Efficient Hole Transfer Research Articles

Enhanced photoelectric desalination of Co3O4@NC/BiVO4 photoanode via in-situ construction of hole transport layer

The solar-driven photoelectrochemical desalination (SD-PED) technology, as a new emerging desalination technique, has been developed and attracted the increasing attention. However, practical application remains hampered by several constraints, including the rapid deterioration of photocurrent, and the long-term stability of system. In this research, MOF-derived nitrogen-doped carbon@Co3O4/BVO (Co3O4@NC/BVO) heterostructured photoanode was design for efficient and durable solar driven redox desalination. It exhibits an initial photocurrent of 2.40 mA/cm2 and a desalination rate of 69.01 μg/(cm2·min) in the zero-bias state using the light as the driving force, without consuming electrical energy. Furthermore, the solar energy consumption of the photoanode is 0.187 μmol/J. The salt removal rate fluctuates within 1.36 μg/(cm2·min) throughout five cycles without any substantial decrease. Photo-luminescence, EIS and Mott-Schottky analysis are also performed to investigate interface reaction, charge separation and transfer mechanism between photoanode and electrolyte. The analysis of the charge-transfer paths on the heterojunction interface is conducted through in situ irradiation XPS. Further analysis of the generation and separation of •OH and h+ in the Co3O4@NC/BVO photoanode using electron paramagnetic resonance (EPR) showed that Co3O4@NC as an efficient hole transfer layer can effectively promote the separation and transfer of photo-generated electrons and holes. The excellent desalination performance is attributed to the synergistic effect of electron transfer in the Co3O4@NC/BVO heterojunction and hole transport in the Co3O4@NC efficient hole transport layer. This work is significant for the development of solar redox flow desalination.

Regulating Electron‐Phonon Coupling by Solid Additive for Efficient Organic Solar Cells

AbstractStrong electron‐phonon coupling can hinder exciton transport and induce undesirable non‐radiative recombination, resulting in a shortened exciton diffusion distance and constrained exciton dissociation in organic solar cells (OSCs). Therefore, suppressing electron‐phonon coupling is crucially important for achieveing high‐performance OSCs. Here, we employ the solid additive to regulating electron‐phonon coupling in OSCs. The planar configuration of SA1 confers a significant advantage in suppressing lattice vibrations in the active layers, reducing the scattering of excitons by phonons. Consequently, a slow but sustained hole transfer process is identified in the SA1‐assisted film, indicating an enhancement in hole transfer efficiency. Prolonged exciton diffusion length and exciton lifetime are achieved in the blend film processed with SA1, attributed to a low non‐radiative recombination rate and low energetic disorder for charge carrier transport. As a result, a high efficiency of 20 % was achieved for ternary device with a remarkable short‐circuit current. This work highlights the important role of suppressing electron‐phonon coupling in improving the photovoltaic performance of OSCs.

Polyaniline as a solid-state charge conductor for enhanced photocatalytic hydrogen production and value-added disulfide synthesis

Efficient transfer and maximal utilization of photogenerated electrons and holes in photocatalytic processes, along with the simultaneous production of hydrogen and high-value chemicals, represent a promising approach for effective solar energy utilization. Herein, polyaniline (PANI) was employed as a charge conductor to enhance the heterojunction structure between g-C3N4 and CdS, thereby facilitating the efficient interfacial transfer of photogenerated carriers. The obtained composite has demonstrated outstanding photocatalytic performance in both water splitting for hydrogen production and the dehydrogenation coupling of thiols. The hydrogen evolution efficiency of g-C3N4-PANI-CdS composite in water splitting is 41.67 times higher than that of the original g-C3N4. Additionally, the sample exhibits efficient splitting and re-polymerization capabilities for 4-methoxythiophenol (4-MTP), achieving the efficient hydrogen production and bis (4-methoxyphenyl) disulfide (4-MPD) synthesis concurrently. Comprehensive characterization methods confirm that PANI acts as a highly conductive layer, accelerating rapid charge transfer and separation at the interface between g-C3N4 and CdS, significantly improving the utilization of surface active sites. This study provides valuable insights for the future advancements in photocatalytic hydrogen generation and disulfides synthesis.

Ultrafast Charge Transfer Cascade in a Mixed-Dimensionality Nanoscale Trilayer

Innovation in optoelectronic semiconductor devices is driven by a fundamental understanding of how to move charges and/or excitons (electron-hole pairs) in specified directions for doing useful work, e.g. for making fuels or electricity. The diverse and tunable electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) and one-dimensional (1D) semiconducting single-walled carbon nanotubes (s-SWCNTs) make them good quantum confined model systems for fundamental studies on charge and exciton transfer across heterointerfaces. In nature, the photosynthetic apparatus achieves long-lived charge separation through a charge transfer cascade that consists of a series of thermodynamically downhill charge transfer reactions. Inspired by photosynthesis we create a unique mixed-dimensionality 2D/1D/2D MoS2/SWCNT/WSe2 hetero-trilayer. Photoexcitation of this trilayer heterostructure allows us to overcome both intralayer and interlayer exciton binding energies, resulting in coulombically unbound charges with microsecond recombination lifetimes. In contrast to previously demonstrated 2D/2D/2D trilayers based solely on monolayer TMDC layers, the very large charge mobilities and extended electron network of the 1D semiconducting SWCNT layer helps charges delocalize and diffuse away from the interface at which each type of charge is generated. Interestingly, the hetero-trilayer also appears to enable efficient hole transfer from SWCNTs to WSe2, which is not observed in the identically prepared WSe2/SWCNT heterobilayer, suggesting that new dynamic pathways may be opened by increasing the complexity of nanoscale heterostructures. Our work suggests "mixed-dimensionality" TMDC/SWCNT based hetero-trilayers as both interesting model systems for mechanistic studies of carrier dynamics at nanoscale heterointerfaces, and for potential applications in advanced optoelectronic systems.

Constructing cascade electric fields and sulfur vacancies in Ni3S4/NiS2/v-Zn3In2S6 photocatalyst for efficient degradation of contaminants and H2 production

The increasing environmental pollution and looming energy crisis necessitate the development of advanced photocatalysts that demonstrate efficient separation and transfer of the photo-generated holes and electrons, as well as multiple functions to address the above issues. Herein, a bifunctional Ni3S4/NiS2/v-Zn3In2S6 photocatalyst has been constructed to degrade environmental hormones and antibiotics with simultaneous H2 production. Sulfur vacancies have been engineered in the Zn3In2S6 from a kinetic point of view to accelerate the separation of photogenerated charge carriers and act as active sites. Ni3S4 and NiS2 are introduced to construct cascade electric fields with Zn3In2S6 via ohmic junctions for spatially separated charge carriers and reduced hydrogen evolution potential. As a result, the composite exhibits enhanced photocatalytic H2 production and efficient degradation of bisphenol A, norfloxacin, and tetracycline, respectively. Specifically, the degradation pathways of BPA have been investigated based on Fukui calculations and liquid chromatography-mass spectrometry techniques. This work may shed new light on the design and construction of dual-function photocatalysts for wastewater treatment and H2 production.

Infrared Photodetector Based on van der Waals MoS2/MoTe2 Hetero‐Bilayer Modulated by Photogating

AbstractPhotodetectors based on 2D hetero‐bilayers can overcome the bandgap limitations of individual 2D monolayers and operate at relatively long wavelengths. However, ultra‐low light absorptions within hetero‐bilayers result in extremely weak photoresponsivity. Here, an infrared photodetector based on the MoS2/MoTe2 type‐II hetero‐bilayer is demonstrated to reach a photoresponsivity of 0.55 A W−1 at 1550 nm, well beyond energy band cut‐offs of monolayer MoS2 and MoTe2, primarily resulted from the photogating effect. Raman and photoluminescence (PL) spectroscopy reveal strong interlayer couplings in the hetero‐bilayer, and a broad PL peak around 1550 nm is observed that is ascribed to interlayer transitions of carriers. The photodetector showcases a broadband detection capability from 1100 to 1700 nm, with a peak at 1550 nm corresponding to the interlayer absorption. Electrical characterization of the hetero‐bilayer‐based field‐effect transistor and kelvin probe force microscopy reveal efficient interlayer hole transfer. The highly responsive MoS2/MoTe2 infrared photodetector offers a large photo‐gain of ≈103 and a time constant of 130 ms. The research illuminates how interlayer transitions affect 2D hetero‐bilayer‐based photodetectors and advances the utilization of layered semiconductor heterostructures.

The optoelectronic properties of acetylene based compounds as hole transporter in perovskite solar cells: A computational study

Hole transport materials (HTMs)are pivotal components inperovskite solar cells (PSCs), significantly influencing theirpower conversion efficiency (PCE). This study explores the potential of variousdiacetylide-triphenylamine (DATPA) derivatives (HTMs 1–8)to function as hole transporters, employingdensity functional theory (DFT)andtime-dependent density functional theory (TD-DFT)calculations.The energy levels of thehighest occupied molecular orbital (HOMO)andlowest unoccupied molecular orbital (LUMO), as well as theband gap, were computed using theB3LYP/6-311G(d)level of theory. The findings reveal that, with the exception of HTM 8, these compounds exhibit suitable HOMO and LUMO levels relative to the perovskite layer and possess a lower band gap energy compared to the commonly usedspiro-OMeTAD.Additionally, the calculation ofhole mobility (Kh)using the Marcus method demonstrated a satisfactory value, substantiating the applicability of these compounds as HTMs. Further calculations of parameters such ashole reorganization energy (λh),absolute hardness (η),ionization potential (IP),electronic affinity (EA),solubility (ΔGsolv), andexciton binding energy (Eb)affirm that these compounds are promising candidates for hole transport in perovskite solar cells. Notably, the compoundHTM 2 (NMe2-DATPA)outperforms the others in hole transfer efficiency.

Delocalizing Excitation for Highly-Active Organic Photovoltaic Catalysts.

Localized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo-induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron-phonon coupling via rational fluoro-substitution. The optimized 2FBP-4F catalyst we develop here exhibits a minimized Huang-Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP-4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP-4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6-561.8 mmol h-1 g-1) for hydrogen evolution than the control PM6 : BP-4F and PM6 : 2FBP-6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm-2).

Delocalizing Excitation for Highly‐Active Organic Photovoltaic Catalysts

AbstractLocalized excitation in traditional organic photocatalysts typically prevents the generation and extraction of photo‐induced free charge carriers, limiting their activity enhancement under illumination. Here, we enhance delocalized photoexcitation of small molecular photovoltaic catalysts by weakening their electron‐phonon coupling via rational fluoro‐substitution. The optimized 2FBP‐4F catalyst we develop here exhibits a minimized Huang–Rhys factor of 0.35 in solution, high dielectric constant and strong crystallization in the solid state. As a result, the energy barrier for exciton dissociation is decreased, and more importantly, polarons are unusually observed in 2FBP‐4F nanoparticles (NPs). With the increased hole transfer efficiency and prolonged charge carrier lifetime highly related to enhanced exciton delocalization, the PM6 : 2FBP‐4F heterojunction NPs at varied concentration exhibit much higher optimized photocatalytic activity (207.6–561.8 mmol h−1 g−1) for hydrogen evolution than the control PM6 : BP‐4F and PM6 : 2FBP‐6F NPs, as well as other reported photocatalysts under simulated solar light (AM 1.5G, 100 mW cm−2).

Efficient Electron Transfer Driven by Excited-State Structural Relaxation in Corrole-Perylenedimiide Dyad.

A sterically encumbered trans-A2B-corrole possessing a perylenediimide (PDI) scaffold in close proximity to the macrocycle has been synthesized via a straightforward route. Electronic communication as probed via steady-state absorption or cyclic voltammetry is weak in the ground state, in spite of the corrole ring and PDI being bridged by an o-phenylene unit. The TDDFT excited-state geometry optimization suggests after excitation the interchromophoric distance is markedly reduced, thus enhancing the through-space electronic coupling between the corrole and the PDI. This is corroborated by the strong deviation of the emission spectrum originating from both PDI and corrole in the dyad. Selective excitation of both donor and acceptor units triggers efficient sub-picosecond electron transfer and hole transfer, respectively, followed by fast charge recombination. In comparison to previously studied corrole-PDI dyads, both charge separation and charge recombination occur faster, because of the structural relaxation in the excited state.

SiQDs-mediated highly efficient hole transfer for photocatalytic overall water splitting over Cu-doped ZnIn2S4

Sluggish hole transfer and the resulting pronounced charge recombination hinder the efficiency of photocatalytic overall water splitting. Herein, we present Si quantum dots (SiQDs) as hole transporter to construct SiQDs/Cu-doped ZnIn2S4 heterojunction photocatalysts (Cu0.48SZ) for overall water splitting. Under visible light illumination, Cu0.48SZ exhibits highly stable overall water-splitting activity of 210 μmol g−1 h−1 H2 and 97 μmol g−1 h−1 O2 with an apparent quantum yield (AQY) of 2.57 % at 420 nm. Results demonstrate that the synergy of SiQDs and Cu doping enhances carrier-separation efficiency and reduce surface kinetic barriers, leading to high photocatalytic performance. The presence of SiQDs effectively accelerates the transfer of photoexcited holes and avoids the self-oxidation of ZnIn2S4, favoring water oxidation. The Cu doping increases the electron density around the S atoms of ZnIn2S4 and thus promotes water reduction. This work extends the application of SiQDS as efficient hole transporter for photocatalytic overall water splitting.

Investigation of the charge injection from Organometal halide perovskite to a hole transport layer using a heterodyne transient grating spectroscopic technique

The responses of MAPbI3 coated by ZnO with and without CuSCN were observed using near-field heterodyne transient grating spectroscopic technique for the investigation of the effect of the insertion of CuSCN, the hole transport layer, on the hole transfer efficiency in the perovskite-based solar cell. We revealed that the recombination arising from the surface trapped electrons in ZnO, the electron transport layer, was retarded when CuSCN was inserted in the film, which could be attributed to the spatially separated charge carriers more sufficiently, caused by the increase in the distance between the electron transport layer and the conducting substrate.

Collaborative role of co-doping and surface modifying for adjusting surface state of hematite to release the photoelectrochemical activity

Inhibition of bulk and interfacial charge carrier recombination is an urgent solution to release furthest the photoelectrochemical potential abilities of hematite photoelectrode. Herein, the Zr-Y dual metal co-doping engineering and Co/Fe dual metal-organic frameworks cocatalyst layer were employed for modifying hematite photoanode. The novel CoFe-MOF/Zr-Y:Fe2O3 nanoarray composite photoanode exhibits higher PEC activity, the photocurrent density at 1.23 V vs.RHE is increased by 4.7 times than that of the pristine α-Fe2O3. The gain in bulk charge separation efficiency was mainly attributed to the synergistic effect between the two doping ions to improve the electrical conductivity. Wherein, Zr4+ doping endows more free electrons in the bulk α-Fe2O3 and Y3+ introduction causes polaron mobility enhancement. For another, co-doping could reduce the recombination surface state, but form the intermediate surface state to promote hole transfer, thus effectively inhibiting the severe recombination of photogenerated electrons and holes. Furthermore, the CoFe-MOF cocatalyst coating with abundant active sites not only expedites the oxygen evolution reaction kinetics process, but also passivates the surface hole trapping state more thoroughly, resulting in efficient interfacial hole transfer and utilization. This work affords a new collaborative role of co-doping and surface modifying effective avenue for adjusting surface state of hematite to release the photoelectrochemical activity.

Ultrafast Charge Transfer Cascade in a Mixed-Dimensionality Nanoscale Trilayer.

Innovation in optoelectronic semiconductor devices is driven by a fundamental understanding of how to move charges and/or excitons (electron-hole pairs) in specified directions for doing useful work, e.g., for making fuels or electricity. The diverse and tunable electronic and optical properties of two-dimensional (2D) transition metal dichalcogenides (TMDCs) and one-dimensional (1D) semiconducting single-walled carbon nanotubes (s-SWCNTs) make them good quantum confined model systems for fundamental studies of charge and exciton transfer across heterointerfaces. Here we demonstrate a mixed-dimensionality 2D/1D/2D MoS2/SWCNT/WSe2 heterotrilayer that enables ultrafast photoinduced exciton dissociation, followed by charge diffusion and slow recombination. Importantly, the heterotrilayer serves to double charge carrier yield relative to a MoS2/SWCNT heterobilayer and also demonstrates the ability of the separated charges to overcome interlayer exciton binding energies to diffuse from one TMDC/SWCNT interface to the other 2D/1D interface, resulting in Coulombically unbound charges. Interestingly, the heterotrilayer also appears to enable efficient hole transfer from SWCNTs to WSe2, which is not observed in the identically prepared WSe2/SWCNT heterobilayer, suggesting that increasing the complexity of nanoscale trilayers may modify dynamic pathways. Our work suggests "mixed-dimensionality" TMDC/SWCNT based heterotrilayers as both interesting model systems for mechanistic studies of carrier dynamics at nanoscale heterointerfaces and for potential applications in advanced optoelectronic systems.

Polyol-assisted efficient hole transfer and utilization at the Si-based photoanode/electrolyte interface

The sluggish kinetics of the anodic oxygen evolution reaction significantly restricts the efficiency of silicon (Si)-based photoelectrochemical (PEC) cells. In this study, we employ microfabrication technology to batch-prepare reproducible Si substrates, and develop a facile electrodeposition technique to load high-quality nickel film onto the substrates. Innovatively, we introduce energetically favorable polyols (such as glycerol, propylene glycol, and ethylene glycol) into the electrolyte, resulting in a remarkably low onset potential and a high hole injection efficiency during the PEC oxidation process. Taking glycerol as an example, in-situ impendence spectra provide real-time evidence for the accelerated hole transfer and utilization at the photoanode/electrolyte interface in the presence of glycerol. Mechanistic studies further reveal that glycerol undergoes synergistic oxidation mediated by holes and catalysts. Finally, by intergrating a solar thermoelectric generator into a PEC polyol oxidation cell, the self-powered system demonstrates promising potential for producing valuable products solely by harnessing solar energy.

Achieving Long-Lived Charge Separated State through Ultrafast Interfacial Hole Transfer in Redox Sites-Isolated CdS Nanorods for Enhanced Photocatalysis.

As opposed to natural photosynthesis, a significant challenge in a semiconductor-based photocatalyst is the limited hole extraction efficiency, which adversely affects solar-to-fuel efficiency. Recent studies have demonstrated that photocatalysts featuring spatially isolated dual catalytic oxidation/reduction sites can yield enhanced hole extraction efficiencies. However, the decay dynamics of excited states in such photocatalysts have not been explored. Here a ternary barbell-shaped CdS/MoS2/Cu2S heterostructure is prepared, comprising CdS nanorods (NRs) interfaced with MoS2 nanosheets at both ends and Cu2S nanoparticles on the sidewall. By using transient absorption (TA) spectra, highly efficient charge separation within the CdS/MoS2/Cu2S heterostructure are identified. This is achieved through directed electron transfer to the MoS2 tips at a rate constant of >8.3 × 109 s-1 and rapid hole transfer to the Cu2S nanoparticles on the sidewall at a rate of >6.1 × 1010 s-1, leading to an exceptional overall charge transfer constant of 2.3 × 1011 s-1 in CdS/MoS2/Cu2S. The enhanced hole transfer efficiency results in a remarkably prolonged charge-separated state, facilitating efficient electron accumulation within the MoS2 tips. Consequently, the ternary CdS/MoS2/Cu2S heterostructure demonstrates a 22-fold enhancement in visible-light-driven H2 generation compare to pure CdS nanorods. This work highlights the significance of efficient hole extraction in enhancing the solar-to-H2 performance of semiconductor-based heterostructure.

Exceptional PbS/CsPbCl3 heterostructure based on the structural, electronic and optical properties of PbS/CsPbX3(X=Cl, Br, I)

The construction of heterojunction between NIR photoelectric materials and other types of materials has the potential to improve the performance of VIS-NIR photoelectric materials and broaden the absorption spectrum. In this study, the properties and theoretical calculations are carried out using the near-infrared photoelectric material PbS and the perovskite material CsPbX3 (X = Cl, Br, I) to build heterostructures. The appropriate lattice mismatch rates (4.5 %, 2 % and 4.6 %) between PbS and CsPbX3 (X = Cl, Br, I) ensure the feasibility of constructing PbS/CsPbX3 (X = Cl, Br, I) heterogeneous structures. The electronic properties calculations revealed physical mechanisms that improve luminous efficiency. Notably, the I-type band alignment (-5.02eV < PbS < −3.77eV, −5.85eV < CsPbX3 (X = Cl, Br, I) < -3.35eV) at the PbS/CsPbX3 (X = Cl, Br, I) interface facilitates efficient electron and hole transfer from the CsPbX3 (X = Cl, Br, I) quantum dots to the PbS material, which was further validated by the observed difference in charge density. Among them, the electron cloud of PbS/CsPbCl3 heterostructure is more obvious, and the charge transfer ability is better than that of the other two heterostructures. The heterostructures extend the light absorption range of CsPbX3 (X = Cl, Br, I) from visible to near-infrared under the influence of PbS. By comparing the light absorption functions, it is found that PbS/CsPbI3> PbS/CsPbCl3> PbS/CsPbBr3 in this range. Regarding comprehensive stability, charge density transfer, and optical properties, PbS/CsPbCl3 has the best performance. Under the premise of ensuring stability, different light absorption characteristics can be achieved by adjusting the composition of halogen atoms in PbS/CsPbCl3. This study provides a theoretical basis for enhancing the performance of the PbS/CsPbX3 (X = Cl, Br, I) heterostructures in VIS-NIR optoelectronic materials through investigations of their electronic and optical properties. It yields a promising approach for the design of high-performance VIS-NIR heterogeneous materials.

Perovskite Solar Cells With Modified Carbon Electrode and CuSCN Interlayer Processed Under Ambient Conditions

Carbon‐based perovskite solar cells (PSCs) have the advantages of a long lifetime and are compatible with highly scalable manufacturing processes. The use of carbon electrodes and the absence of a hole selective layer (HSL) promote a simplified fabrication process. However, the efficiency of HSL‐free carbon‐based PSCs is inferior to PSCs that utilize metal electrodes and HSL due to poor hole extraction at the perovskite/carbon interface. To overcome those issues, researchers added an interlayer on the perovskite/carbon interface or incorporated additive material into the carbon layer. However, there is limited research on utilizing both strategies to improve carbon‐based PSC performance. Here, we use CuSCN as an interlayer between the perovskite/carbon interface and a carbon additive in carbon‐based PSCs. By utilizing both strategies, the charge transfer of carbon‐based PSC was significantly improved compared to carbon‐based PSC utilizing only one improvement strategy. Confirmed by photoluminescence (PL) and electrochemical impedance spectroscopy (EIS) characterizations, the CuSCN interlayer and CuSCN‐incorporated carbon electrode enable more efficient hole transfer, resulting in an increased power conversion efficiency from 0.58% to 5.06%. The proposed PSC structure shows promising results for further improving carbon‐based PSC performance.

Suppressed non-radiative loss and efficient hole transfer at a small highest occupied molecular orbital offset endows binary organic solar cells with 19.73% efficiency and a small efficiency-cost gap

Two novel acceptors are designed and synthesized, and the PTQ11:PEH-F binary system is highly promising for industrial cost-effective organic photovoltaics.

Enhanced desulfurization performance of model fuel by Cu-ZnO/TiO2 heterostructure.

A facile hydrothermal approach was employed to synthesize a novel Cu-ZnO/TiO2 Z-heterojunction with a high density of defects, which was then utilized for the oxidative desulfurization process, demonstrating excellent photodegradation performance. The results showed that by adjusting components such as Cu, ZnO, and TiO2, the removal efficiency of DBT reached 88.12% within a duration of 240 min. In the 5 repeated experiments, 7.5%Cu-ZnO/TiO2 still exhibited high stability and could be reused. The improved photocatalytic performance of the 7.5%Cu-ZnO/TiO2 composite can be attributed to its high light absorption capability and well-matched energy levels, which are due to the abundant presence of imperfections. The adoption of a Z-heterojunction has enabled efficient separation and transfer of photo-generated electrons and holes (e-/h+), thereby reducing the probability of charge carrier recombination.