In Situ Iodide Passivation Toward Efficient CsPbI3 Perovskite Quantum Dot Solar Cells

Application of advanced quantum dots in perovskite solar cells: synthesis, characterization, mechanism, and performance enhancement

Quantum dots have garnered significant interest in perovskite solar cells (PSCs) due to their stable chemical properties, high carrier mobility, and unique features such as multiple exciton generation and excellent optoelectronic characteristics resulting from quantum confinement effects. This review explores quantum dot properties and their applications in photoelectronic devices, including their synthesis and deposition processes. This sets the stage for discussing their diverse roles in the carrier transport, absorber, and interfacial layers of PSCs. We thoroughly examine advances in defect passivation, energy band alignment, perovskite crystallinity, device stability, and broader light absorption. In particular, novel approaches to enhance the photoelectric conversion efficiency (PCE) of quantum dot-enhanced perovskite solar cells are highlighted. Lastly, based on a comprehensive overview, we provide a forward-looking outlook on advanced quantum dot fabrication and its impact on enhancing the photovoltaic performance of solar cells. This review offers insights into fundamental mechanisms that endorse quantum dots for improved PSC performance, paving the way for further development of quantum dot-integrated PSCs.

Transparent and flexible cellulose based luminescent film for multifunctional applications

Metal halide perovskite quantum dots (QDs) film shows significant potential in flexible optoelectronics, including applications in lighting, displays, wearable devices and non-planar X-ray imaging. However, developing highly luminescent, durable, and mechanical flexible film for practical use remains a challenge. In this study, we introduce a low-cost, environmentally friendly, biomass material - mixed cellulose esters (MCE) - as a novel encapsulation matrix. The CsPbBr3@MCE composite luminescent film was fabricated using a simple in-situ growth strategy, ensuring uniform distribution of QDs within the matrix. The chemical bond anchoring between MCE and CsPbBr3 QDs, combined with the effective isolation provided by in-situ encapsulation, resulted in exceptional luminescence properties, including a high photoluminescence quantum yield (PLQY = 67.73 %) and excellent color purity. Additionally, the film demonstrated enhanced stability against environmental, thermal, ultraviolet, and high-humidity stresses, thanks to the protective encapsulation of MCE. It also exhibited remarkable mechanical flexibility, transparency, the capability for large-area production. These findings suggest that the CsPbBr3@MCE composite holds great promise for various applications, including light-emitting diodes, flexible pattern display, hazardous chemical identification, information encryption, and anti-counterfeiting technologies.

Caesium-Iodide-Assisted Synthesis of High-Quality, Stable, and Robust Lead-Free Perovskite Quantum Dots

The poor morphology, and susceptibility to oxidation of tin-based perovskite quantum dots (TQDs) have posed significant challenges, limiting their application potential. This study presents a straightforward method for synthesizing high-quality CsSnI3-based perovskite quantum dots (TQDs) by incorporating a mixed Cs source of Cs2CO3 and CsI. The addition of CsI increased the I:Sn ratio while maintaining Sn:Cs, resulting in TQDs with smaller size and improved uniformity. X-ray photoelectron spectroscopy (XPS), and Nuclear magnetic resonance (NMR) analyses confirmed enhanced crystallinity, photoluminescence intensity, and antioxidation ability of CsI-TQDs. Remarkably, these TQDs exhibit exceptional stability, enduring over 1 h in air and more than 24 h before complete oxidation, surpassing the previously reported longest lifetime in air for TQDs with conventional oleic acid (OA) and oleylamine (OAm) ligands. Furthermore, these TQD films retain robustness after ligand exchange with methyl acetate (MeOAc) and formamidinium iodide (FAI), representing the first successful short-ligand exchange of TQDs and enabling further electronic device applications. These findings suggest that CsI in the Cs source plays a crucial role in facilitating the formation of surface complexes, regulating TQD growth and suppressing iodine vacancies.

Surface chemistry-engineered perovskite quantum dot photovoltaics

The discovery and synthesis of colloidal quantum dots (QDs) was awarded the Nobel Prize in Chemistry in 2023. Recently, the development of bulk metal halide perovskite semiconductors has generated intense interest in their corresponding perovskite QDs. QDs, more broadly known as nanocrystals, constitute a new class of materials that differ from both molecular and bulk materials. They have rapidly advanced to the forefront of optoelectronic applications owing to their unique size-, composition-, surface- and process-dependent optoelectronic properties. More importantly, their ultrahigh surface-area-to-volume ratio enables various surface chemistry engineering strategies to tune and optimize their optoelectronic properties. Finally, three-dimensional confined QDs, offering nearly perfect photoluminescent quantum yield, slow hot-carrier cooling time, especially their colloidal synthesis and processing using industrially friendly solvents, have revolutionized the fields of electronics, photonics, and optoelectronics. Particularly, in emerging perovskite QD-based PVs, the advancement of surface chemistry has boosted the record power conversion efficiency (PCE) to 19.1% within a five-year period, surpassing all other colloidal QD photovoltaics (PVs). Given the rapid enhancement of device performances, perovskite QD PVs have attracted significant attention. Further study of semiconducting perovskite QDs will lead to advanced surface structures, a deeper understanding of halide perovskites, and enhanced PCE. In this review article, we comprehensively summarize and discuss the emerging perovskite QD PVs, providing insights into the impact of surface chemical design on their electronic coupling, dispersibility, stability and defect passivation. The limitations of current perovskite QDs mainly arise from their "soft" ionic nature and dynamic surface equilibrium, which lead to difficulties in the large-scale synthesis of monodispersed perovskite QDs and conductive inks for high-throughput printing techniques. We present that the development of surface chemistry is becoming a platform for further improving PCE, aiming to reach the 20% milestone. Additionally, we discuss integrating artificial intelligence to facilitate the mass-production of perovskite QDs for large-area, low-cost PV technology, which could help address significant energy challenges.

A Brief Review of Perovskite Quantum Dot Solar Cells: Synthesis, Property and Defect Passivation

Perovskite quantum dot solar cells (PQDSCs), as the promising candidate for the next generation of solar cell, have garnered the significant attention over the past decades. However, the performance and stability of PQDSCs are highly dependent on the properties of interfaces between the perovskite quantum dots (PQDs) and the other layers in the device. This work provides a brief overview of PQDSCs, including the synthesis of PQDs, the characteristics and preparation methods of PQDs, the photoelectric properties as the light absorption layer and optimization methods for PQDSCs with high efficiency. Future directions and potential applications are also highlighted.

Systematic Study of the Synthesis of Monodisperse CsPbI3 Perovskite Nanoplatelets for Efficient Color-Pure Light Emitting Diodes

Metal halide perovskite nanoplatelets (NPls) possess ultra-narrow photoluminescence (PL) bands tunable over the entire visible spectral range, which makes them promising for utilization in light-emitting diodes (LEDs) with spectrally pure emission colors. This calls for development of synthetic methods toward perovskite NPls with a high degree of control over both their thickness and lateral dimensions. A general strategy is developed to obtain such monodisperse CsPbI3 NPls through the control over the halide-to-lead ratio during heating-up reaction. The excess of iodine precursor changes the chemical equilibrium, thus yielding monodisperse (3 monolayers in thickness) CsPbI3 NPls whose PL width constitutes ≈22 nm, while the lateral dimensions of NPls are determined by choice of precursor and by the reaction temperature. Postsynthetic cation exchange on the A-site of the perovskite lattice allows for the tuning of the PL peak position, while simultaneous removal of the excess ligands and the surface passivation allows for improvement of the PL quantum yield to 96% and ensures superior stability of optical properties upon storage. Electroluminescent LEDs with the peak values are fabricated for the external quantum efficiency and luminance being 9.45% and 29800 cd m-2, respectively, and a narrow (≈26 nm) electroluminescence peak at 601 nm.

PCBM Constructing Heterojunction for Efficient CsPbI3 Perovskite Quantum Dot Solar Cells

CsPbI3 perovskite quantum dots (PQDs) have emerged as promising photovoltaic materials for third-generation solar cells, owing to their superior optoelectronic properties. Nevertheless, the performance of CsPbI3 PQD solar cells is primarily hindered by low carrier extraction efficiency, largely due to the insulative ligands. In this study, we introduced a semiconductor molecule, [6,6]-phenyl C61 butyric acid methyl ester (PCBM), onto the surfaces of CsPbI3 PQDs as surface ligands to enhance photogenerated charge extraction. The results indicate that PCBM accelerates carrier separation in CsPbI3 PQDs by forming a type II heterojunction, and also modulates the energy level of CsPbI3 PQDs by altering surface dipole moments. Additionally, we established an energy-level gradient alignment in the PCBM/CsPbI3 PQD heterojunction absorber layer, which was found to effectively promote carrier extraction and reduce carrier recombination loss in PQD solar cells. Ultimately, the PQD solar cells incorporating this novel structure achieved a power conversion efficiency of 14.23%, a significant improvement compared to 12.69% achieved by solar cells with a traditional structure, thus demonstrating the strong potential of this approach for high-performance PQD solar cells.

Iodide Management and Oriented Crystallization Modulation for High-Performance All-Air Processed Perovskite Solar Cells

Halide-related defects at the buried interface not only cause nonradiative recombination, but also seriously impair the long-term stability of perovskite solar cells (PSCs). Herein, a bottom-up, all-in-one modification strategy is proposed by introducing a multisite antioxidant ergothioneine (EGT) at the buried interface to manage iodide ions and manipulate crystallization dynamics. The findings demonstrate that EGT not only passivates uncoordinated Sn4+/Pb2+ defects, but also firmly anchors iodide ions and inhibits their oxidation to I2. Additionally, the modification by EGT enhances the oriented crystallization of perovskite, improves the carrier dynamics, and releases residual stresses. Consequently, the optimized all-air processed device (Rb0.02(FA0.95Cs0.05)0.98PbI2.91Br0.03Cl0.06) achieves a remarkable power conversion efficiency (PCE) of 25.13%, which is among the highest values reported for devices fabricated in air, along with ultrahigh open-circuit voltage (VOC) of 1.191 V and fill factor (FF) of 84.9%. The optimized device without encapsulation exhibits strong humidity, thermal, and operational stability under ISOS protocol. Specifically, the initial efficiency of the device is retained at 90.12% after 1512 h of thermal ageing at 65 °C and 90.14% after 930 h of continuous maximum power point tracking (MPPT) under simulated AM1.5 illumination.

Ligand Engineering Achieves Suppression of Temperature Quenching in Pure Green Perovskite Nanocrystals for Efficient and Thermostable Electroluminescence

Formamidinium lead bromide (FAPbBr3) perovskite nanocrystals (NCs) are promising for display and lighting due to their ultra-pure green emission. However, the thermal quenching will exacerbate their performance degradation in practical applications, which is a common issue for halide perovskites. Here, we reported the heat-resistant FAPbBr3 NCs prepared by a ligand-engineered room-temperature synthesis strategy. An aromatic amine, specifically β-phenylethylamine (PEA) or 3-fluorophenylethylamine (3-F-PEA), was incoporated as the short-chain ligand to expedite the crystallization rate and control the size distribution of FAPbBr3 NCs. Employing this ligand engineering approach, we synthesized high quality FAPbBr3 NCs with uniform grain size and reduced long-chain alkyl ligands, resulting in substantially suppressed thermal quenching and enhanced carrier transportation in the perovskite NCs films. Most notably, more than 90% of the room temperature PL intensity in the 3-F-PEA modified FAPbBr3 NCs film was preserved at 380 K. Consequently, we fabricated ultra-pure green EL devices with a room temperature external quantum efficiency (EQE) as high as 21.9% at the luminance of above 1,000 cd m-2, and demonstrated less than 10% loss in EQE at 343 K. This study introduces a novel room temperature method to synthesize efficient FAPbBr3 NCs with exceptional thermal stability, paving the way for advanced optoelectronic device applications.

The marriage of perovskite nanocrystals with lanthanide‐doped upconversion nanoparticles for advanced optoelectronic applications

The exceptional optoelectronic properties of lead halide perovskite nanocrystals (PeNCs) in the ultraviolet and visible spectral regions have positioned them as a promising class of semiconductor materials for diverse optoelectronic and photovoltaic applications. However, their limited response to near‐infrared (NIR) light due to the intrinsic bandgap (>1.5 eV) has hindered their applications in many advanced technologies. To circumvent this limitation, it is of fundamental significance to integrate PeNCs with lanthanide‐doped upconversion nanoparticles (UCNPs) that are capable of efficiently converting low‐energy NIR photons into high‐energy ultraviolet and visible photons. By leveraging the energy transfer from UCNPs to PeNCs, this synergistic combination can not only expand the NIR responsivity range of PeNCs but also introduce novel emission profiles to upconversion luminescence with multi‐dimensional tunability (e.g., wavelength, lifetime, and polarization) under low‐to‐medium power NIR irradiation, which breaks through the inherent restrictions of individual PeNCs and UCNPs and thereby opens up new opportunities for materials and device engineering. In this review, we focus on the latest advancements in the development of PeNCs‐UCNPs nanocomposites, with an emphasis on the controlled synthesis and optical properties design for advanced optoelectronic applications such as full‐spectrum solar cells, NIR photodetectors, and multilevel anticounterfeiting. Some future efforts and prospects toward this active research field are also envisioned.

Using highly water-stable wool keratin/CsPbBr3 nanocrystals as a portable amine-responsive fluorescent test strip for onsite visual detection of food freshness

Perovskite nanocrystals (PNCs) have emerged as promising candidates for fluorescent probes owing to their outstanding photoelectric properties. However, the conventional CsPbBr3 (CPB) NCs are extremely unstable in water, which has seriously limited their sensing applications in water environment. Herein, we present a powerful ligand engineering strategy for fabricating highly water-stable CPB NCs by using a biopolymer of wool keratin (WK) as the passivator and the polyaryl polymethylene isocyanate (PAPI) as the cross-linking agent. In particular, WK with multi-functional groups can serve as a polydentate ligand to firmly passivate CPB NCs by the ligand exchange process in hot toluene; and then the addition of PAPI can further encapsulate CPB NCs by the crosslinking reaction between PAPI and WK. Consequently, the as-prepared CPB/WK-PAPI NCs can maintain ∼ 80 % of their relative photoluminescence (PL) intensity after 60 days in water, and they still maintain ∼ 40 % of their relative PL intensity even after 512 days in the same environment, which is one of the best water stabilities compared previously reported polymer passivation methods. As a proof-of their application, the portable CPB/WK-PAPI NCs-based test strips are further developed as a fluorescent nanoprobe for real-time and visual monitoring amines and food freshness. Among various amine analytes, the as-prepared test strips exhibit higher sensitivity towards conjugated amines, achieving a remarkable detection limit of 18.3 nM for pyrrole. Our research not only introduces an innovative strategy involving natural biopolymers to enhance the water stability of PNCs, but also highlights the promising potential of PNCs for visually and portably detecting amines and assessing food freshness.

Stabilizing Lead Halide Perovskites via an Organometallic Chemical Bridge for Efficient and Stable Photovoltaics

Defects around the surface and grain boundaries of perovskite films normally cause severe nonradiative recombination and imbalanced charge carrier transport, further limiting both the efficiency and stability of perovskite solar cells (PSCs). To tackle this critical issue, we propose a chemical bridge strategy to reconstruct the interface using organometallic molecules. The commercially available molecule bis(diphenylphosphino)ferrocene (FcP2), with a unique bridge molecular structure, anchors and chelates Pb atoms by forming strong Pb-P bonds and further passivates both surfaces and grain boundaries. Detailed characterization revealed that bridge molecule FcP2 reconstruction can effectively suppress nonradiative recombination, and the electron delocalization properties of the ferrocene core can further achieve more balanced interfacial carrier transport. The resultant N-i-P PSC device outputs close to 25% efficiency together with one of the best reported operational stabilities, maintaining over 95% of the initial efficiency after 1000 h of continuous operation at the maximum power point under 1-sun illumination.

Boosting the Carrier Lifetime and Optical Activity of CsPbX3 Nanocrystals through Aromatic Ligand Passivation

Ligand engineering is crucial for tuning the structural and optoelectronic properties of perovskite nanocrystals (NCs), which also improves their stability. In contrast to the typically used long-chain alkylamine ligands, we successfully introduced an aromatic 1-(p-tolyl)ethylamine (PTEA) ligand to synthesize the CsPbX3 (X = Br or I) NCs. The CsPbI3 and CsPbBr3 NCs demonstrated long carrier lifetimes of ∼877 and 49 ns, respectively, as well as high photoluminescence quantum yields (PLQYs) of ∼99% and 95%, respectively. Furthermore, such NCs realized excellent long-term stability in an ambient atmosphere without obvious degradation over one month. All of these properties were better than the properties of NCs coated with the conventional alkylamine ligands. The high performance of these NCs was discussed with the effective surface passivation by PTEA. Our finding suggests a facile and effective ligand (PTEA) for modulating perovskites, achieving enhancement of both the carrier lifetime and the PLQY.

Multifunctional MOF@COF Nanoparticles Mediated Perovskite Films Management Toward Sustainable Perovskite Solar Cells

Although covalent organic frameworks (COFs) with high π-conjugation have recently exhibited great prospects in perovskite solar cells (PSCs), their further application in PSCs is still hindered by face-to-face stacking and aggregation issues. Herein, metal-organic framework (MOF-808) is selected as an ideal platform for the in situ homogeneous growth of a COF to construct a core-shell MOF@COF nanoparticle, which could effectively inhibit COF stacking and aggregation. The synergistic intrinsic mechanisms induced by the MOF@COF nanoparticles for reinforcing intrinsic stability and mitigating lead leakage in PSCs have been explored. The complementary utilization of π-conjugated skeletons and nanopores could optimize the crystallization of large-grained perovskite films and eliminate defects. The resulting PSCs achieve an impressive power conversion efficiency of 23.61% with superior open circuit voltage (1.20 V) and maintained approximately 90% of the original power conversion efficiency after 2000 h (30-50% RH and 25-30 °C). Benefiting from the synergistic effects of the in situ chemical fixation and adsorption abilities of the MOF@COF nanoparticles, the amount of lead leakage from unpackaged PSCs soaked in water (< 5 ppm) satisfies the laboratory assessment required for the Resource Conservation and Recovery Act Regulation.

Fast Organic Cation Exchange in Colloidal Perovskite Quantum Dots toward Functional Optoelectronic Applications

Colloidal quantum dots with lower surface ligand density are desired for preparing the active layer for photovoltaic, lighting, and other potential optoelectronic applications. In emerging perovskite quantum dots (PQDs), the diffusion of cations is thought to have a high energy barrier, relative to that of halide anions. Herein, we investigate the fast cross cation exchange approach in colloidal lead triiodide PQDs containing methylammonium (MA+) and formamidinium (FA+) organic cations, which exhibits a significantly lower exchange barrier than inorganic cesium (Cs+)-FA+ and Cs+-MA+ systems. First-principles calculations further suggest that the fast internal cation diffusion arises due to a lowering in structural distortions and the consequent decline in attractive cation-cation and cation-anion interactions in the presence of organic cation vacancies in mixed MA+-FA+ PQDs. Combining both experimental and theoretical evidence, we propose a vacancy-assisted exchange model to understand the impact of structural features and intermolecular interaction in PQDs with fewer surface ligands. Finally, for a realistic outcome, the as-prepared mixed-cation PQDs display better photostability and can be directly applied for one-step coated photovoltaic and photodetector devices, achieving a high photovoltaic efficiency of 15.05% using MA0.5FA0.5PbI3 PQDs and more precisely tunable detective spectral response from visible to near-infrared regions.