends to form dipole moment which can enhance the built-in electric field, thus facilitating charge carrier extraction. Consequently, with rational molecular design, the resulting devices with a vertical dipole moment that parallels with the built-in electric field yield a champion efficiency of 23.55% with negligible hysteresis. More importantly, the hydrophobicity of the (OI) complexes contributes to an excellent ambient stability of the resulting device with 91% of initial efficiency maintained after 3000 h storage.

Solid-State Lithium-Ion Batteries as a Method for Doping Halide Perovskites with an In Situ Optical Readout of Dopant Concentration

Controlled doping of halide perovskites is a longstanding challenge for efficient optoelectronic applications. Here, a solid-state lithium-ion battery (LIB) inspired device is used as a method of extrinsically doping a halide perovskite in a controlled and measurable fashion. The Burstein-Moss band gap shift induced by the electronic doping is measured using in situ optical spectroscopy to monitor the fraction of injected charges that successfully n-type dope the perovskite. By comparing the optical and electrochemical readouts of the charge density, we demonstrate a 96% doping efficiency during the insertion process. Subsequent charge removal steps demonstrate only a partial "undoping" of the perovskite, providing insights into the capacity degradation pathways in perovskite LIB electrodes.

A Sensitive and Rapid Wastewater Test for SARS-COV-2 and Its Use for the Early Detection of a Cluster of Cases in a Remote Community

Throughout the coronavirus disease 2019 (COVID-19) pandemic, wastewater surveillance has been used to monitor trends in severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) prevalence in the community. A major challenge in establishing wastewater surveillance programs, especially in remote areas, is the need for a well-equipped laboratory for sample analysis. Currently, no options exist for rapid, sensitive, mobile, and easy-to-use wastewater tests for SARS-CoV-2. The performance of the GeneXpert system, which offers cartridge-based, rapid molecular clinical testing for SARS-CoV-2 in a portable platform, was evaluated using wastewater as the input. The GeneXpert demonstrated a SARS-CoV-2 limit of detection in wastewater below 32 copies/mL with a sample processing time of less than an hour. Using wastewater samples collected from multiple sites across Canada during February and March 2021, a high overall agreement (97.8%) was observed between the GeneXpert assay and laboratory-developed tests regarding the presence or absence of SARS-CoV-2. Additionally, with the use of centrifugal filters, the detection threshold of the GeneXpert system was improved to <10 copies/mL in wastewater. Finally, to support on-site wastewater surveillance, GeneXpert testing was implemented in Yellowknife, a remote community in Northern Canada, where its use successfully alerted public health authorities to undetected transmission of COVID-19. The identification of SARS-CoV-2 in wastewater triggered clinical testing of recent travelers and identification of new COVID-19 cases/clusters. Taken together, these results suggest that GeneXpert is a viable option for surveillance of SARS-CoV-2 in wastewater in locations that do not have access to established testing laboratories. IMPORTANCE Wastewater-based surveillance is a powerful tool that provides an unbiased measure of COVID-19 prevalence in a community. This work describes a sensitive wastewater rapid test for SARS-CoV-2 based on a widely distributed technology, the GeneXpert. The advantages of an easy-to-use wastewater test for SARS-CoV-2 are clear: it supports surveillance in remote communities, improves access to testing, and provides faster results allowing for an immediate public health response. The application of wastewater rapid testing in a remote community facilitated the detection of a COVID-19 cluster and triggered public health action, clearly demonstrating the utility of this technology. Wastewater surveillance will become increasingly important in the postvaccination pandemic landscape as individuals with asymptomatic/mild infections continue transmitting SARS-CoV-2 but are unlikely to be tested.

Recent Advances in Hole-Transporting Layers for Organic Solar Cells

Global energy demand is increasing; thus, emerging renewable energy sources, such as organic solar cells (OSCs), are fundamental to mitigate the negative effects of fuel consumption. Within OSC's advancements, the development of efficient and stable interface materials is essential to achieve high performance, long-term stability, low costs, and broader applicability. Inorganic and nanocarbon-based materials show a suitable work function, tunable optical/electronic properties, stability to the presence of moisture, and facile solution processing, while organic conducting polymers and small molecules have some advantages such as fast and low-cost production, solution process, low energy payback time, light weight, and less adverse environmental impact, making them attractive as hole transporting layers (HTLs) for OSCs. This review looked at the recent progress in metal oxides, metal sulfides, nanocarbon materials, conducting polymers, and small organic molecules as HTLs in OSCs over the past five years. The endeavors in research and technology have optimized the preparation and deposition methods of HTLs. Strategies of doping, composite/hybrid formation, and modifications have also tuned the optical/electrical properties of these materials as HTLs to obtain efficient and stable OSCs. We highlighted the impact of structure, composition, and processing conditions of inorganic and organic materials as HTLs in conventional and inverted OSCs.

Reduction of Nonradiative Loss in Inverted Perovskite Solar Cells by Donor-π-Acceptor Dipoles

Inverted perovskite solar cells (IPSCs) attract growing interest because of their simple configuration, reliable stability, and compatibility with tandem applications. However, the power conversion efficiency (PCE) of IPSCs still lags behind their regular counterparts, mainly due to the more serious nonradiative loss. Here, we design three donor-π-acceptor (D-π-A) dipoles with various dipole moments to introduce extra electric fields at the interface of perovskites and electron transport materials via the binding between the carboxylate end group and under-coordinated divalent Pb. The chemical binding reduces the recombination centers, while the superposition of the built-in electric field facilitates the electron collection and the hole blocking. As a result, the nonradiative loss is diminished as the dipole moments of D-π-A dipoles increase, which contributes to a PCE of 21.4% with enhancement in both the open-circuit voltage and fill factor. The stability for an unencapsulated device is also improved due to the hydrophobic property of D-π-A dipoles.

Reducing Defects Density and Enhancing Hole Extraction for Efficient Perovskite Solar Cells Enabled by π-Pb2+ Interactions

Molecular doping is an of significance approach to reduce defects density of perovskite and to improve interfacial charge extraction in perovskite solar cells. Here, we show a new strategy for chemical doping of perovskite via an organic small molecule, which features a fused tricyclic core, showing strong intermolecular π-Pb²⁺ interactions with under-coordinated Pb²⁺ in perovskite. This π-Pb²⁺ interactions could reduce defects density of the perovskite and suppress the nonradiative recombination, which was also confirmed by the density functional theory calculations. In addition, this doping via π-Pb²⁺ interactions could deepen the surface potential and downshift the work function of the doped perovskite film, facilitating the hole extraction to hole transport layer. As a result, the doped device showed high efficiency of 21.41 % with ignorable hysteresis. This strategy of fused tricyclic core-based doping provides a new perspective for the design of new organic materials to improve the device performance.