Prolonged Carrier Lifetime Research Articles

Semi-Transparent, Pixel-Free Upconversion Goggles with Dual Audio-Visual Communication.

The intractable brittleness and opacity of the crystalline semiconductor restrict the prospect of developing low-cost imaging systems. Here, infrared visualization technologies are established with large-area, semi-transparent organic upconversion devices that bring high-resolution invisible images into sight without photolithography. To exploit all photoinduced charge carriers, a monolithic device structure is proposed built on the infrared-selective, single-component charge generation layer of chloroaluminum phthalocyanine (ClAlPc) coupled to two visible light-emitting layers manipulated with unipolar charges. Transient pump-probe spectroscopy reveals that the ClAlPc-based device exhibits an efficient charge dissociation process under forward bias. This process is indicated by the prompt and strong features of electroabsorption screening. Furthermore, by imposing the electric field, the ultrafast excited state dynamic suggests a prolonged charge carrier lifetime from the ClAlPc, which facilitates the charge utilization for upconversion luminance. For the first time, >30% of the infrared photons are utilized without photomultiplication strategies owing to the trivial spectrum overlap between ClAlPc and the emitter. In addition, the device can broadcast the acoustic signal by synchronizing the device frequency with the light source, which enables to operate it in dual audio-visual mode. The work demonstrates the potential of upconversion devices for affordable infrared imaging in wearable electronics.

Electron Transport Layer Engineering Induced Carrier Dynamics Optimization for Efficient Cd-Free Sb2 Se3 Thin-Film Solar Cells.

Antimony selenide (Sb2 Se3 ) is a highly promising photovoltaic material thanks to its outstanding optoelectronic properties, as well as its cost-effective and eco-friendly merits. However, toxic CdS is widely used as an electron transport layer (ETL) in efficient Sb2 Se3 solar cells, which largely limit their development toward market commercialization. Herein, an effective green Cd-free ETL of SnOx is introduced and deposited by atomic layer deposition method. Additionally, an important post-annealing treatment is designed to further optimize the functional layers and the heterojunction interface properties. Such engineering strategy can optimize SnOx ETL with higher nano-crystallinity, higher carrier density, and less defect groups, modify Sb2 Se3 /SnOx heterojunction with better interface performance and much desirable "spike-like" band alignment, and also improve the Sb2 Se3 light absorber layer quality with passivated bulk defects and prolonged carrier lifetime, and therefore to enhance carrier separation and transport while suppressing non-radiative recombination. Finally, the as-fabricated Cd-free Mo/Sb2 Se3 /SnOx /ITO/Ag thin-film solar cell exhibits a stimulating efficiency of 7.39%, contributing a record value for Cd-free substrate structured Sb2 Se3 solar cells reported to date. This work provides a viable strategy for developing and broadening practical applications of environmental-friendly Sb2 Se3 photovoltaic devices.

Quantum Dot Bridges Enabling Highly Efficient Carbon‐Based Hole Transport Material‐Free Perovskite Solar Cells

The realization of improved charge transport with suppressed recombination at the interface of perovskite and carbon electrode is the main key for remarkably increasing the power conversion efficiency of carbon‐based hole transport material (HTM)‐free perovskite solar cells (PSCs). Herein, a strategy that builds a perovskite quantum dot (PQD) interlayer is demonstrated, for the first time, to bridge the perovskite absorber and carbon electrode for solving the interface issue in HTM‐free PSCs. It is found that the introduced PQD interlayer concurrently functions as a morphology changer, a defect passivator, and a photogenerated hole extractor. Compared with the pristine perovskite film, the PQD‐modified perovskite absorber shows increased contact area and high compatibility with carbon electrode, prolonged carrier lifetime, deduced defect density as well as suppressed recombination. These positive effects, combined with a heterostructure created by perovskite bulks and PQDs facilitating hole transport at the interface, enable an improvement in device efficiency from 16.71% to 17.93%.

Enhanced Photoluminescence and Prolonged Carrier Lifetime through Laser Radiation Hardening and Self-Healing in Aged MAPbBr3 Perovskites Encapsulated in NiO Nanotubes.

Organic-inorganic perovskites hold great promise as optoelectronic semiconductors for pure color light emitting and photovoltaic devices. However, challenges persist regarding their photostability and chemical stability, which limit their extensive applications. This paper investigates the laser radiation hardening and self-healing-induced properties of aged MAPbBr3 perovskites encapsulated in NiO nanotubes (MAPbBr3@NiO) using photoluminescence (PL) and fluorescence lifetime imaging (FLIM). After deliberately subjecting the MAPbBr3@ NiO to atmospheric conditions for two years, the sample remains remarkably stable. It exhibits no changes in PL wavelength during UV laser irradiation and self-healing. Furthermore, exposure to UV light at 375 nm enhances the PL of the self-healed MAPbBr3@NiO. FLIM analysis sheds light on the mechanism behind photodegradation, self-healing, and PL enhancement. The results indicate the involvement of many carrier-trapping states with low lifetime events and an increase in peak lifetime after self-healing. The formation of trapping states at the perovskite/nanotube interface is discussed and tested. This study provides new insights into the dynamics of photo-carriers during photodegradation and self-healing in organic-inorganic perovskites.

Charge Carrier Dynamics in Non-Fullerene Acceptor-Based Organic Solar Cells: Investigating the Influence of Processing Additives Using Transient Absorption Spectroscopy.

In this study, we present a comprehensive investigation into the charge generation mechanism in bulk-heterojunction organic solar cells employing non-fullerene acceptors (NFAs) both with and without the presence of processing additives. While photovoltaic devices based on Y6 or BTP-eC9 have shown remarkable power conversion efficiencies, the underlying charge generation mechanism in polymer:NFA blends remains poorly understood. To shed light on this, we employ transient absorption (TA) spectroscopy to elucidate the charge transfer pathway within a blend of the donor polymer PM6 and NFAs. Interestingly, the charge carrier lifetimes of neat Y6 and BTP-eC9 are comparable, both reaching up to 20 ns. However, the PM6:BTP-eC9 blend exhibits substantially higher charge carrier generation and a longer carrier lifetime compared to PM6:Y6 blend films, leading to superior performance. By comparing TA data obtained from PM6:Y6 or PM6:BTP-eC9 blend films with and without processing additives, we observe significantly enhanced charge carrier generation and prolonged charge carrier lifetimes in the presence of these additives. These findings underscore the potential of manipulating excited species as a promising avenue for further enhancing the performance of organic solar cells. Moreover, this understanding contributes to the advancement of NFA-based systems and the optimization of charge transfer processes in polymer:NFA blends.

Spin selection in atomic-level chiral metal oxide for photocatalysis

The spin degree of freedom is an important and intrinsic parameter in boosting carrier dynamics and surface reaction kinetics of photocatalysis. Here we show that chiral structure in ZnO can induce spin selectivity effect to promote photocatalytic performance. The ZnO crystals synthesized using chiral methionine molecules as symmetry-breaking agents show hierarchical chirality. Magnetic circular dichroism spectroscopic and magnetic conductive-probe atomic force microscopic measurements demonstrate that chiral structure acts as spin filters and induces spin polarization in photoinduced carriers. The polarized carriers not only possess the prolonged carrier lifetime, but also increase the triplet species instead of singlet byproducts during reaction. Accordingly, the left- and right-hand chiral ZnO exhibit 2.0- and 1.9-times higher activity in photocatalytic O2 production and 2.5- and 2.0-times higher activities in contaminant photodegradation, respectively, compared with achiral ZnO. This work provides a feasible strategy to manipulate the spin properties in metal oxides for electron spin-related redox catalysis.

Reversible and Irreversible Layer Edge Relaxation in Laser‐Radiation‐Hardened 2D Organic–Inorganic Perovskite Crystals

The layer edge states or low energy state (LES) in 2D hybrid organic–inorganic perovskites demonstrate a prolonged carrier lifetime for better performance of optoelectronic devices. However, the fundamental understanding of LES in 2D perovskites is still inconclusive. Herein, a photoluminescence (PL) study of LES in 2D Ruddlesden–Popper perovskites is presented with n = 2 and n = 3 from their cleaved cross sections that are more stable than the natural edge. The PL measurements clearly observe reversible, and irreversible surface relaxations (case I and case II) in three laser intensity ranges, further supported by a PL excitation cycle from low to high laser intensity, and vice versa. The PL wavelength of LES is tunable with laser intensity and blueshifts with increasing laser intensity during irreversible surface relaxation process (case I). Fluorescence lifetime imaging (FLIM) shows that the LES has a longer lifetime than the band‐edge emission in the sample without a photodegradation, while the BE lifetime becomes relatively longer in the area with a photodegradation. The presented laser tunable LES and the related irreversible relaxation process provide a new insight that can help improve the photostability in 2D perovskites and understand roles of LESs in optoelectronic device performance.

Efficient Liquid–Solid Coregulation Engineering in Mixed‐Cation Lead Mixed‐Halide Perovskite for Photovoltaic Performance Improvement

Mixed‐cation lead mixed‐halide perovskite have attracted extensive attention due to their application potential in tandem devices and favorable stability. However, the crystallization of mixed‐component perovskite usually suffers from more complicated phase‐transition processes, making it difficult to prepare high‐quality perovskite films. Herein, it is demonstrated that rhodamine 110 chloride (RC110) additive, a commonly used fluorescent dye, plays significant roles in improving the performance of perovskite solar cells (PSCs). It is shown that the defects can be remarkably reduced by interactions between the defects and the functional groups, the interaction between the RC110 and halogen ions in precursor solution can exert significant effects on the coordination level of lead–halogen octahedral frameworks, and thereby augments the colloidal size in the precursor solution. Leveraging these benefits, the liquid–solid coregulation engineering endows high‐quality perovskite films with enhanced crystallinity, lower defects density, reduced nonradiative recombination, and prolonged carrier lifetime. Consequently, the RC110‐treated planar devices deliver a champion efficiency of 21.02% with negligible hysteresis and exhibit excellent stability. Briefly, this defect passivation strategy based on colloidal coordination engineering provides a novel and feasible route to promote the potential commercialization of PSCs.

Comparison study of the structure, dielectric function, and two-photon absorption cross-section of BiOI and Ag/BiOI nanomaterials

In this research, the interesting methods including X-ray diffraction (XRD) pattern, Field Emission Scanning Electron Microscopy (FESEM) images, energy dispersive X-ray (EDX), UV–Vis spectroscopy, Diffuse reflectance (DRS) spectrum, KK method, and Z-scan measurements were employed for characterizations of prepared BiOI and Ag/BiOI nanomaterials. The optical indices such as n, k, and ε1 and ε2 were assessed based on reflectance spectra data and the Kramers-Kronig (KK) method. Furthermore, the nonlinear optical (NLO) properties of prepared BiOI and Ag/BiOI nanomaterials in different Ag precents were examined through the Z-scan method using the laser beam at 532 nm wavelength. The two-photon absorption (TPA) and self-focusing performance are revealed by the prepared nanomaterials. Adding Ag into BiOI structures, significantly increases the TPA cross-section, σ2 which reaches up to 1.14578 × 10−21 cm4/W for the sample of S3. One of the significant factors that affected the improvement of the optical nonlinearity properties of Ag/BiOI and over BiOI was ascribed to the combined consequence of Ag's localized surface plasmon resonance (LSPR) phenomena, resulting in improved light absorption intensity coupling interaction, significant photo-produced electron-hole separability, and prolonged carrier lifetime.

A unique and well-designed 2D graphitic carbon nitride with sponge-like architecture for enhanced visible-light photocatalytic activity

A unique and well-designed 2D graphitic carbon nitride (g-CN) with sponge-like architecture has been successfully synthesized by engineering supramolecular self-assembly and well-organized SiO2 nanoparticles. The resulting material showed great optical and textural characteristics with plenty of open and uniform pores, which are very helpful whether for multiple light scattering or mass transfer. The formation of boosted delocalized π-conjugated electrons at the molecular level and condensed heptazine building blocks result in enhanced carrier density and charge transfer dynamics. Optical emission spectroscopy and time‐resolved fluorescence lifetime (TRPL) strongly confirmed the enhancement of light harvesting and prolonged charge carrier lifetime. The optimized sample exhibited a degradation performance of 95% of bisphenol A (BPA, 10 mg L–1) after 60 min under visible–light irradiation at pH = 5. All the scavenging experiments, probing experiments as well as electron paramagnetic resonance (EPR) confirm that •O2– is the dominant reactive species that fragments bisphenol A. Interestingly, density functional theory (DFT) calculations unveil that the BPA interaction with a modified g-CN containing porous structure is energetically more favorable than non-porous pure g-CN. Moreover, the toxicity assessment showed that the final degradation products were placed in the non-harmful category based on acute and chronic toxicity. This study presents a promising strategy to modify the g-CN properties and provides an efficient technique for boosting its visible–light photocatalytic activity.

Effective growth strategy of colloidal quantum dots with low defects and high brightness

Quantum dots (QDs) with an alloy shell (CdSe@ZnS/ZnS) are one of the most promising emitters for optoelectronic devices for their superior properties such as narrow full width at half maximum (FWHM), high color purity and tunable wavelength. However, the presence of lattice stresses during the internal growth of quantum dots can cause severe exciton bursts. Optimizing the ramp-up process during the core growth of quantum dots and rising the temperature when cladding with ZnS shells is an effective strategy for obtaining high-quality quantum dots. Besides, the stability of quantum dots is further modified by using 1-Octanethiol (OT) as ligands. Detailed analyses of the morphology, colloidal stability, and luminescence performance of QDs were represented. Finally, green CdSe@ZnS/ZnS QLEDs with prolonged carrier lifetimes and less defect state densities achieved peak luminescence at 361850 cd/m2 with a current efficiency (CE) of 33 cd/A. This work provides a better understanding of the relationship between defect state density and the performance of quantum dots for designing and fabricating high-performance light-emitting diodes.

Molecule Passivation of Grain Boundaries for Ultra‐Stable Perovskite Solar Cells

Perovskite solar cells have become stars in photovoltaics due to their rapidly increased efficiency. However, their stability is still below par due to moisture permeation from grain boundaries and defects. To conquer both problems at once, a passivation agent 3,4,5,6‐tetrafluorophthalicacid (TFPA) is rationally designed to heal both for not only improved cell efficiency but also better stability. It is found that the TFPA is prone to distribute along grain boundaries and has little influence within the bulk of the perovskite film. In addition, it appears that the TFPA helps to reduce the film roughness, to adjust the energy level, to facilitate hole transporting from perovskite to spiro‐OMeTAD, and to increase the hydrophobicity of the perovskite film, as it is demonstrated by the inhibited nonradiative recombination and prolonged carrier lifetime. Owing to strong interactions between F, ‐COOH, and Pb, the device with TFPA shows outstanding efficiency and stability. A perovskite solar cell with TFPA modification delivers a champion efficiency of 23.70% and a significantly enhanced stability that the device maintains 90% of its initial efficiency after 5200 h, among the best ambient stability. Herein, an effective strategy of grain boundary passivation is provided to improve the stability of perovskite solar cells.

A novel Zn0.5Cd0.5S/WO3·H2O S-scheme heterostructures with one-pot synthesis for significant photodegradation of toxic Cr (VI) and organic RhB pollutants: Kinetics, degradation mechanism and photocatalytic evaluation

The artificial-photosynthetic semiconductor composites have attracted tremendous attention with respect to their enhanced photocatalytic properties. Herein, we reported the facile synthesis of Zn0.5Cd0.5S/WO3·H2O S-scheme photocatalyst via one-pot in situ hydrothermal strategy. Density Functional Theory (DFT) calculation was employed to reveal the S-scheme photogenerated electron transfer mechanism, and the subsequent experimental characterization further illustrated the path for electron-hole transfer and separation under the effect of S-scheme heterojunction. The mass of WO3·H2O accounted for Zn0.5Cd0.5S/WO3·H2O 48 wt% (ZCSW48) was the best high-efficiency S-scheme photocatalyst displayed significant photocatalytic properties on pollution degradation, in detail, with the Cr (VI) photoreduction rate of 2.27 μmol·s−1·g−1cat. and the Rhodamine B (RhB) photooxidation rate of 0.38 μmol·min−1·g−1cat., respectively. The designed Zn0.5Cd0.5S/WO3·H2O photocatalysts have integrated with the three aspects of photocatalytic efficiencies including the visible light response, prolonged photogenerated carrier lifetime and the sufficient surface active sites due to amount of surface defects, therefore, this work provides more insights into the utilization of green energy for environmental treatment by artificial structured semiconductors.

D 6 h Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

<i>D</i> ^{6 <i>h</i>} Symmetric Radical Donor–Acceptor Nanographene Modulated Interfacial Carrier Transfer for High-Performance Perovskite Solar Cells

Engineered disorder in CO2 photocatalysis

Light harvesting, separation of charge carriers, and surface reactions are three fundamental steps that are essential for an efficient photocatalyst. Here we show that these steps in the TiO2 can be boosted simultaneously by disorder engineering. A solid-state reduction reaction between sodium and TiO2 forms a core-shell c-TiO2@a-TiO2-x(OH)y heterostructure, comprised of HO-Ti-[O]-Ti surface frustrated Lewis pairs (SFLPs) embedded in an amorphous shell surrounding a crystalline core, which enables a new genre of chemical reactivity. Specifically, these SFLPs heterolytically dissociate dihydrogen at room temperature to form charge-balancing protonated hydroxyl groups and hydrides at unsaturated titanium surface sites, which display high reactivity towards CO2 reduction. This crystalline-amorphous heterostructure also boosts light absorption, charge carrier separation and transfer to SFLPs, while prolonged carrier lifetimes and photothermal heat generation further enhance reactivity. The collective results of this study motivate a general approach for catalytically generating sustainable chemicals and fuels through engineered disorder in heterogeneous CO2 photocatalysts.

Vacancy-Regulated Charge Carrier Dynamics and Suppressed Nonradiative Recombination in Two-Dimensional ReX2 (X = S, Se).

Point defects in semiconductors usually act as nonradiative charge carrier recombination centers, which severely limit the performance of optoelectronic devices. In this work, by combining time-domain density functional theory with nonadiabatic molecular dynamics simulations, we demonstrate suppressed nonradiative charge carrier recombination and prolonged carrier lifetime in two-dimensional (2D) ReX2 (X = S, Se) with S/Se vacancies. In particular, a S vacancy introduces a shallow hole trap state in ReS2, while a Se vacancy introduces both hole and electron trap states in ReSe2. Photoexcited electrons and holes can be rapidly captured by these defect states, while the release process is slow, which contributes to an elongated photocarrier lifetime. The suppressed charge carrier recombination lies in the vacancy-induced low-frequency phonon modes that weaken electron-phonon coupling, as well as the reduced overlap between electron and hole wave functions that decreases nonadiabatic coupling. This work provides physical insights into the charge carrier dynamics of 2D ReX2, which may stimulate considerable interest in using defect engineering for future optoelectronic nanodevices.

Efficient Tin (II) Fluoride‐Free Formamidinium Tin Triiodide Perovskite Solar Cells via Composition and Additive Engineering

Tin halide perovskite solar cells (TPSCs) have attracted extensive attention because of their low toxicity and high theoretical efficiency. However, rapid crystallization, rich defects, and easy oxidation of tin‐based perovskite films seriously restrict solar cell performance. Herein, a composition and additive engineering solution by removing commonly used tin fluoride additive from formamidinium tin triiodide perovskite precursors and replacing it with excess tin (II) iodide and ethylenediamine dihydroiodide (EDAI2) is adopted. The presence of EDAI2 and excess SnI2 and the absence of SnF2 enable tin‐based perovskite films with greatly improved morphology, enhanced crystalline quality, boosted optical properties, and prolonged carrier lifetime. Therefore, the SnF2‐free non‐stoichiometric TPSCs employing the EDAI2 additive and excess SnI2 have increased built‐in potential, lowered dark currents, and reduced carrier recombination. The resulting SnF2‐free and SnI2‐rich TPSCs with EDAI2 addition realize a steady‐state efficiency of 10.0%, which is one of the highest power conversion efficiencies among the SnF2‐free TPSCs, along with considerably improved light stability. This work highlights the crucial roles of additives in TPSCs and provides an effective strategy to fabricate efficient and stable low‐toxic lead‐free perovskite solar cells.

Simultaneous Lattice Engineering and Defect Control via Cadmium Incorporation for High-Performance Inorganic Perovskite Solar Cells.

Doping of all-inorganic lead halide perovskites to enhance their photovoltaic performance and stability has been reported to be effective. Up to now most studies have focused on the doping of elements in to the perovskite lattice. However, most of them cannot be doped into the perovskite lattice and the roles of these dopants are still controversial. Herein,the authors introduce CdI2 as an additive into CsPbI3-x Brx and use it as active layer to fabricate high-performance inorganic perovskite solar cells (PSCs). Cd with a smaller radius than Pb can partially substitute Pb in the perovskite lattice by up to 2 mol%. Meanwhile, the remaining Cd stays on the surface and grain boundaries (GB) of the perovskite film in the form of Cs2 CdI4-x Br-x , which is found to reduce non-radiative recombination. These effects result in prolonged charge carrier lifetime, suppressed defect formation, decreased GBs, and an upward shift of energybands in the Cd-containing film. A champion efficiency of 20.8% is achieved for Cd-incorporated PSCs, together with improved device ambient stability. This work highlights the importance of simultaneous lattice engineering, defectcontrol and atomic-level characterization in achieving high-performance inorganic PSCs with well-defined structure-property relationships.

Efficient Inverted Perovskite Solar Cells with a Low‐Dimensional Halide/Perovskite Heterostructure

AbstractThe photovoltaic performance of inverted (positive‐intrinsic‐negative) perovskite solar cells (PSCs) is predominantly limited by interfacial recombination loss. Here, by constructing a low‐dimensional halide/perovskite heterostructure, non‐radiative recombination pathways at the perovskite/C60 contact are effectively eliminated and a voltage loss of only 370 mV is achieved in inverted PSCs. Through molecular engineering of the organic spacer, a strong electronic coupling is enabled at the heterointerface, which effectively shifts the gap states out of the bandgap and leads to a prolonged carrier lifetime of 4.28 µs. Our strategy enables a power conversion efficiency of 24.09% (certified 23.54%) for inverted PSCs with an open‐circuit voltage of 1204 mV, and an efficiency of 21.89% (certified 21.48%) for centimeter‐scale cells. The devices retain 92% of the initial efficiency after 85 °C thermal aging for over 1400 h, and 95% of the initial efficiency after 1008 h of maximum power point operation under AM1.5G illumination in air.

All-in-one additive enables defect passivated, crystallization modulated and moisture resisted perovskite films toward efficient solar cells

The high-quality perovskite film with low trap densities and large grains is a prerequisite for achieving high-performance and stable perovskite solar cells (PSCs). It is desirable to simultaneously realize the defect passivation and crystallization control of perovskite films. Here, an all-in-one additive, named 2-[N,N-bi(trifluoromethylsulfonyl)amino]pyridine (2-BTFSIP), is introduced into the perovskite layer to address this issue. It is demonstrated that the sulfonyl group and pyridine nitrogen cooperatively passivate the deep-level traps (Pb0 cluster and under-coordinated Pb2+ ions), while the trifluoromethyl group suppresses the evaporation of organic cations as well as improves the hydrophobicity of perovskite films. In addition, crystallization control is also realized by the synergetic effect of multiple groups to obtain a larger crystal size. It is revealed that reduced defect densities, suppressed non-radiative recombination and prolonged carrier lifetimes are achieved. As a result, MAPbI3 and FAPbI3 devices passivated by the 2-BTFSIP molecule yield the champion power conversion efficiency (PCE) of 21.96% and 22.90% with negligible hysteresis, respectively. Meanwhile, 2-BTFSIP-modified MAPbI3 devices maintain over 90% of its original PCE as long as for 6000 h storage. Hence, this work provides a new perspective for designing effective multifunctional additives to remarkably improve PCE and stability of PSCs.