Long-range charge carrier mobility in metal halide perovskite thin-films and single crystals via transient photo-conductivity

Ultrabright Blue Lead-Halide Perovskite Light-Emitting Diodes Based on Phosphonic Acid Functionalized Hole Injection Layer

Lead-halide perovskite light-emitting diodes (PeLEDs) are intrinsically capable of delivering high efficiency at high current densities compared to conventional solution-processed light-emitting diodes. While such performance and relevant high radiance have been well demonstrated in green and near-infrared ones, blue PeLEDs have lagged far behind due to extremely severe luminance-efficiency roll-off, especially in the pure-blue region (<480 nm, a CIEy coordinate below 0.15). Here, by tackling the critical limitations of phosphonic acid functional carbazoles (PACs) as hole injection layers and simultaneously leveraging their advantages on hole injection, we achieved ultrabright pure blue PeLEDs with minimized efficiency roll-off at high brightness with a CIEy coordinate below 0.15. We show that devices based on prevailing small-molecule PACs generally exhibit significant leakage currents. This is due to a synergistic effect of uneven surface coverage from reverse micelle formation and the nanoisland structure of thin-film lead-halide perovskite emitters. By using polymeric PACs instead, we demonstrate bright blue PeLEDs showing a peak luminance of ∼29 800 cd m-2 (478 nm, at a CIEy coordinate below 0.15). We also achieve a high brightness reaching ∼140 000 cd m-2 under pulsed driven. Our study not only provides a useful guidance for developing bright blue PeLEDs but also resolves a long-standing puzzle regarding the interfacial properties of PACs and their impact on hole transport, and it helps with the further design of these materials for lead-halide perovskite applications.

Chemical Reactivity-Controlled Synthesis of Silver Chalcogenide Colloidal Quantum Dots for Efficient Shortwave Infrared Photodetectors

Eco-friendly Ag2Te colloidal quantum dots (CQDs) have emerged as promising candidates for shortwave infrared (SWIR) optoelectronic applications owing to their size-tunable bandgaps with high optical properties. However, conventional synthesis methods relying on high temperatures and long reaction times yield low-quality Ag2Te CQDs because of their low chemical stability, resulting in decomposition under synthetic conditions and, thus, a non-uniform size distribution. Here, chemical reactivity-controlled synthesis is presented to regulate the crystal size and bandgap of Ag2Te CQDs. This involves adjusting the concentration and type of ligands, as well as the precursor ratio. The rapid termination of the reaction in this method prevents Ag2Te CQD decomposition, yielding monodisperse CQDs with a 1.66 peak-to-valley ratio at the first exciton absorption peak (≈1440 nm) and enabling absorption and emission in the 1100-1600 nm range. Furthermore, polar antisolvents in the purification process cause surface ligand removal from Ag2Te CQDs, resulting in surface defects and CQD aggregation. To mitigate these issues by enhancing their chemical stability, core/shell-type Ag2Te/Ag2S CQDs are synthesized. The photoluminescence (PL) intensity of Ag2Te/Ag2S CQDs significantly increased fivefold compared to Ag2Te core CQDs, and after purification, their size distribution remained uniform with preserved PL intensity. This is attributed to a significant reduction in surface defects. Consequently, the Ag2Te/Ag2S CQD-based SWIR photodetector exhibits a high external quantum efficiency of 8.4% and a specific detectivity of 1.1 × 1011 Jones at 1550 nm, with a fast response time of 38 ns.

Enhancing Charge Collection of Tin-Based Perovskite Solar Cells by Optimizing the Buried Interface with a Multifunctional Self-Assembled Monolayer

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a widely used hole transport material in inverted tin-based perovskite solar cells (Sn-PSCs). However, the efficiency and stability of these Sn-PSCs that utilize PEDOT:PSS are unsatisfactory, partly due to concerns about their mismatched work functions, hydrophobicity, and chemical interactions. Here, we introduce a self-assembled monolayer (SAM), (2-(7H-dibenzo[c,g]carbazol-7-yl)ethyl) phosphonic acid (2PADCB) as a multifunctional buffer molecule at the buried PEDOT:PSS/Sn perovskite interface. The phosphate group in the 2PADCB molecule reacts with the sulfur atom on the thiophene ring in PEDOT:PSS. This reaction process effectively anchors the SAM molecule firmly to the surface of PEDOT:PSS. Additionally, it reduces the binding sites between PEDOT and PSS, alleviating the acidification of the PEDOT:PSS surface and the poor conductivity caused by excessive PSS. Furthermore, the presence of two additional benzene rings in the 2PADCB molecule terminal group increases the electron density around Sn2+, thereby inhibiting its oxidation. Additionally, the hydrophobic characteristics of the 2PADCB molecule mitigate moisture infiltration from PEDOT:PSS, thereby protecting the degradation of Sn perovskite. Consequently, the Sn-PSCs based on the PEDOT:PSS/2PADCB film achieve a champion efficiency of 14.7%, higher than that of their pristine counterpart (12.5%). Moreover, the 2PADCB molecule improves the stability of the device by maintaining 90% of its initial efficiency after 160 h under 1 Sun illumination. Such enhancement in efficiency and stability is mainly attributed to the improved interface quality with the 2PADCB molecule, leading to better carrier transport and suppressed charge recombination at the buried PEDOT:PSS/Sn perovskite interface. Our work suggests that introducing the 2PADCB molecule at the PEDOT:PSS/perovskite interface is a promising method for efficient and stable Sn-PSCs.

Steering perovskite precursor solutions for multijunction photovoltaics

Multijunction photovoltaics (PVs) are gaining prominence owing to their superior capability of achieving power conversion efficiencies (PCEs) beyond the radiative limit of single-junction cells1-8, for which improving narrow-bandgap (NBG) tin-lead perovskites is critical for thin-film devices9. Here, with a focus on understanding the chemistry of tin-lead perovskite precursor solutions, we find that Sn(II) species dominate interactions with precursors and additives and uncover the exclusive role of carboxylic acid in regulating solution colloidal properties and film crystallization and ammonium in improving film optoelectronic properties. Materials that combine these two functional groups, amino acid salts, considerably improve the semiconducting quality and homogeneity of perovskite films, surpassing the effect of the individual functional groups when introduced as part of separate molecules. Our enhanced tin-lead perovskite layer allows us to fabricate solar cells with PCEs of 23.9%, 29.7% (certified 29.26%) and 28.7% for single-junction, double-junction and triple-junction devices, respectively. Our 1-cm2 triple-junction devices show PCEs of 28.4% (certified 27.28%). Encapsulated triple-junction cells maintain 80% of their initial efficiencies after 860 h maximum power point tracking (MPPT) in ambient. We further fabricate quadruple-junction devices and obtain PCEs of 27.9% with the highest open-circuit voltage of 4.94 V. This work establishes a new benchmark for multijunction PVs.

Back-Contact Perovskite Solar Cell Modules Fabricated via Roll-to-Roll Slot-Die Coating: Scale-Up toward Manufacturing

We fabricate a type of back-contact perovskite solar cell based on 1.5 μm-width grooves that are embossed into a plastic film whose opposing "walls" are selectively coated with either n- or p-type contacts. A perovskite precursor solution is then deposited into the grooves, creating individual photovoltaic devices. Each groove device is series-connected to its neighbors, creating minimodules consisting of hundreds of connected grooves. Here, we report on the fabrication of groove-based devices using slot-die coating to deposit the perovskite precursor and explore the structure of the perovskite in the grooves using a range of microscopy and spectroscopy techniques. Significantly, our devices do not contain any expensive or scarce elements such as indium, indicating that this technology is both sustainable and low-cost. Furthermore, all coating processes explored here were performed using roll-to-roll processing techniques. Our technology is therefore completely scalable and is consistent with high-throughput, low-cost manufacturing.

Carrier recombination dynamics in [MAPbCl3]x[CsPbBr3]1-x shell-passivated CsPbBr3 single crystals

As one of the commonly used methods for surface passivation of semiconductors, a heterostructure method was developed in this work to passivate surface traps of CsPbBr3 single crystals (SCs), and further, this method was correlated with carrier recombination processes. Herein, carrier recombination processes in bare and [MAPbCl3]0.34[CsPbBr3]0.66-covered CsPbBr3 SCs were studied using time-resolved spectroscopic techniques, including steady-state and time-resolved photoluminescence (TRPL) spectroscopy and time-resolved microwave photoconductivity (TRMC). By comparing the kinetics of TRPL and TRMC, we concluded that surface hole-trapping process dominates the TRPL kinetics of bare CsPbBr3 SCs and surface electron-trapping process dominates the slower decay component in TRMC. By studying carrier recombination processes of CsPbBr3 SCs with and without choline bromide (CB) additives, we found that the use of CB could introduce additional surface electron and hole traps. For CsPbBr3 SCs with a shell, we observed charge carrier transfer from the shell to the CsPbBr3 crystal. We found that the [MAPbCl3]0.34[CsPbBr3]0.66 shell can reduce the electron-trapping and hole-trapping rates by 2.2 times and 5.2 times, respectively, indicating that the [MAPbCl3]0.34[CsPbBr3]0.66 shell can passivate the surface traps of CsPbBr3 crystals effectively.

Steady state and transient absorption spectroscopy in metal halide perovskites

Metal halide perovskites (MHPs) have emerged as the most promising materials due to superior optoelectronic properties and great applications spanning from photovoltaics to photonics. Absorption spectroscopy provides a broad and deep insight into the carrier dynamics of MHPs, and is a critical complement to fluorescence and scattering spectroscopy. However, absorption spectroscopy is often misunderstood or underestimated, being seen as UV-vis spectroscopy only, which can lead to various misinterpretations. In fact, absorption spectroscopy is one of the most important branches of spectroscopic techniques (others including fluorescence and scattering), which plays a critical role in understanding the electronic structure and optoelectrical dynamics of MHPs. In this tutorial, the basic principles of various types of absorption spectroscopy as well as their recent developments and applications in MHP materials and devices are summarized, covering comprehensive advances in steady state and transient absorption spectroscopy. Given the significance of absorption spectroscopy in directing the design of different optoelectronic applications of MHPs, this tutorial will comprehensively discuss absorption spectroscopy, covering wavelengths from optical to terahertz (THz) and microwave, and timescales from femtoseconds to hours, and it specifically focuses on time-dependent steady-state and transient absorption spectroscopy under light illumination bias to study MHP materials and devices, allowing researchers to select suitable characterization techniques.

Analyzing Efficiency of Perovskite Solar Cells Under High Illumination Intensities by SCAPS Device Simulation

The perovskite solar cell (PSC) is undergoing intense study to meet sustainable energy and environmental demands. However, large-sized solar cells will degrade the power conversion efficiency, thus concentrating light on small-size devices would be a solution. Here, we report the performance of a p-i-n structured device using CH3NH3PbI3 (MAPbI3) as the active layer with an area of 6 mm2. We prove that the power output would be up to 4.2 mW under 10 Suns compared to the 0.9 mW obtained under 1 Sun; however, this results in an actual efficiency drop of the PSC. Further, using a SCAPS device simulation, we found that the intrinsic properties, such as mobility and defect density, of MAPbI3 has no profound influence on the relationship between light intensity and power conversion efficiency (PCE), but the series resistance is the dominant limiting factor on the performance of the PSC under high illumination intensities. Our work suggests the potential of perovskite in concentrating photovoltaics and makes recommendations for future development.

Tuning electronic structure and carrier transport properties through crystal orientation control in two-dimensional Dion-Jacobson phase perovskites

Two-dimensional halide perovskites are attracting attention due to their structural diversity, improved stability, and enhanced quantum efficiency compared to their three-dimensional counterparts. In particular, Dion-Jacobson (DJ) phase perovskites exhibit superior structural stability compared to Ruddlesden-Popper phase perovskites. The inherent quantum well structure of layered perovskites leads to highly anisotropic charge transport and optical properties. Therefore, controlling the preferred crystal orientation (parallel or perpendicular) is crucial for optimizing device performance. This work presents a rational strategy to control parallel and perpendicular crystal growth in C6N2H16PbI4 (4AMPPbI4)-based DJ phase perovskite thin films. We demonstrate that crystal orientation depends on crystal growth rates, which can be controlled by varying the solvent composition, antisolvent, and annealing temperature. Direct and inverse photoelectron spectroscopy reveals that the electronic structure of 4AMPPbI4, including its work function, ionization energy, and electron affinity, is orientation-dependent. Different orientations significantly affect carrier transport as confirmed by single-carrier devices. This study highlights the critical role of crystal orientation in DJ phase perovskites for designing high-performance optoelectronic devices.

Bidirectional Photovoltage-Driven Oxide Transistors for Neuromorphic Visual Sensors

Biological vision is one of the most important parts of the human perception system. However, emulating biological visuals is challenging because it requires complementary photoexcitation and photoinhibition. Here, the study presents a bidirectional photovoltage-driven neuromorphic visual sensor (BPNVS) that is constructed by monolithically integrating two perovskite solar cells (PSCs) with dual-gate ion-gel-gated oxide transistors. PSCs act as photoreceptors, converting external visual stimuli into electrical signals, whereas oxide transistors generate neuromorphic signal outputs that can be adjusted to produce positive and negative photoresponses. This device mimics the human vision system's ability to recognize colored and color-mixed patterns. The device achieves a static color recognition accuracy of 96% by utilizing the reservoir computing system for feature extraction. The BPNVS mem-reservoir chip is also proposed for handing object movement and dynamic color recognition. This work is a significant step forward in neuromorphic sensing and complex pattern recognition.

Ultrafast Carrier Diffusion in Perovskite Monocrystalline Films

Monocrystalline perovskite materials exhibit superior properties compared with polycrystalline perovskites, including lower defect density, minimal grain boundaries, and enhanced carrier mobility. Nevertheless, the preparation of large-area, high-quality single-crystal films, which could prove invaluable for photoelectronic applications, remains a significant challenge. The study of how their unique properties go beyond polycrystalline thin films is still missing. In our experiment, using polarization-selective transient absorption microscopy, we directly observed the spatial carrier transportation in methylammonium lead iodide (CH3NH3PbI3, MAPbI3) strip-shaped monocrystalline ultrathin films. Ultrafast carrier diffusion transportation was observed. The monocrystalline carrier diffusion coefficient D (∼22 cm2 s-1) is an order of magnitude higher than that in polycrystalline films. Anisotropic carrier diffusion of the MAPbI3 single crystal has been discovered. It is also discovered that the electrons and holes are of different anisotropy and diffusion speed. This ultralong carrier transport inside the monocrystalline film provides solid support for the development of perovskite based photoelectronic devices.

Optimization of CsPbBr3/PVDF composite for enhanced UV photodetection application

Halide perovskites have exhibited great research impact for developing innovative materials with novel properties. Here, we report the synthesis of different caesium lead bromide perovskites using different (Cs/Pb) molar ratios and fabrication of their corresponding perovskite/polyvinylidene fluoride (PVDF) composites, as well as study of their structural and UV-photodetection properties. Spin-coated perovskite/PVDF composite thin films revealed strong oriented XRD diffraction peaks along the c-axis direction (00l) with homogeneously distributed perovskite microcrystals in the polymer matrix. The high-Cs containing perovskite/PVDF composite, with Cs/Pb (3/1) molar ratio, demonstrated the highest green emission under UV light and its corresponding UV-photodetector exhibited the highest UV photo-responsivity. These results highlight the importance of structural modulation and additive manufacturing for tailoring the optoelectronic properties of halide perovskites.

Enhanced Carrier Lifetime and Mobility in Monolayer NbOI2

The lifetime and mobility of hot carriers are critical parameters for assessing the performance of optoelectronic materials, as they directly impact the response speed and operational efficiency of devices. Combining first-principles calculations with nonadiabatic molecular dynamics (NAMD) simulations, we systematically investigated the electronic properties and carrier dynamics of monolayer NbOI2. Our findings indicate that, at room temperature, this material demonstrates a carrier lifetime of up to ∼13 ns and an electron mobility reaching as high as ∼9 × 103 cm2 V-1 s-1. The low Young's modulus makes it susceptible to deformation under external stress, and we found that the carrier lifetime extends to ∼40 ns under a 4% tensile strain, along with a significant increase in hole mobility. This study elucidates the carrier dynamics in monolayer NbOI2, facilitating its potential application in future flexible optoelectronic devices.

Bandgap Engineering via Doping Strategies for Narrowing the Bandgap below 1.2 eV in Sn/Pb Binary Perovskites: Unveiling the Role of Bi3+ Incorporation on Different A-Site Compositions

The integration of perovskite materials in solar cells has garnered significant attention due to their exceptional photovoltaic properties. However, achieving a bandgap energy below 1.2 eV remains challenging, particularly for applications requiring infrared absorption, such as sub-cells in tandem solar cells and single-junction perovskite solar cells. In this study, we employed a doping strategy to engineer the bandgap and observed that the doping effects varied depending on the A-site cation. Specifically, we investigated the impact of bismuth (Bi3+) incorporation into perovskites with different A-site cations, such as cesium (Cs) and methylammonium (MA). Remarkably, Bi3+ doping in MA-based tin-lead perovskites enabled the fabrication of ultra-narrow bandgap films (~1 eV). Comprehensive characterization, including structural, optical, and electronic analyses, was conducted to elucidate the effects of Bi doping. Notably, 8% Bi-doped Sn-Pb perovskites demonstrated infrared absorption extending up to 1360 nm, an unprecedented range for ABX3-type single halide perovskites. This work provides valuable insights into further narrowing the bandgap of halide perovskite materials, which is essential for their effective use in multi-junction tandem solar cell architectures.

Ambient Air Processed Inverted Inorganic Perovskite Solar Cells with over 21 % Efficiency Enabled by Multifunctional Ethacridine Lactate

All-inorganic cesium lead triiodide perovskites (CsPbI3) have attracted increasing attention due to their good thermal stability, remarkable optoelectronic properties, and adaptability in tandem solar cells. However, N2-filled glovebox is generally required to strictly control the humidity during film fabrication due to the moisture-induced black-to-yellow phase transition, which remains a great hinderance for further commercialization. Herein, we report an effective approach via incorporating multifunctional ethacridine lactate (EAL) to mitigate moisture invasion and enable the fabrication of efficient inverted (p-i-n) CsPbI3 perovskite solar cells (PSCs) under ambient condition. It is revealed that the lactate anions accelerate the crystallization of CsPbI3, shortening the exposure time to moisture during film fabrication. Meanwhile, the conjugated backbone and multiple functional groups in the ethacridine cations can interact with I- and Pb2+ to reduce the undesired defects, stabilize the perovskite structure and facilitate the charge transport in the film. Moreover, EAL incorporation also leads to better energy alignment, thus favoring charge extraction at both upper and bottom interfaces. Consequently, the device efficiency and stability are enormously enhanced, with the champion efficiency reaching 21.08 %. This even surpasses the highest value reported for the devices fabricated in glovebox, representing a record efficiency of inverted all-inorganic PSCs.

Managing Interfacial Defects and Charge-Carriers Dynamics by a Cesium-Doped SnO2 for Air Stable Perovskite Solar Cells

A high-quality nanostructured tin oxide (SnO2) has garnered massive attention as an electron transport layer (ETL) for efficient perovskite solar cells (PSCs). SnO2 is considered the most effective alternative to titanium oxide (TiO2) as ETL because of its low-temperature processing and promising optical and electrical characteristics. However, some essential modifications are still required to further improve the intrinsic characteristics of SnO2, such as mismatch band alignments, charge extraction, transportation, conductivity, and interfacial recombination losses. Herein, an inorganic-based cesium (Cs) dopant is used to modify the SnO2 ETL and to investigate the impact of Cs-dopant in curing interfacial defects, charge-carrier dynamics, and improving the optoelectronic characteristics of PSCs. The incorporation of Cs contents efficiently improves the perovskite film quality by enhancing the transparency, crystallinity, grain size, and light absorption and reduces the defect states and trap densities, resulting in an improved power conversion efficiency (PCE) of ≈22.1% with Cs:SnO2 ETL, in-contrast to pristine SnO2-based PSCs (20.23%). Moreover, the Cs-modified SnO2-based PSCs exhibit remarkable environmental stability in a relatively higher relative humidity environment (>65%) and without encapsulation. Therefore, this work suggests that Cs-doped SnO2 is a highly favorable electron extraction material for preparing highly efficient and air-stable planar PSCs.

Solid-State Anion Exchange Enabled by Pluggable vdW Assembly for In Situ Halide Manipulation in Perovskite Monocrystalline Film

The fabrication of perovskite single crystal-based optoelectronics with improved performance is largely hindered by limited processing techniques. Particularly, the local halide composition manipulation, which dominates the bandgap and thus the formation of heterostructures and emission of multiple-wavelength light, is realized via prevalent liquid- or gas-phase anion exchange with the utilization of lithography, while the monocrystalline nature is sacrificed due to polycrystalline transition in exchange with massive defects emerging, impeding carrier separation and transportation. Thus, a damage-free and lithography-free solid-state anion exchange strategy, aiming at in situ halide manipulation in perovskite monocrystalline film, is developed. Typically, CsPbCl3 working as medium to deliver halide is van der Waals (vdW) assembled to specific spots of CsPbBr3, followed by the removal of CsPbCl3 after anion exchange, with the halide composition in contact area modulated and monocrystalline nature of CsPbBr3 preserved. CsPbBr3-CsPbBrxCl3-x monocrystalline heterostructure has been achieved without lithography. Device based on the heterostructure shows apparent rectification behavior and improved photo-response rate. Heterostructure arrays can also be constructed with customized medium crystal. Furthermore, the halide composition can be accurately tuned to enable full coverage of visible spectra. The solid-state exchange enriches the toolbox for processing vulnerable perovskite and paves the way for the integration of monocrystalline perovskite optoelectronics.

Identification and Suppression of Point Defects in Bromide Perovskite Single Crystals Enabling Gamma-Ray Spectroscopy

Methylammonium lead tribromide (MAPbBr3) stands out as the most easily grown wide-band-gap metal halide perovskite. It is a promising semiconductor for room-temperature gamma-ray (γ-ray) spectroscopic detectors, but no operational devices are realized. This can be largely attributed to a lack of understanding of point defects and their influence on detector performance. Here, through a combination of crystal growth design and defect characterization, including positron annihilation and impedance spectroscopy, the presence of specific point defects are identified and correlated to detector performance. Methylammonium (MA) vacancies, MA interstitials, and Pb vacancies are identified as the dominant charge-trapping defects in MAPbBr3 crystals, while Br vacancies caused doping. The addition of excess MABr reduces the MA and Br defects and so enables the detection of energy-resolved γ-ray spectra using a MAPbBr3 single-crystal device. Interestingly, the addition of formamidinium (FA) cations, which converted to methylformamidinium (MFA) cations by reaction with MA+ during crystal growth further reduced MA defects. This enabled an energy resolution of 3.9% for the 662 keV 137Cs line using a low bias of 100 V. The work provides direction toward enabling further improvements in wide-bandgap perovskite-based device performance by reducing detrimental defects.

Size Dependence of Ultrafast Electron Transfer from Didodecyl Dimethylammonium Bromide-Modified CsPbBr3 Nanocrystals to Electron Acceptors

Charge transfer efficiencies in all-inorganic lead halide perovskite nanocrystals (NCs) are crucial for applications in photovoltaics and photocatalysis. Herein, CsPbBr3 NCs with different sizes are synthesized by varying the ligand contents of didodecyl dimethylammonium bromide at room temperature. Adding benzoquinone (BQ) molecules leads to a decrease in the PL intensities and PL decay times in NCs. The electron transfer (ET) efficiency (ηET) increases with NC size in complexes of CsPbBr3 NCs and BQ molecules (NC-BQ complexes), when the same concentration of BQ is maintained, as investigated by transient photobleaching and photoluminescence spectroscopies. Controlling the same number of attached BQ acceptor molecules per NC induces the same ηET in NC-BQ complexes even though with different NC sizes. Our findings provide new insights into ultrafast charge transfer behaviors in perovskite NCs, which is important for designing efficient light energy conversion devices.

Unraveling Defect-Mediated Enhancement of Transient Photoconductivity and Slower Carrier's Mobility Decay in Cu-Doped Cs2AgBiBr6 Nanocrystals Using Ultrafast Pump-Probe Spectroscopy

Lead-free double perovskite nanocrystals (A2B'(III)B″(I)X6 NCs) address the instability and toxicity concerns of lead-based counterparts, but their device performance is limited by subpar absorption and unexplored carrier dynamics. Impurity ion doping offers a route to tune electrical conductivity and charge carrier transport. Herein, we synthesized Cu-doped Cs2AgBiBr6 (CABB) nanocrystals using a hot-injection approach and investigated the charge carrier's dynamics through ultrafast pump-probe spectroscopy. Copper introduction into the CABB lattice enhanced absorption in the near-infrared region and introduced sub-band gap defect states in CABB NCs. The transient absorption study revealed a faster bleach decay with increased copper doping, as a result of charge transfer from the conduction band to copper defect states. Also, an optical pump terahertz probe study displays higher photoconductivity and mobility in Cu-doped CABB NCs. Slower mobility decay in Cu-doped systems was attributed to the charge carrier's entrapment at the defect state. These findings suggest that copper-doped CABB is a superior contender for optoelectronic applications over conventional CABB.

Synthesis of different organic ammonium-based bismuth iodide perovskites for photodetection application

Bismuth-based perovskites are promising candidates for highly stable halide perovskites with low toxicity. Here, we report the synthesis of a series of bismuth iodide-based perovskites with different primary, secondary, and tertiary ammonium cations and study their structural, thermal, and optical properties, and the likelihood of photodetection. Interestingly, the variation of A-site organic ammonium cations, with different interlayer spacings between adjacent bismuth iodide monolayers, has exotic effects on the diffraction patterns and morphological structures of the perovskite crystals. Thermogravimetric analysis reveals the highest thermal stability of tertiary ammonium-based bismuth perovskite with a decomposition temperature of 385 °C. The branched primary ammonium-based photodetector has photo-responsivity roughly two and four times faster than that of secondary and tertiary ammonium-based devices, respectively. These findings provide insight into the importance of A-site cation engineering for structural modulation and tailoring the optoelectronic properties of bismuth-based perovskites for emerging optoelectronic devices.

Elucidating Charge Carrier Dynamics in Perovskite-Based Tandem Solar Cells

Recently, multijunction tandem solar cells (TSCs) have presented high power conversion efficiency and revealed their immense potential in photovoltaic evolution. It is demonstrated that multiple light absorbers with various bandgap energies overcome the Shockley-Queisser limit of single-junction solar cells by absorbing the wide-range wavelength photons. Here, the main key challenges are reviewed, especially the charge carrier dynamics in perovskite-based 2-terminal (2-T) TSCs in terms of current matching, and how to manage these issues from a vantage point of characterization. To do this, the effect of recombination layers, optical and fabrication hurdles, and the impact of wide bandgap perovskite solar cells are discussed extensively. Afterward, this review focuses on various optoelectronics, spectroscopic, and theoretical (optical simulation) characterizations to figure out those issues, especially current-matching issues faced by the photovoltaic society. This review comprehensively provides deep insights into the relationship between the current-matching problems and the photovoltaic performance of TSCs through a variety of perspectives. Consequently, it is believed that this review is essential to address the main problems of 2-T TSCs, and the suggestions to elucidate the charge carrier dynamics and its characterization may pave the way to overcome such obstacles to further improve the development of 2-T TSCs in relation to the current-matching problems.

Tailoring passivators for highly efficient and stable perovskite solar cells

There is an ongoing global effort to advance emerging perovskite solar cells (PSCs), and many of these endeavours are focused on developing new compositions, processing methods and passivation strategies. In particular, the use of passivators to reduce the defects in perovskite materials has been demonstrated to be an effective approach for enhancing the photovoltaic performance and long-term stability of PSCs. Organic passivators have received increasing attention since the late 2010s as their structures and properties can readily be modified. First, this Review discusses the main types of defect in perovskite materials and reviews their properties. We examine the deleterious impact of defects on device efficiency and stability and highlight how defects facilitate extrinsic degradation pathways. Second, the proven use of different passivator designs to mitigate these negative effects is discussed, and possible defect passivation mechanisms are presented. Finally, we propose four specific directions for future research, which, in our opinion, will be crucial for unlocking the full potential of PSCs using the concept of defect passivation.

Exploring the Role of Short Chain Acids as Surface Ligands in Photoinduced Charge Transfer Dynamics from CsPbBr3 Perovskite Nanocrystals

The most commonly used surface capping ligands, like oleic acid and oleylamine, passivate the surface of perovskite nanocrystals (PNCs) to enhance their stability and optical properties. However, due to their inherent insulating nature, charge transport across the surface of the PNCs is hindered, limiting their application in devices. In this study, we have post-treatment CsPbBr₃ PNCs with short chain ligands benzoic acid (BA) and ascorbic acid (AA) and observed that both acid-treated PNCs show enhanced stability and optical properties. Still, BA-treated PNCs show the highest charge transport rate due to their conjugating nature. The photoelectrochemical measurements also show the most efficient electron flow across the surface of the PNC with BA-treated PNCs. A longer carrier lifetime and fast charge transfer make BA-treated PNCs ideal candidates for application in real-life devices.