Up to 100% Formation Ratio of Doublet Exciton in Deep-Red Organic Light-Emitting Diodes Based on Neutral π-Radical

In a neutral π-radical-based organic light-emitting diode (OLED), although the emission comes from the doublet excitons and their transition to the ground state is spin-allowed, the upper limit of internal quantum efficiency (IQE) is not clear, 50% or 100%? In this work, the deep-red OLEDs based on a neutral π-radical were fabricated. Up to 100% doublet exciton formation ratio was obtained through rational designing device structure and host-guest doping system. This indicates the IQE of neutral π-radical-based OLEDs will reach 100% if the nonradiative pathways of radicals can be suppressed. The maximum external quantum efficiency of the optimized device is as high as 4.3%, which is among the highest values of deep-red/near-infrared OLEDs with nonphosphorescent materials as emitters. Our results also indicate that using partially reduced radical mixture as emitter may be a way to solve aggregation-caused quenching in radical-based OLEDs.

Highly Efficient LiYF4:Yb(3+), Er(3+) Upconversion Single Crystal under Solar Cell Spectrum Excitation and Photovoltaic Application

Luminescent upconversion is a promising way to harvest near-infrared (NIR) sunlight and transforms it into visible light that can be directly absorbed by active materials of solar cells and improve their power conversion efficiency (PCE). However, it is still a great challenge to effectively improve the PCE of solar cells with the assistance of upconversion. In this work, we demonstrate the application of the transparent LiYF4:Yb(3+), Er(3+) single crystal as an independent luminescent upconverter to improve the PCE of perovskite solar cells. The LiYF4:Yb(3+), Er(3+) single crystal is prepared by an improved Bridgman method, and its internal quantum efficiency approached to 5.72% under 6.2 W cm(-2) 980 nm excitation. The power-dependent upconversion luminescence indicated that under the excitation of simulated sunlight the (4)F(9/2)-(4)I(15/2) red emission originally results from the cooperation of a 1540 nm photon and a 980 nm photon. Furthermore, when the single crystal is placed in front of the perovskite solar cells, the PCE is enhanced by 7.9% under the irradiation of simulated sunlight by 7-8 solar constants. This work implies the upconverter not only can serve as proof of principle for improving PCE of solar cells but also is helpful to practical application.

Design Rules for High-Efficiency Quantum-Dot-Sensitized Solar Cells: A Multilayer Approach

The effect of multilayer sensitization in quantum-dot (QD)-sensitized solar cells is reported. A series of electrodes, consisting of multilayer CdSe QDs were assembled on a compact TiO2 layer. Photocurrent measurements along with internal quantum efficiency calculation reveal similar electron collection efficiency up to a 100 nm thickness of the QD layers. Moreover, the optical density and the internal quantum efficiency measurements reveal that the desired surface area of the TiO2 electrode should be increased only by a factor of 17 compared with a compact electrode. We show that the sensitization of low-surface-area TiO2 electrode with QD layers increases the performance of the solar cell, resulting in 3.86% efficiency. These results demonstrate a conceptual difference between the QD-sensitized solar cell and the dye-based system in which dye multilayer decreases the cell performance. The utilization of multilayer QDs opens new opportunities for a significant improvement of quantum-dot-sensitized solar cells via innovative cell design.

Inverted Quantum-Dot Light Emitting Diode Using Solution Processed p-Type WOx Doped PEDOT:PSS and Li Doped ZnO Charge Generation Layer

Quantum dots (QDs) are a promising material for emissive display with low-cost manufacturing and excellent color purity. In this study, we report colloidal quantum-dot light emitting diodes (QLEDs) with an inverted architecture with a solution processed charge generation layer (CGL) of p-type polymer (tungsten oxide doped poly(ethylenedioxythiophene)/polystyrenesulfonate,

PEDOT

PSS:WOx) and n-type metal oxide (lithium doped zinc oxide, LZO). The effective charge generation in solution processed p-n junction was confirmed by capacitance-voltage (C-V) and current density-electric field characteristics. It is also demonstrated that the performances of CGL based QLEDs are very similar when various substrates with different work functions are used.

On the Hole Injection for III-Nitride Based Deep Ultraviolet Light-Emitting Diodes

The hole injection is one of the bottlenecks that strongly hinder the quantum efficiency and the optical power for deep ultraviolet light-emitting diodes (DUV LEDs) with the emission wavelength smaller than 360 nm. The hole injection efficiency for DUV LEDs is co-affected by the p-type ohmic contact, the p-type hole injection layer, the p-type electron blocking layer and the multiple quantum wells. In this report, we review a large diversity of advances that are currently adopted to increase the hole injection efficiency for DUV LEDs. Moreover, by disclosing the underlying device physics, the design strategies that we can follow have also been suggested to improve the hole injection for DUV LEDs.

Intrinsic Optoelectronic Characteristics of MoS2 Phototransistors via a Fully Transparent van der Waals Heterostructure

In the past decade, intensive studies on monolayer MoS₂-based phototransistors have been carried out to achieve further enhanced optoelectronic characteristics. However, the intrinsic optoelectronic characteristics of monolayer MoS₂ have still not been explored until now because of unintended interferences, such as multiple reflections of incident light originating from commonly used opaque substrates. This leads to overestimated photoresponsive characteristics inevitably due to the enhanced photogating and photoconductive effects. Here, we reveal the intrinsic photoresponsive characteristics of monolayer MoS₂, including its internal responsivity and quantum efficiency, in fully transparent monolayer MoS₂ phototransistors employing a van der Waals heterostructure. Interestingly, as opposed to the previous reports, the internal photoresponsive characteristics do not significantly depend on the wavelength of the incident light as long as the electron-hole pairs are generated in the same k-space. This study provides a deeper understanding of the photoresponsive characteristics of MoS₂ and lays the foundation for two-dimensional materials-based transparent phototransistors.

A Direct Epitaxial Approach To Achieving Ultrasmall and Ultrabright InGaN Micro Light-Emitting Diodes (μLEDs)

A direct epitaxial approach to achieving ultrasmall and ultrabright InGaN micro light-emitting diodes (μLEDs) has been developed, leading to the demonstration of ultrasmall, ultraefficient, and ultracompact green μLEDs with a dimension of 3.6 μm and an interpitch of 2 μm. The approach does not involve any dry-etching processes which are exclusively used by any current μLED fabrication approaches. As a result, our approach has entirely eliminated any damage induced during the dry-etching processes. Our green μLED array chips exhibit a record external quantum efficiency (EQE) of 6% at ∼515 nm in the green spectral region, although our measurements have been performed on bare chips which do not have any coating, passivation, epoxy, or reflector, which are generally used for standard LED packaging in order to enhance extraction efficiency. A high luminance of >10⁷ cd/m² has been obtained on the μLED array bare chips. Temperature-dependent measurements show that our μLED array structure exhibits an internal quantum efficiency (IQE) of 28%. It is worth highlighting that our epitaxial approach is fully compatible with any existing microdisplay fabrication techniques.

Efficiency of True-Green Light Emitting Diodes: Non-Uniformity and Temperature Effects

External quantum efficiency of industrial-grade green InGaN light-emitting diodes (LEDs) has been measured in a wide range of operating currents at various temperatures from 13 K to 300 K. Unlike blue LEDs, the efficiency as a function of current is found to have a multi-peak character, which could not be fitted by a simple ABC-model. This observation correlated with splitting of LED emission spectra into two peaks at certain currents. The characterization data are interpreted in terms of non-uniformity of the LED active region, which is tentatively attributed to extended defects like V-pits. We suggest a new approach to evaluation of temperature-dependent light extraction and internal quantum efficiencies taking into account the active region non-uniformity. As a result, the temperature dependence of light extraction and internal quantum efficiencies have been evaluated in the temperature range mentioned above and compared with those of blue LEDs.

Improved Internal Quantum Efficiency and Light-Extraction Efficiency of Organic Light-Emitting Diodes via Synergistic Doping with Au and Ag Nanoparticles

This paper reports the distinct roles of Au and Ag nanoparticles (NPs) in organic light-emitting diodes (OLEDs) depending on their sizes. Au and Ag NPs that are 40 and 50 nm in size, respectively, are the most effective for enhancing the performance of green OLEDs. The external quantum efficiencies (EQEs) of green OLEDs doped with Au and Ag NPs (40 and 50 nm, respectively) are improved by 29.5% and 36.1%, respectively, while the power efficiencies (PEs) are enhanced by 47.9% and 37.5%, respectively. Furthermore, combining the Au and Ag NPs produces greater enhancements. The EQE and PE of the codoped OLEDs are improved by 63.9% and 68.8%, respectively, through the synergistic behavior of the different NPs. Finite-difference time-domain simulations confirm that the localized surface-plasmon resonance of the Au NPs near 580 nm improves the radiative recombination rate (k_rad) of green-light emitters locally (<50 nm), while the Ag NPs cause relatively long-range and broadband enhancements in k_rad. The simulations of various domain sizes verify that the light-extraction efficiency (LEE) can be enhanced by more than 4.2% by applying Ag NPs. Thus, size-controlled Au and Ag NPs can synergistically enhance OLEDs by improving both the internal quantum efficiency and LEE.

Spatially Resolved Doping Concentration and Nonradiative Lifetime Profiles in Single Si-Doped InP Nanowires Using Photoluminescence Mapping

We report an analysis method that combines microphotoluminescence mapping and lifetime mapping data of single semiconductor nanowires to extract the doping concentration, nonradiative lifetime, and internal quantum efficiency along the length of the nanowires. Using this method, the doping concentration of single Si-doped wurtzite InP nanowires are mapped out and confirmed by the electrical measurements of single nanowire devices. Our method has important implication for single nanowire detectors and LEDs and nanowire solar cells applications.

Nanoscale mapping of carrier collection in single nanowire solar cells using X-ray beam induced current

Here it is demonstrated how nanofocused X-ray beam induced current (XBIC) can be used to quantitatively map the spatially dependent carrier collection probability within nanostructured solar cells. The photocurrent generated by a 50 nm-diameter X-ray beam was measured as a function of position, bias and flux in single p-i-n doped solar-cell nanowires. The signal gathered mostly from the middle segment decays exponentially toward the p- and n-segments, with a characteristic decay length that varies between 50 nm and 750 nm depending on the flux and the applied bias. The amplitude of the XBIC shows saturation at reverse bias, which indicates that most carriers are collected. At forward bias, the relevant condition for solar cells, the carrier collection is only efficient in a small region. Comparison with finite element modeling suggests that this is due to unintentional p-doping in the middle segment. It is expected that nanofocused XBIC could be used to investigate carrier collection in a wide range of nanostructured solar cells.

Research Progress of AlGaN-Based Deep Ultraviolet Light-Emitting Diodes

AlGaN-based deep ultraviolet light-emitting diodes (DUV LEDs) have great application prospects in sterilization, UV phototherapy, biological monitoring and other aspects. Due to their advantages of energy conservation, environmental protection and easy miniaturization realization, they have garnered much interest and been widely researched. However, compared with InGaN-based blue LEDs, the efficiency of AlGaN-based DUV LEDs is still very low. This paper first introduces the research background of DUV LEDs. Then, various methods to improve the efficiency of DUV LED devices are summarized from three aspects: internal quantum efficiency (IQE), light extraction efficiency (LEE) and wall-plug efficiency (WPE). Finally, the future development of efficient AlGaN-based DUV LEDs is proposed.

Numerical Modeling of Silicon Photodiodes for High-Accuracy Applications Part I. Simulation Programs

The suitability of the semiconductor-device modeling program PC-1D for high-accuracy simulation of silicon photodiodes is discussed. A set of user interface programs optimized to support high-accuracy batch-mode operation of PC-1D for modeling the internal quantum efficiency of photodiodes is also described. The optimization includes correction for the dark current under reverse- and forward-bias conditions before calculating the quantum efficiency, and easy access to the highest numerical accuracy available from PC-1D, neither of which is conveniently available with PC-1D's standard user interface.

Optical Quality of InAs/InP Quantum Dots on Distributed Bragg Reflector Emitting at 3rd Telecom Window Grown by Molecular Beam Epitaxy

We present an experimental study on the optical quality of InAs/InP quantum dots (QDs). Investigated structures have application relevance due to emission in the 3rd telecommunication window. The nanostructures are grown by ripening-assisted molecular beam epitaxy. This leads to their unique properties, i.e., low spatial density and in-plane shape symmetry. These are advantageous for non-classical light generation for quantum technologies applications. As a measure of the internal quantum efficiency, the discrepancy between calculated and experimentally determined photon extraction efficiency is used. The investigated nanostructures exhibit close to ideal emission efficiency proving their high structural quality. The thermal stability of emission is investigated by means of microphotoluminescence. This allows to determine the maximal operation temperature of the device and reveal the main emission quenching channels. Emission quenching is predominantly caused by the transition of holes and electrons to higher QD's levels. Additionally, these carriers could further leave the confinement potential via the dense ladder of QD states. Single QD emission is observed up to temperatures of about 100 K, comparable to the best results obtained for epitaxial QDs in this spectral range. The fundamental limit for the emission rate is the excitation radiative lifetime, which spreads from below 0.5 to almost 1.9 ns (GHz operation) without any clear spectral dispersion. Furthermore, carrier dynamics is also determined using time-correlated single-photon counting.

Comparing Donor- and Acceptor-Originated Exciton Dynamics in Non-Fullerene Acceptor Blend Polymeric Systems

Non-fullerene type acceptors (NFA) have gained attention owing to their spectral extension that enables efficient solar energy capturing. For instance, the solely NFA-mediated absorbing region contributes to the photovoltaic power conversion efficiency (PCE) as high as ~30%, in the case of the solar cells comprised of fluorinated materials, PBDB-T-2F and ITIC-4F. This implies that NFAs must be able to serve as electron donors, even though they are conventionally assigned as electron acceptors. Therefore, the pathways of NFA-originated excitons need to be explored by the spectrally resolved photovoltaic characters. Additionally, excitation wavelength dependent transient absorption spectroscopy (TAS) was performed to trace the nature of the NFA-originated excitons and polymeric donor-originated excitons separately. Unique origin-dependent decay behaviors of the blend system were found by successive comparing of those solutions and pristine films which showed a dramatic change upon film formation. With the obtained experimental results, including TAS, a possible model describing origin-dependent decay pathways was suggested in the framework of reaction kinetics. Finally, numerical simulations based on the suggested model were performed to verify the feasibility, achieving reasonable correlation with experimental observables. The results should provide deeper insights in to renewable energy strategies by using novel material classes that are compatible with flexible electronics.

High-Performance Photodiodes Based on In-Situ Etched PbSe Colloidal Quantum Dots with Responses Extended to 2500 nm

The performance of PbSe colloidal quantum dot (CQD) based photodiodes with responses beyond 2000 nm was far from satisfactory and has rarely been reported. The difficulty in obtaining chemically stable large-sized PbSe CQDs was the main reason. In this work, chloride ions in weak acidic solvent were introduced to in-situ etch out the Se atoms on the surfaces of PbSe CQDs and formed a -Pb-Cl protection layer. As a result, there were no longer any easily oxidized Se atoms exposed to the ambient environment. The mechanism behind our method for stabilizing PbSe CQDs was distinct from the commonly reported ones such as attaching new adlayers directly. The photodiodes with the etched PbSe CQDs achieved 0.75 A/W responsivity at λ = 2200 nm, 0.15 V open circuit voltage and 100% internal quantum efficiency without the assist of photoconductive gains, which were the best records for PbSe-based photodiodes working beyond 2000 nm.

Drastic Effect of Sequential Deposition Resulting from Flux Directionality on the Luminescence Efficiency of Nanowire Shells

Core-shell nanowire heterostructures form the basis for many innovative devices. When compound nanowire shells are grown by directional deposition techniques, the azimuthal position of the sources for the different constituents in the growth reactor, substrate rotation, and nanowire self-shadowing inevitably lead to sequential deposition. Here, we uncover for In_0.15Ga_0.85As/GaAs shell quantum wells grown by molecular beam epitaxy a drastic impact of this sequentiality on the luminescence efficiency. The photoluminescence intensity of shell quantum wells grown with a flux sequence corresponding to migration enhanced epitaxy, that is, when As and the group-III metals essentially do not impinge at the same time, is more than 2 orders of magnitude higher than for shell quantum wells prepared with substantially overlapping fluxes. Transmission electron microscopy does not reveal any extended defects explaining this difference. Our analysis of photoluminescence transients shows that co-deposition has two detrimental microscopic effects. First, a higher density of electrically active point defects leads to internal electric fields reducing the electron-hole wave function overlap. Second, more point defects form that act as nonradiative recombination centers. Our study demonstrates that the source arrangement of the growth reactor, which is of mere technical relevance for planar structures, can have drastic consequences for the material properties of nanowire shells. We expect that this finding holds good also for other alloy nanowire shells.

Resonant inelastic tunneling using multiple metallic quantum wells

Tunnel nanojunctions based on inelastic electron tunneling (IET) have been heralded as a breakthrough for ultra-fast integrated light sources. However, the majority of electrons tend to tunnel through a junction elastically, resulting in weak photon-emission power and limited efficiency, which have hindered their practical applications to date. Resonant tunneling has been proposed as a way to alleviate this limitation, but photon-emissions under resonant tunneling conditions have remained unsatisfactory for practical IET-based light sources due to the inherent contradiction between high photon-emission efficiency and power. In this work, we introduce a novel approach that leverages much stronger resonant tunneling enhancement achieved by multiple metallic quantum wells, which has enabled the internal quantum efficiency to reach ∼1 and photon-emission power to reach ∼0.8 µW/µm2. Furthermore, this method is applicable with different electronic lifetimes ranging from 10 fs to 100 fs simultaneously, bringing practical implementation of IET-based sources one step closer to reality.

External Control of GaN Band Bending Using Phosphonate Self-Assembled Monolayers

We report on the optoelectronic properties of GaN(0001) and (11̅00) surfaces after their functionalization with phosphonic acid derivatives. To analyze the possible correlation between the acid's electronegativity and the GaN surface band bending, two types of phosphonic acids, n-octylphosphonic acid (OPA) and 1H,1H,2H,2H-perfluorooctanephosphonic acid (PFOPA), are grafted on oxidized GaN(0001) and GaN(11̅00) layers as well as on GaN nanowires. The resulting hybrid inorganic/organic heterostructures are investigated by X-ray photoemission and photoluminescence spectroscopy. The GaN work function is changed significantly by the grafting of phosphonic acids, evidencing the formation of dense self-assembled monolayers. Regardless of the GaN surface orientation, both types of phosphonic acids significantly impact the GaN surface band bending. A dependence on the acids' electronegativity is, however, only observed for the oxidized GaN(11̅00) surface, indicating a relatively low density of surface states and a favorable band alignment between the surface oxide and acids' electronic states. Regarding the optical properties, the covalent bonding of PFOPA and OPA on oxidized GaN layers and nanowires significantly affects their internal quantum efficiency, especially in the nanowire case due to the large surface-to-volume ratio. The variation in the internal quantum efficiency is related to the modification of both the internal electric fields and surface states. These results demonstrate the potential of phosphonate chemistry for the surface functionalization of GaN, which could be exploited for selective sensing applications.

Surface Passivation of III-V GaAs Nanopillars by Low-Frequency Plasma Deposition of Silicon Nitride for Active Nanophotonic Devices

Numerous efforts have been devoted to improve the electronic and optical properties of III-V compound materials via reduction of their nonradiative states, aiming at highly efficient III-V sub-micrometer active devices and circuits. Despite many advances, the poor reproducibility and short-term passivation effect of chemical treatments, such as sulfidation and nitridation, requires the use of protective encapsulation methods, not only to protect the surface, but also to provide electrical isolation for device manufacturing. There is still a controversial debate on which combination of chemical treatment and capping dielectric layer can best reproducibly protect the crystal surface of III-V materials while being compatible with readily available semiconductor-foundry plasma deposition methods. This work reports on a systematic experimental study on the role of sulfide ammonium chemical treatment followed by dielectric coating (either silicon oxide or nitride) in the passivation effect of GaAs/AlGaAs nanopillars. Our results conclusively show that, under ambient conditions, the best surface passivation is achieved using ammonium sulfide followed by encapsulation with a thin layer of silicon nitride by low-frequency plasma-enhanced chemical deposition. Here, the sulfurized GaAs surfaces, high level of hydrogen ions, and low-frequency (380 kHz) excitation plasma that enable intense bombardment of hydrogen, all seem to provide a combined active role in the passivation mechanism of the pillars by reducing the surface states. As a result, we observe up to a 29-fold increase of the photoluminescence (PL) integrated intensity for the best samples as compared to untreated nanopillars. X-ray photoelectron spectroscopy analysis confirms the best treatments show remarkable removal of gallium and arsenic native oxides. Time-resolved micro-PL measurements display nanosecond lifetimes resulting in a record-low surface recombination velocity of ∼1.1 × 10⁴ cm s^-1 for dry-etched GaAs nanopillars. We achieve robust, stable, and long-term passivated nanopillar surfaces, which creates expectations for remarkable high internal quantum efficiency (IQE > 0.5) in nanoscale light-emitting diodes. The enhanced performance paves the way to many other nanostructures and devices such as miniature resonators, lasers, photodetectors, and solar cells, opening remarkable prospects for GaAs active nanophotonic devices.

Dilute Donor Organic Solar Cells Based on Non-fullerene Acceptors

The advent of small molecule non-fullerene acceptor (NFA) materials for organic photovoltaic (OPV) devices has led to a series of breakthroughs in performance and device lifetime. The most efficient OPV devices have a combination of electron donor and acceptor materials that constitute the light absorbing layer in a bulk heterojunction (BHJ) structure. For many BHJ-based devices reported to date, the weight ratio of donor to acceptor is near equal. However, the morphology of such films can be difficult to reproduce and manufacture at scale. There would be an advantage in developing a light harvesting layer for efficient OPV devices that contains only a small amount of either the donor or acceptor. In this work we explore low donor content OPV devices composed of the polymeric donor PM6 blended with high performance NFA materials, Y6 or ITIC-4F. We found that even when the donor:acceptor weight ratio was only 1:10, the OPV devices still have good photoconversion efficiencies of around 6% and 5% for Y6 and ITIC-4F, respectively. It was found that neither charge mobility nor recombination rates had a strong effect on the efficiency of the devices. Rather, the overall efficiency was strongly related to the film absorption coefficient and maintaining adequate interfacial surface area between donor and acceptor molecules/phases for efficient exciton dissociation.

Efficiency of MAPbI3-Based Planar Solar Cell Analyzed by Its Thickness-Dependent Exciton Formation, Morphology, and Crystallinity

In spite of the impressive progresses regarding perovskite-type solar cells, a clear understanding about underlying mechanisms therein is still sparse, especially because of the absence of spatially resolved device characteristics which should be linked to exciton formation efficiency, morphology, and crystallinity being estimated as functions of positions within active layers. Here, the planar CH₃NH₃PbI₃ (MAPbI₃) perovskite solar cells (PeSCs) with ZnO as the electron-transporting layer (ETL) were fabricated. By varying the wide range of MAPbI₃ active-layer thickness, we estimate their device parameters and external quantum efficiencies in addition to internal absorption spectra (Q) by means of the transfer matrix method. Furthermore, the spectrally and spatially resolved internal quantum efficiencies (IQEs) as a function of the active-layer thickness within PeSCs were calculated, and the relationship between IQE and device parameters extracted from the current-voltage ( J- V) behaviors was discussed. It was found that the PeSC with MAPbI₃ film thickness around 303 nm has a relatively high IQE and PCE, indicating that there is more power loss of PeSCs when the thickness of the MAPbI₃ layer is either less or more than about 300 nm. Furthermore, time-resolved photoluminescence together with the thickness-dependent morphology and crystallinity of the MAPbI₃ film demonstrate that there are two power loss processes in the fabricated PeSCs: one at the ZnO/MAPbI₃ interface and the other in bulk. The present research is beneficial for further understanding of the fundamental physics for the PeSCs based on the ZnO ETL.

Spatial Balance of Photogenerated Charge Carriers in Active Layers of Polymer Solar Cells

Bulk heterojunction polymer solar cells (PSCs) blended with non-fullerene-type acceptors (NFAs) possess good solar power conversion efficiency and compatibility with flexible electronics, rendering them good candidates for mobile photovoltaic applications. However, their internal absorption performance and mechanism are yet to be fully elucidated because of their complicated interference effect caused by their multilayer device structure. The transfer matrix method (TMM) is ideal for analyzing complex optical electric fields by considering multilayer interference effects. In this study, an active layer (AL) thickness-dependent TMM is used to obtain accurate information on the photon-capturing mechanisms of NFA-based PSCs for comparison with experimental results. Devices with AL thicknesses of 40-350 nm were prepared, and the AL-thickness-dependent device parameters with incident photon-to-current efficiency spectra were compared with the calculated internal absorption spectra of the TMM. The spectrally and spatially resolved spectra as a function of the AL thickness and excitation wavelength revealed that the power conversion efficiency of the NFA-blended PSC decreased with the increasing AL thickness after reaching a maximum of ~100 nm; by contrast, the internal absorption efficiency showed the opposite trend. Furthermore, the TMM spectra indicated that the spatial distribution of the photogenerated charge carriers became significantly imbalanced as the AL thickness increased, implying that the AL-dependent loss stemmed from the discrepancy between the absorption and the extracted charge carriers.

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.