Carrier Generation Research Articles

Mechanically mediated bulk atom transfer radical polymerization enabled by high‐performance piezoelectric Bi0.5Na0.5TiO3

AbstractThis study presents the successful mechanically mediated bulk atom transfer radical polymerization (mechano‐ATRP) of methyl acrylate (MA) using the high‐performance piezoelectric material Bi0.5Na0.5TiO3 (BNT) under ultrasonic conditions. Compared to the widely used BaTiO3 in mechano‐ATRP, BNT demonstrates superior piezoelectric performance, enhancing carrier generation, separation, and interfacial transfer. The strong interaction between BNT and Cu catalysts facilitates the rapid capture of mechano‐induced electrons, leading to the formation of CuI/L and efficient polymerization initiation. Factors such as piezoelectric material loading, Cu catalyst loading, targeted degrees of polymerization, and sonication power were systematically evaluated. The living nature of ATRP was confirmed by polymers with predetermined molecular weights and low dispersitis (<1.2). This work broadens the application of ATRP and offers valuable insights into the design of piezoelectric catalytic materials for mechano‐ATRP.

A simple method to find temporal overlap between THz and x-ray pulses using x-ray-induced carrier dynamics in semiconductors

X-ray-induced carrier dynamics in silicon and gallium arsenide were investigated through intensity variations of transmitted terahertz (THz) pulses in the pico- to microsecond timescale with x-ray free-electron laser and synchrotron radiation. We observed a steep reduction in THz transmission with a picosecond scale due to the x-ray-induced carrier generation, followed by a recovery on a nano- to microsecond scale caused by the recombination of carriers. The rapid response in the former process is applicable to a direct determination of temporal overlap between THz and x-ray pulses for THz pump–x-ray probe experiments with an accuracy of a few picoseconds.

Investigating the contribution effect of carrier generation rates to enhance optical absorption in single /a-Si/AuNPs/, /AuNPs@TiO2/ plasmonic structures and their dual combined /a-Si/AuNPs/AuNPs@TiO2/ plasmonic structure for possible application in solid-state plasmonic solar cells

Investigating the contribution effect of carrier generation rates to enhance optical absorption in single /a-Si/AuNPs/, /AuNPs@TiO2/ plasmonic structures and their dual combined /a-Si/AuNPs/AuNPs@TiO2/ plasmonic structure for possible application in solid-state plasmonic solar cells

Observation of ultraviolet photothermoelectric bipolar impulse in gallium-based heterostructure nanowires

The incorporation of thermal dynamics alongside conventional optoelectronic principles holds immense promise for advancing technology. Here, we introduce a GaON/GaN heterostructure-nanowire ultraviolet electrochemical cell of observing a photothermoelectric bipolar impulse characteristic. By leveraging the distinct thermoelectric properties of GaON/GaN, rapid generation of hot carriers establishes bidirectional instantaneous gradients in concentration and temperature within the nanoscale heterostructure via light on/off modulation. The thermoelectromotive force induced by these gradients, combined with the type-II heterojunction band structure, facilitates carrier transport, resulting in transient bidirectional photothermal currents. The device achieves exceptional responsivity (17.1 mA/W) and remarkably fast speed (8.8 ms) at 0 V, surpassing existing semiconductor electrochemical cells. This bipolar ultraviolet impulse detection mode harnesses light-induced heat for electricity generation, enabling innovative bidirectional encryption communication capabilities. Anticipated applications encompass future sensing, switchable light imaging, and energy conversion systems, thereby laying a foundation for diverse optoelectronic technological advancements.

Synergistic plasmon resonance hybridization of iron‐dispersed MoO3−x/MXene for enhanced nitrogen photothermal reduction

AbstractPlasmonic photochemical N2 fixation has received widespread attention owing to the attractive plasmonic enhancement effects in improving solar‐to‐NH3 conversion efficiency. However, the weak N2 adsorption affinity in metallic plasmonic photocatalysts and insurmountable interfacial barriers in metal–semiconductor plasmonic photocatalysts lead to rapid charge carrier recombination instead of participating in N2‐to‐NH3 conversion. Herein, a photothermal catalyst Fe‐dispersed MoO3−x/MXene with synergistic plasmon resonance hybridization structure is fabricated for photothermal N2 fixation. The hybrid plasmon resonance effects derived from MXene and MoO3−x induce a strong optical response across the ultraviolet–visible‐near‐infrared range and generation of energetic charge carriers, and the induced photothermal effect further accelerates electron extraction, transport, and surface reaction kinetics. Moreover, the abundant oxygen vacancies and Fe sites can intensify the N2 adsorption and donate the energetic electrons into the anti‐bonding system for the stimulative NH coupling process. A high NH3 formation rate of 87.1 μmol g−1 h−1 is achieved under solar‐level illumination.

Scrutinizing the untapped potential of emerging ABSe3 (A = Ca, Ba; B = Zr, Hf) chalcogenide perovskites solar cells

ABS3chalcogenide perovskites (CPs) are emerging as promising alternatives to lead halide perovskites due to their unique properties. However, their bandgap exceeds the Shockley-Queisser limit. By substituting S with Se, the bandgap is significantly reduced, shifting it from the visible into the near-infrared region. Hence, we have investigated the potential of Se-based absorbers with device structure FTO/TiO2/ABSe3 (A = Ca, Ba; B = Zr, Hf)/NiO/Au using SCAPS-1D. We analyzed the critical parameters impacting each layer of the solar cell. Notably, we achieved an enhanced light absorption (~ 26.5%) at an optimal absorber thickness (500 nm), intensifying carrier generation. Additionally, we observed an increase in VOC (1.03 V) due to improved quasi-Fermi level splitting and a reduction in energy loss (0.45 V) across all solar cells with an optimal absorber carrier concentration (1016 cm−3). Overall, the optimization resulted in improvements in PCE by the difference of 20.14%, 20.44%, 14.33%, and 14.56% for CaZrSe3, BaZrSe3, CaHfSe3, and BaHfSe3 solar cells, respectively. The maximum PCE of over 30% was attained for both CaZrSe3and BaZrSe3 solar cells, attributed to their narrow bandgap, enhanced light absorption (53.60%), high JSC (29 mA/cm2), and elevated generation rate of 1.19 × 1022 cm−2s−1. Thus, these significant outcomes highlight the potential of these absorbers for fabricating high-efficiency CP solar cells.

Hierarchically Enhanced Plasmonic Absorber with Abundant Nanomirrors for Effective Photoelectrochemical Performance

The synergistic combination of plasmonic metals and semiconductors demonstrates marvelous potential for nanocomposite design, particularly in enhancing photoelectrochemical performance through rich interfacial modifications and component properties adjustments. In terms of it, nanocomplexes of metal/insulator or semiconductor/metal have emerged heatedly, commonly depicted as nanomirror structures. In this work, a sandwiched nanomirror structure comprising a core Ag nanorods, a TiO2 middle nanogap, and dual types of Au and Ag particles outermost is presented, putting forward a novel design idea of rolling the planar complex up to amplify the potential interaction systems. The TiO2 middle layer enables the intrinsic generation of charge carriers upon light exposure, while the established heterojunctions promote their efficient separation. Additionally, both the inner Ag NRs and outer metal nanoparticles exhibit localized surface plasma resonance effects to realize enhancement of electric fields, where plasmonic coupling between them generates field hotspots within TiO2 layer, thereby expanding light absorption range and enhancing light capture intensity. Beyond, hot electrons from plasmonic metals traverse Schottky barriers into TiO2 to participate in further reactions, all of which contribute to heightened PEC performance of the nanostructure. In this work, the path is paved for innovative nanostructure design integrating plasmonic metals with semiconductors, offering promising implications for energy‐related applications.

First-Principles Study on the Electronic Structure and Optical Properties of BiOIO3 Doped with As, Se, and Te

This study calculates the electronic structure and optical properties of intrinsic BiOIO3 and X-BiOIO3 (X = As, Se, or Te) using PBE (Perdew–Burke–Ernzerhof) and MBJ (Modified Becke–Johnson) functionals based on density functional theory, with MBJ showing better correlation with experimental values. The X-BiOIO3 systems exhibit relative stability under MBJ potential and show crystal lattice distortion compared to intrinsic BiOIO3, creating localized potential differences that enhance polarization and adjust the bandgap. Doping reduces the bandwidth and increases energy level density, promoting electron transitions. Consequently, based on the computational results presented in this paper, it can be inferred that both BiOIO3 and X-BiOIO3 facilitate water hydrolysis and oxygen generation due to their favorable energy band positions. Notably, Se-BiOIO3 exhibits the highest visible light absorption capacity, which may enhance photocatalytic efficiency by strengthening the built-in electric field and promoting charge carrier generation.

Self-Powered Filterless Narrowband UV Photodetection Triggered by Asymmetric Charge Carrier Generation in a Wide-Bandgap Halide Perovskite Ferroelectric.

Narrowband photodetection with selective light detection in ultraviolet (UV) range is particularly pronounced in specialized such as targeted wavelength imaging and UV-phototherapy. In contrast to conventional strategies, ferroelectric materials with pronounced bulk photovoltaic effect (BPVE) provide a novel asymmetric carrier generation concept for achieving filterless spectrally selective photodetection. Herein, for the first time, the realization of self-powered filterless narrowband UV photodetection is demonstrated in bulk single crystals of a newly developed halide perovskite ferroelectric, 2FEA2EA2Pb2Cl10 (2FEEPC), which exhibits a wide bandgap of 3.36eV and a remarkable spontaneous polarization (≈3.5 µCcm-2). Benefiting from the strongly distorted inorganic framework with asymmetric delocalized electronic states, 2FEEPC demonstrates a highly wavelength-dependent BPVE along the polar direction, showing a high narrowband detecting performance with a response peak at UV wavelength of 355nm and a full-width-at-half-maximum (FWHM) of ≈15nm. More interestingly, the ferro-pyro-phototronic effect of 2FEEPC endows a colossal gain of up to 600% for photopyroelectric current. This work presents an unprecedented approach to achieve self-powered filterless narrowband photodetection, thereby shedding light on the development of photosensitive ferroelectrics for spectrally photoelectric applications.

Multiple Exciton Generation on Doped Wide-Band Semiconductor Photoanode with Hierarchical Quantum Structure.

The multiple exciton generation (MEG) effect, which produces multiple photo-generated charge carriers from a single high-energy photon absorption by a semiconductor with a narrow bandgap, has the potential to revolutionize photovoltaic, photoelectric detection, and other technologies. Here, this work finds that the surface carbon-modified wide-bandgap photoanode with hierarchical quantum structure can drive a photoelectrochemical reaction with a quantum efficiency exceeding 145% by the first time. More studies reveal that the presence of the MEG effect in the MEG-CdS photoanode is attributed to the formation of high-quality surface C-modified CdS quantum nanosheets on CdS bulk film by in situ, this hierarchical quantum structure leads to quantum confinement effects that increase effective Coulomb interaction for driving MEG and decrease competition for thermal exciton cooling. The acceptor level introduced by carbon reduces the MEG threshold (approximately twice the energy level difference) and collaborates with the built-in electric field of the C-CdS/bulk-CdS homojunction to enable the effective generation and separation of photo-generated charge carriers. The internal quantum efficiency of the MEG-CdS photoanode reaches up to a recording value of 145%, providing a novel perspective on the contribution of surface-modified wide-band semiconductors and their quantum effects in the application of MEG.

Multiple Carrier Generation at an Exceptionally Low Energy Threshold.

Multiple carrier generation (MCG), a process wherein two or more carriers are generated from a single high-energy absorbed photon, holds immense promise for quantum sensing, metrology, low-threshold lasers, and photovoltaics. Despite its potential, MCG has faced obstacles such as low efficiency and a high threshold photon energy at least twice the band gap (2E_{g}) of the semiconductor, limiting its application only to a class of materials with low E_{g}. Here, we present a new approach that overcomes this limitation by leveraging carrier-donor scattering to excite secondary electrons from donor states strategically positioned below the conduction band. Our method relies on strong Coulomb interaction, reduced dielectric screening, slow hot carrier cooling, and strictly follows the energy conservation rules. We experimentally demonstrated this idea in a model system of monolayer (1L) MoS_{2} by exploiting electron-donating chalcogen vacancy states. We observed an exceptionally low MCG threshold of ∼1.12E_{g} for the first time in 1L MoS_{2}. Remarkably, the quantum yield can be further increased to >3 by increasing the photon energy to 1.65E_{g}, representing a substantial advancement over existing methods. Our findings extend the horizon of MCG into next-generation high-performance optoelectronic devices with an on-demand operating spectral range spanning from infrared to ultraviolet.

Revealing Intrinsic Free Charge Generation: Promoting the Construction of Over 19% Efficient Planar p‐n Heterojunction Organic Solar Cells

AbstractDue to high binding energy and extremely short diffusion distance of Frenkel excitons in common organic semiconductors at early stage, mechanism of interface charge transfer‐mediated free carrier generation has dominated the development of bulk heterojunction (BHJ) organic solar cells (OSCs). However, considering the advancements in materials and device performance, it is necessary to reexamine the photoelectric conversion in current‐stage efficient OSCs. Here, we propose that the conjugated materials with specific three‐dimensional donor‐acceptor conjugated packing potentially exhibit distinctive charge photogeneration mechanism, which spontaneously split Wannier‐Mott excitons to free carriers in pure phases. Subsequently, the pure planar p‐n heterojunction (PHJ) OSCs based on green orthogonal solvents were prepared and exhibited comparable even greater performance to that of BHJ OSCs. More interestingly, by introducing PVDF‐TrFE as intrinsic region to regulate built‐in electric field of the device, the planar p‐i‐n PHJ OSCs achieved much higher efficiency (>18%) and stability. Moreover, a prominent efficiency of over 19% has been obtained via ternary optimization, which is the new efficiency record for PHJ OSCs up to date. This study points towards the distinguishing intrinsic free charge generation mechanism, opens up a new avenue for OSCs to collectively realize high‐efficiency, long‐term duration, and simplified device engineering for future commercialization.

Enhancement of Photocatalytic Activity in BiFeO3 Nanoparticles through Electrical Polarization

This study investigates the enhancement of photocatalytic properties in BiFeO3 nanoparticles through an additional electrical polarization (poling) pretreatment process. BiFeO3, a promising multiferroic material with a narrow bandgap of ≈2. 12 eV, is well‐suited forvisible light‐driven photocatalysis. However, its photocatalytic efficiency isoften limited by insufficient photogenerated charge availability. To address this, a poling process was employed to align the ferroelectric domains within BiFeO3 nanoparticles, improving charge separation and enhancing photocatalytic activity. The findings reveal that the poling process preserves the intrinsic bandgap of BiFeO3, maintaining its visible light absorption capability. Steady‐state photoluminescence spectroscopy shows a marked increase in the intensity in poling‐treated samples, indicating enhanced charge carrier generation. Photo degradation experiments using Indigo dye as a model pollutant demonstrate that poling‐treated BiFeO3 achieves a remarkable photodegradation efficiency of 99%, compared to 56% for untreated BiFeO3. Additionally, the poling‐treated BiFeO3 retains 65% of its initial efficiency after four cycles, highlighting its durability for sustained environmental applications. This study underscores the effectiveness of poling in enhancing the photocatalytic performance of BiFeO3 nanoparticles, providing valuable insights into the development of efficient photocatalysts via domain engineering for environmental purification technologies.

Chalcogenide perovskites: enticing prospects across a wide range of compositions and optoelectronic properties for stable photodetector devices

Abstract Photodetectors are indispensable components of many modern light sensing and imaging devices, converting photon energy into processable electrical signal through absorption, carrier generation and extraction using semiconducting thin films with appropriate optoelectronic properties. Recently, metal halide perovskites have demonstrated groundbreaking photodetector performance due to their exceptional properties originating from their perovskite structure. However, toxicity and stability remain challenges for their large-scale applications. Inspired by the perovskite structure, intense investigation in search of highly stable, non-toxic and earth abundant materials with superior optoelectronic features has led to the discovery of chalcogenide perovskites (CPs). These are unconventional semiconductors with the formula ABX3, where A and B are cations and X is a chalcogen, which covers the compounds with the corner sharing perovskite structures of type II-IV- VI3 compounds (II = Ba, Sr, Ca, Eu; IV = Zr, Hf; VI = S, Se) and III1-III2-VI3 compounds (III1 and III2 = Lanthanides, Y, Sc; VI = S, Se). The increased coordination and ionicity in these compounds contribute to their excellent charge transport properties and exceptionally high optical absorption coefficient (> 105 cm−1). The present review encompasses theoretical analysis that provides electronic band structures and the orbital contributions that support the excellent optoelectronic properties. Furthermore, the challenging thin film deposition, characterizations, and their application in photodetection focusing on BaZrS3-which is the most studied one, are ascribed. Additionally, we suggest prospects that can bring out the true potential of these materials in photodetection and photovoltaics.

Revealing Intrinsic Free Charge Generation: Promoting the Construction of Over 19% Efficient Planar p-n Heterojunction Organic Solar Cells.

Due to high binding energy and extremely short diffusion distance of Frenkel excitons in common organic semiconductors at early stage, mechanism of interface charge transfer-mediated free carrier generation has dominated the development of bulk heterojunction (BHJ) organic solar cells (OSCs). However, considering the advancements in materials and device performance, it is necessary to reexamine the photoelectric conversion in current-stage efficient OSCs. Here, we propose that the conjugated materials with specific three-dimensional donor-acceptor conjugated packing potentially exhibit distinctive charge photogeneration mechanism, which spontaneously split Wannier-Mott excitons to free carriers in pure phases. Subsequently, the pure planar p-n heterojunction (PHJ) OSCs based on green orthogonal solvents were prepared and exhibited comparable even greater performance to that of BHJ OSCs. More interestingly, by introducing PVDF-TrFE as intrinsic region to regulate built-in electric field of the device, the planar p-i-n PHJ OSCs achieved much higher efficiency (>18%) and stability. Moreover, a prominent efficiency of over 19% has been obtained via ternary optimization, which is the new efficiency record for PHJ OSCs up to date. This study points towards the distinguishing intrinsic free charge generation mechanism, opens up a new avenue for OSCs to collectively realize high-efficiency, long-term duration, and simplified device engineering for future commercialization.

An innovative BiOI@AgBiS2@NaYF4:Yb, Tm ternary heterostructure for efficient solar energy harvesting towards tetracycline hydrochloride degradation.

This study developed a BiOI@AgBiS2@NaYF4:Yb,Tm heterostructure photocatalyst. This design significantly enhances the generation and separation of charge carriers, leading to a marked improvement in solar energy harvesting. This advancement was effectively applied for the degradation of tetracycline hydrochloride. This strategy provides inspiration for designing and developing full-spectrum responsive photocatalysts.

Synergistic introduction of LSPR effect and Schottky junction: Cu@TiO2 charge regulation achieved efficient, stable photocatalytic removal

The local plasmon resonance effect (LSPR) and Schottky junction can effectively enhance the generation and separation efficiency of photo-generated carriers, but their synergistic effect has rarely been studied. In this...

Design of High Performance Graphene Thin Films Perovskite Solar Cells by Numerical Modeling Based on Coupled Differential Equations

In this study, graphene a two dimensional nanomaterial was prepared by modified Hummer’s method and the optical properties were explored using UV-visible spectroscopy to determine absorption coefficients at different wavelengths based on Beer-Lambert’s law. Graphene based lead-free methyl ammonium germanium halide solar cell was designed in the second stage using graphene oxide (GO) as carrier absorbers and transporters. Numerical modelling of the device in solar capacitance stimulating (SCAPS 1D) program based on second order differential equation was done. A photovoltaic parameters of 0.6227 V, 38.58 mAcm-2, 83.07 %, 19.95 % were recorded as the open-circuit voltage, current density, fill factor and power conversion efficiency (PCE) for FTO/GO/Perovskite/Cu2O/Au. Using the same settings for the second design, the Au/spiro-ometad/FASnI3/TiO2/FTO, the current density increases sharply from 0.50 V and with valence and conduction band at -0.35 eV and 1.78 eV respectively. The light transmittance and heat distribution across the device determine by origin pro-version 9.8.0200 indicated uniform transmission and absorption. The study showed that the presence of graphene, improved the optical transparency and enhanced carrier generation and interaction between other layers which optimized the electrical conductivity and efficiency of the solar cells when compared to previous studies in the literature. The results emphasized a viable approach in the design of efficient and stable solar cells at a reduced cost and optical losses. If mass produced can be deployed commercially due to enhanced solar energy absorption potential ahead of the Si based PVCs.

Impact of meta- and para-Direction External Side Chains in Y-Series Acceptors on the Molecular Packing and Charge Carrier Dynamics of Organic Photovoltaics.

The side-chain directions in nonfullerene acceptors (NFAs) strongly influence the intermolecular interactions in NFAs; however, the influence of these side chains on the morphologies and charge carrier dynamics of Y6-based acceptors remains underexplored. In this study, we synthesize four distinct Y6-based acceptors, i.e., meta-HOP-Y6-F (mF), meta-HOP-Y6-Cl (mCl), para-HOP-Y6-F (pF), and para-HOP-Y6-Cl (pCl), with outer side chains of alkoxy-2-ethylhexyl attached at the meta or para positions. Devices containing the meta-position acceptors blended with the polymer donor PM6 achieve power conversion efficiencies (PCEs) at least 1.27-fold higher than those of devices containing para-position acceptors. The enhanced performance can be attributed to the formation of donor-acceptor domains that are advantageous for charge carrier generation, transport, and collection. This is due to variations in phase aggregation that result from steric hindrance effects at the meta- and para-position acceptors. As a result, meta-position acceptors with lower steric hindrance improved π-π and lamellar stacking, whereas the para-position acceptors encountered excessive steric hindrance, reducing their photovoltaic efficiencies. Additionally, the meta-position acceptors demonstrate long charge carrier lifetimes, which suppress recombination in the charge transfer state and promote efficient charge separation. These results underline the critical role of side-chain direction in optimizing Y6-based acceptors for improving photovoltaic performance.

Dislocation‐Induced Local and Global Photoconductivity Enhancement and Mechanisms in Iron‐Doped SrTiO3

AbstractDislocations have a tremendous potential to alter band structure and transport properties. However, their impact on the optoelectronic properties of metal oxides is not thoroughly studied. This is mostly due to the early work on classical semiconductors, where dislocations are found to have detrimental effects. In this study, a simple method is developed to introduce a high density of dislocations over a large macroscopic volume of Fe‐doped SrTiO3 single crystals. As a result, the photoconductivity revealed by static and dynamic measurements increases by at least one order of magnitude. A detailed analysis based on photo‐Hall, spectral photoresponsivity, time‐resolved photocurrent, and conductive AFM, focusing on the quantum paraelectric state of SrTiO3, is presented to shed light on the possible mechanisms behind higher generated photocurrent. These findings indicate that the increased photoconductivity results from a higher charge carrier generation rate due to new energy states induced by dislocations, possibly accompanied by an enhancement of electron effective mass.