Carrier Lifetime Research Articles

Unlocking low-concentration NH3 gas sensing: An innovative MOF-derived In2O3/Co3O4 nanocomposite approach

Ammonia (NH3) is an odorless gas with a pungent smell that can affect health differently based on exposure and concentration. In this study, indium oxide was decorated with cobalt oxide (In2O3/Co3O4) flower-like nanocomposites (NFs) as gas-sensitive materials, revealing p-type semiconducting characteristics. The detection of ammonia (NH3) at low concentrations is a significant challenge for chemoresistive gas sensors. Porous Co3O4 nanoflowers were combined with In2O3 nanoparticles to form p-n heterojunctions for NH3 detection. The p-n heterojunction effect and the capability of the sub-valent band to hold vacancies within In2O3 nanoparticles effectively inhibit electron-hole recombination and extend the carrier lifetime. The In2O3/Co3O4 = 0.04 ratio-based gas sensor exhibited excellent selectivity, achieving a low detection limit of 500 ppb for NH3 at 250 °C. The rapid diffusion of gas within the porous Co3O4 NSs and In2O3 nanoparticles accounted for the high response (7.72) and fast response/recovery time (92 s/51 s) of the In2O3/Co3O4-based gas sensor to 10 ppm NH3. This study presents a method for fabricating NH3 gas sensors with trace-level detection capabilities by adjusting the band structure of nanoparticles and three-dimensional metal-oxide nanostructures.

PhDMADBr assisted additive or interface engineering for efficient and stable perovskite solar cells fabricated in ambient air

The fabrication of high-quality perovskite films with low defect density in ambient air is an important approach to enhance the power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In this paper, efficient and stable PSCs were fabricated in ambient air, and p-xylilenediamine bromide (PhDMADBr) assisted additive or interface engineering were carried out to modify perovskite films, which was dispersed into the electron transport layer (ETL) or deposited in the ETL/ perovskite interface. Notably, interaction between PhDMADBr and perovskite layer could reduce defect density and release residual stress of the active layer, which would induce a high-quality perovskite film, and accelerate the transport rate and prolong lifetimes of charge carriers, contributing to the PCE and stability of devices. As a result, compared with the PCE of the control device (22.54 %), the PhDMADBr modified target PSCs exhibited the enhanced PCE of 24.15 % and 23.74 % after additive or interface treatments in ambient air, respectively. Except the improvement of the PCE, PhDMADBr-based devices also presented the enhanced moisture stability. The average efficiency retained the 88 % or 84 % of initial efficiency after 120 h with RH of 40 ± 5 % for additive or interface modification, respectively. In contrast, the PCE of the control devices would decline to 51 % of initial efficiency after storage for 120 h.

Defects analysis of radiation damage mechanism for IMM triple-junction solar cell under 1 MeV electron irradiation

Inverted metamorphic (IMM) GaInP/GaAs/InGaAs rigid triple-junction solar cells under 1 MeV electron irradiation at various fluences were investigated theoretically. By fitting the electrical and optical parameters of solar cells with experimental results at the fluence ranging from 1 × 1014 e cm−2 to 1 × 1015 e cm−2, basic trap information was obtained, and then the minority carrier lifetime and trap concentration of sub-cells at various fluences were also calculated. The defects analysis of IMM triple-junction solar cell presented in this work could help understanding the radiation damage mechanism of 1 MeV electron irradiation.

Theoretical analysis of passively mode-locked semiconductor ring lasers.

In this paper, the theoretical analysis of the passive mode-locked semiconductor ring lasers (PML-SRLs) is investigated based on a travelling wave model. It is found that both the optical confinement factor and the injection current make great contributions to the operation regime and the performance of PML-SRLs. All operation regimes of PML-SRLs are governed by the transient gain-loss balance. Such balance is closely associated with the relationship among the stimulated rate in the semiconductor optical amplifier (SOA), the carrier lifetime in the saturated absorber (SA), and the roundtrip time of the ring resonator. Furthermore, our investigation indicates that the mode-locked state of such PML-SRLs is independent of the passive waveguide, but the performance degrades with the increased waveguide loss or the shortened waveguide length, once the material bandwidth is wide enough. Another discovery is that it is possible to achieve the high energy pulse in the PML-SRL with shortening the passive length and narrowing the gain spectrum meanwhile. Overall, such investigations should benefit designing the required PML-SRLs and achieving the high performance.

Moisture‐Induced High‐Quality Perovskite Film in Air for Efficient Solar Cells

The quality of perovskite light‐harvesting layer is known to be the most critical factor for the performance of perovskite solar cells (PSCs). Herein, a facile ambient air‐aging process (AAP, 20%–30% RH) is adopted to realize the fabrication of high‐quality Cs0.15FA0.75MA0.1PbI3 perovskite films, thereby upgrading device performance. We find that the perovskite crystallinity after AAP for 10 d is greatly intensified, with large grain size and preferred crystal orientation along (110) and (220) planes. Comparative studies on the Ag‐based devices employing the perovskite films upon exposing to different atmospheres, i.e., dry N2, dry O2, N2, and H2O (20%–30% RH) and ambient air (20%–30% RH), demonstrate that H2O molecules in air rather than O2 molecules induce an effective defect passivation that holds the multiple functions in enhancing the quality of perovskite film, inhibiting the nonradiative recombination, prolonging the carrier lifetime, and improving the energy level matching, etc. Moreover, the positive effect of H2O in ambient atmosphere on cell performance is irreversible and remains even if moisture escapes. Finally, the average power conversion efficiency (PCE) of device based on the AAP‐induced film is increased from 18.24 ± 1.49 to 21.34 ± 0.76, with the champion PCE up to 22.60%. Also, the device with AAP exhibits better moisture resistance capability. Herein, it offers a viable AAP‐induced route for the perovskite films with superb optoelectronic properties that can be subsequently extended to the design and construction of other photovoltaic devices for practical application.

Subtraction Descriptors in Machine Learning for Optimizing the Cocatalyst Effect of Cobalt Phosphate on Hematite Photoanodes.

In the quest for sustainable energy solutions, the optimization of the photoelectrochemical (PEC) performance of hematite photoanodes through cocatalysts represents a promising avenue. This study introduces a novel machine learning approach, leveraging subtraction descriptors, to isolate and quantify the specific effects of cobalt phosphate (Co-Pi) as a cocatalyst on hematite's PEC performance. By integrating data from various analytical techniques, including photoelectrochemical impedance spectroscopy and ultraviolet-visible spectroscopy, with advanced machine learning models, we successfully predicted the PEC performance enhancement attributed to Co-Pi. The Gaussian process regression (GPR) model emerged as the most effective, revealing the critical influence of the interfacial resistance, bulk resistance, and interfacial capacitance on the PEC performance. These findings underscore the potential of cocatalysts in improving charge separation and extending charge carrier lifetimes, thereby boosting the efficiency of photocatalytic reactions. This study not only advances our understanding of the cocatalyst effect in photocatalytic systems but also demonstrates the power of machine learning in modifying complex materials and guiding the development of optimized photocatalytic materials. The implications of this research extend beyond hematite photoanodes, offering a generalizable framework for enhancing the photoelectrochemical properties of a wide range of material modifications such as cocatalyst deposition, doping, and passivation.

Bridging-Solvent Strategy for Quasi-Single-Crystal Perovskite Films and Stable Solar Cells.

Controllable fabrication of formamidinium (FA)-based perovskite solar cells (PSCs) with both high efficiency and long-term stability is the key to their further commercialization. However, the diversity of PbI2 complexes and perovskite compositions usually leads to light sensitive PbI2 residues and phase impurities in the film, which can accelerate the device degradation. Here, the crystallization kinetics of FA-based perovskite films are studied and a bridging-solvent strategy is proposed to modulate the reaction kinetics between PbI2 and ammonium salts by prohibiting the formation of undesired intermediates. N-methylpyrrolidone (NMP) solvent is introduced into the PbI2 precursor solution to obtain stable and homogeneous PbI2-NMP complex films. The strong interaction between NMP and formamidinium iodide (FAI) molecules promotes the conversion from PbI2-NMP into (001)-oriented quasi-single-crystal perovskite films with negligible impurities, long carrier lifetime of 1.5µs and a large grain size of 3µm. The optimized PSCs exhibit a high power conversion efficiency of 24.1%, as well as superior shelf stability which maintains 95% initial efficiency after storage in air for 1200h (T95=1200h), and operating stability with T96=300h under continuous working at the maximum power point. This work offers a simple and reproducible method for fabricating phase-pure and uniaxially oriented perovskite films.

Hydrophobic Electron‐Transport Layer for Efficient Tin‐Based Perovskite Solar Cells

AbstractWith excellent biocompatibility, a narrow bandgap, and long thermal carrier lifetime, tin‐based perovskite solar cells (TPSCs) are promising within the solar technology. The fullerene derivative indene‐C60 bisadduct (ICBA) is recognized as the most efficient electron‐transport material for TPSCs, thanks to its suitable band structure. Nevertheless, the limited electron transport capability and susceptibility to moisture penetration of ICBA have hindered the progress of TPSCs. Herein, the study proposes a new hydrophobic electron‐transport layer (ETL) comprising a surface‐anchored non‐fullerene n‐type semiconducting polymer layer, poly (naphthalene diimide‐alt‐dithiophenebezothiadiazole) (PNDI‐BT), in conjunction with ICBA. PNDI‐BT exhibits high electron mobilities, a fitting band structure, robust interaction with Sn‐based perovskites, and exceptional moisture resistance, effectively addressing the shortcomings of ICBA. Consequently, this innovative hydrophobic ETL of PNDI‐BT/ICBA enhances electron transport and protects Sn‐based perovskites from moisture. As a result, the inverted TPSCs with the new hydrophobic ETL achieve an impressive efficiency of 13.90%, surpassing TPSCs with the ICBA layer (12.75%). Moreover, even after 1000 h of storage in ambient atmosphere, the encapsulated TPSC maintains a remarkable 81% of its initial efficiency. This comprehensive study seamlessly integrates the synthesis of non‐fullerene n‐type semiconducting polymer and device fabrication, providing valuable insights into designing cutting‐edge ETL structure for inverted TPSCs.

Atomic imaging and optical properties of InAs/In0.5Ga0.5As0.5Sb0.5 type II superlattice

High-quality III–V quantum structures, advanced epitaxial technologies, and characterization methods are essential to drive the development of infrared optoelectronic materials and devices. As an important component of type II superlattices, InAs/InxGa1−xAsySb1−y would play an important role in the field of high-performance infrared detectors due to their excellent luminescence efficiency and high crystal quality. However, their interfacial characteristics and the associated minority carrier lifetime are still difficult to identify. In this paper, an atomic imaging technique was used to identify the arrangement and distribution of elements of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice. Our results confirm the epitaxy mechanism that the quaternary alloy consists of two kinds of ternary alloy in one monolayer. Moreover, by separating the cation and anion columns in the elementally resolved atomic images of the InAs/In0.5Ga0.5As0.5Sb0.5 superlattice, we demonstrate that the interfacial atomic intermixing is less than one molecular layer thickness. Therefore, benefiting from excellent interface quality, InAs/In0.5Ga0.5As0.5Sb0.5 superlattice exhibited high radiation recombination efficiency in the long-wave infrared band (∼8.5 μm), and longer minority carrier lifetime (∼810 ns at 90 K).

Phenylethylammonium iodide induced “in situ healing” behavior for carbon-electrode basing, hole-conductor-free perovskite solar cells

Previous study showed that blending octylammonium iodide (OAI) in a carbon paste induced a kind of in situ healing effect for carbon-electrode basing, hole-conductor-free, planar perovskite solar cells. Here, the strategy is re-examined by considering another kind of ammonium halide molecule or phenethylammonium iodide (PEAI). It is observed that, after moderate PEAI blending, power conversion efficiency of devices rises from 11.56 (±0.82)% to 15.77 (±0.53)% (championed at ∼17.9%), with open-circuit voltage increasing from 969 (±28) to 1033 (±13) mV, and fill factor increasing from 51.17 (±2.68)% to 65.71 (±1.36)%. The improved device efficiency is due to the retarded charge recombination and the improved charge transfer processes. Transient photovoltage/photocurrent decay curve tests show that, after PEAI blending, lifetime of charge carriers in device increases from 3.21 to 5.67 μs, while the charge extraction time decreases from 2.99 to 2.18 μs. Moreover, built-in potential rises according to the Mott–Schottky study. A designated “penetration-reaction” test reveals that PEAI could also induce the in situ healing effect, which accounts for the improved charge transfer/recombination processes. The study could tell the universality of this strategy to certain extent.

The effects of different anode manufacturing methods on deep levels in 4H-SiC p+n diodes

The manufacture of bipolar junctions is necessary in many 4H-SiC electronic devices, e.g., junction termination extensions and p+in diodes for voltage class >10 kV. However, the presence of electrically active levels in the drift layer that act as minority charge carrier lifetime killers, like the carbon vacancy (VC), undermines device performance. In the present study, we compared p+n diodes whose anodes have been manufactured by three different methods: by epitaxial growth, ion implantation, or plasma immersion ion implantation (PIII). The identification of the electrically active defects in the drift layers of these devices revealed that a substantial concentration of VC is present in the diodes with epitaxial grown or ion implanted anode. On the other hand, no presence of VC could be detected when the anode is formed by PIII and this is attributed to the effects of strain in the anode region. Our investigation shows that PIII can be a useful technique for the manufacture of bipolar devices with a reduced concentration of lifetime killer defects.

Self‐Powered Graphene/Black‐Ge Photodetectors Enhanced by Simultaneous Nanotexturing and Self‐Passivation

AbstractBlack germanium (Ge) exhibits exceptional light absorption, holding significant promise for optoelectronic applications. However, achieving self‐powered photodetection performance in black Ge is challenging due to its high surface recombination rate. Herein, this challenge is addressed by demonstrating self‐powered Graphene (Gr)/black‐Ge Schottky photodiodes, achieved through simultaneous nanotexturing and high‐quality self‐passivation. This approach involves utilizing reactive ion etching with Cl2 and BCl3 to achieve Cl‐passivated black Ge. Optical analysis reveals excellent optical characteristics in both Cl2‐treated and BCl3‐treated samples, including a high aspect ratio of 1.9 and a low reflectance of 1.5%. Notably, the Cl2‐treated black Ge exhibits a higher carrier lifetime of 20.4 µs compared to the 11.7 µs lifetime of the BCl3‐treated black Ge, attributed to the self‐passivation induced by Cl2 plasma, effectively mitigating defects. Surface composition analysis further confirms the substantial role of Cl in passivation. Significantly, these improved properties translate into notable advancements in device performance, including an enhancement in responsivity from 21 to 276 mA W−1 when compared to planar Gr/Ge devices. These findings underscore the potential of Cl2 RIE for developing high‐performance Ge‐based optoelectronic devices.

Facile construction of SPR effect assisted Bi2O2CO3/Bi/BiOCl Z-scheme heterostructure for robust photocatalytic decontamination of RhB

A ternary Bi2O2CO3/Bi/BiOCl Z-scheme heterostructure with an ordered flower-like structure was synthesized by controlling KCl content using a facile solvothermal technique, and the photodegradation performance of RhB was investigated in detail. The photocatalytic results suggested that the Bi2O2CO3/Bi/BiOCl manifested an attractive photodegradation rate with 99.20 % of removal efficiency within 20 min of irrigation. The main reason was credited to the SPR effect of metallic Bi and the construction of Z-scheme heterojunction, endowing enhanced adsorption ability of visible light, long lifetime of charge carriers, and fast interfacial electron flow. Furthermore, the degradation pathways towards RhB were also elaborated via LC–MS. A possible photocatalytic mechanism was explored by combining the radicals quench experiments, ESR tests with energy band structures. The study will supply a potential candidate for the remediation of natural RhB wastewater.

Carboxymethyl-β-cyclodextrin functionalized TiO2@Fe3O4@RGO magnetic photocatalyst for efficient photocatalytic degradation of tetracycline under visible light irradiation

In this study, a novel magnetic photocatalyst, carboxymethyl-β-cyclodextrin functionalized titanium dioxide@Fe3O4@reduced graphene oxide (CMCD-TiO2@Fe3O4@RGO) was successfully fabricated by a facile hydrothermal synthesis method. Raman spectroscopy, XRD, BET, FT-IR, VGM, XPS, TGA, SEM, EDS and TEM were used to characterize the photocatalysts. The photocatalytic degradation behavior of tetracycline (TC) was investigated under 420 nm light wavelengths, and the reaction mechanism was interpreted. Furthermore, the stability and reusability of CMCD-TiO2@Fe3O4@RGO were assessed. The outcomes showed that CMCD-TiO2@Fe3O4@RGO possessed higher photocatalytic activity compared with TiO2@Fe3O4@RGO, TiO2@Fe3O4 and TiO2. Under continuous irradiation at 420 nm light for 60 minutes, CMCD-TiO2@Fe3O4@RGO achieved a TC degradation efficiency of 83.3 % at a concentration of 20 mg/L. The kinetic constant for the photocatalytic degradation of TC by CMCD-TiO2@Fe3O4@RGO was determined to be 0.459 mg L−1·min−1, which was 1.49 times higher than that of TiO2@Fe3O4. The main reactive oxygen species contributing to TC degradation were determined to be ·O2- and h+. The presence of RGO and CMCD is beneficial for the adsorption of TC on the photocatalyst. Furthermore, the transfer of photo-generated electrons from the semiconductor to the RGO suppresses electron-hole recombination and enhances carrier lifetime, thereby improving photocatalytic degradation efficiency. Remarkable recyclability and stability were observed in CMCD-TiO2@Fe3O4@RGO, with only a 10.4 % reduction in TC removal after five cycles.

Study of charge transport in cesium lead bromide perovskite quantum dots and PCPDTBT composites: an application to photosensitive FETs

This work investigates the optical, structural, and photo-physical properties of PCPDTBT/cesium lead bromide (CsPbBr3) perovskite quantum dots (QDs) composite for optoelectronic devices. The composite was prepared by processing the PCPDTBT and CsPbBr3 QDs via the solution blending method. Incorporating CsPbBr3 QDs with different weight % (wt%) ratio in PCPDTBT influences its optoelectronic properties. UV–vis absorption spectroscopy, photoluminescence (PL), and atomic force microscopy measurements were used to analyze their optical and morphological properties. We observed that incorporating 4 wt% QDs in PCPDTBT enhanced its light absorption and charge transfer properties. Increased carrier lifetime for PCPDTBT/QDs (4 wt%) was observed from PL decay measurements. Further, we fabricated the field effect transistors (FETs) of pristine PCPDTBT and PCPDTBT/CsPbBr3 QDs composite (4 wt%) to study their electronic and charge transfer features. Significant variation in source-to-drain current (IDS) and carrier mobility has been observed. A substantial increased output current was observed for composite FET than pristine PCPDTBT-based FET due to charge transfer from QDs to PCPDTBT. Both PCPDTBT and PCPDTBT/CsPbBr3 QDs-based FET show enhanced current with illumination, which could be attributed to the photo-generated charge carriers.

Intraband Cooling and Auger Recombination in Weakly to Strongly Quantum-Confined CsPbBr3 Perovskite Nanocrystals.

Semiconductor nanocrystals (NCs) with size-tuned energy gaps present unique and desirable properties for optoelectronic applications. Recent synthetic advancements offer routes to spheroidal CsPbBr3 perovskite NCs in the strong quantum confinement regime with narrow size dispersion. Using tunable femtosecond laser pulses, we examine intraband carrier relaxation using transient absorption spectroscopy and show that, across the transition from weak to strong confinement, hot carrier lifetime increases compared to larger bulk-like particles. However, further increases of confinement subsequently lead to a reduction of the hot carrier lifetime and increase of the non-radiative Auger recombination rate. Finally, we show that hot carrier lifetimes increase as a function of excess energy above the band gap less sensitively under high confinement in comparison to the bulk. Understanding such unique trends is important for maximizing hot carrier lifetimes for use in next-generation hot carrier devices as well as evaluating the transition from weak to strong confinement.

Design of MoO3 Porous Back Contact for High Efficiency CZTSSe Thin-film Solar Cells

The introduction of in-situ anodized MoO3 porous arrays with tailored structural parameters as the rear interface contact has a positive impact on enhancing the solar cell performance. The optimized device efficiency increased from 6.31% to 9.00% (in reference to molybdenum-based cells), resulting in a 32% increase in JSC and a 64% increase in FF. The results indicate that at a 10V oxidation voltage, the MoO3 pore size is relatively larger, facilitating the formation of a well-interpenetrating structure and contact interface with CZTSSe. In turn, assists in carrier interface separation and transfer, effectively suppressing the recombination of separated carriers. It extends carrier lifetime, reduces band tailing effects, and lowers urbach energy, thus improving the overall performance of CZTSSe devices.

Self‐Regulated Growth of Large‐Grain Sb2S3 Thin Films for High‐Efficiency Solar Cells

AbstractAntimony sulfide (Sb2S3) has attracted extensive attention due to its excellent photoelectric characteristics, including a high absorption coefficient (α > 104 cm−1) and a suitable bandgap (≈1.7 eV). However, due to its Q1D (quasi‐1D) structure, numerous deep‐level defects are identified in the Sb2S3 film, limiting the device's performance, and necessitating more efforts to overcome this situation. In this context, an ethanol solvent‐assisted chemical bath deposition (S‐CBD) strategy, a novel high‐quality thin film manufacturing technique is presented that modifies the supersaturation of the precursor solution by varying the boiling point and solvent polarity. This approach enables the effective regulation of the correlation between the crystal nucleation and growth rates, resulting in Sb2S3 films with large grains (≈4.25 µm, 37.5% ethanol), excellent crystallinity, well‐oriented structures (TC(211)/TC(020) = 2.39), low defect density, and prolonged carrier lifetimes (τAve ≈ 12.1 ns). Consequently, the final Sb2S3‐based solar device (FTO/CdS/Sb2S3/Spiro‐OMeTAD/Au) shows significant improvements in both FF (61.63%) and JSC (17.61 mA cm−2), yielding an excellent power conversion efficiency (PCE) of 7.84%. This research gives particular insights into the growth mechanism of high‐quality Sb2S3 thin films by CBD method as well as a potential route for enhancing Sb2S3 solar cell performance.

Macrocyclic thiol ligand additive engineering for stable and efficient perovskite solar cells

Perovskite solar cells have a rapid development speed and excellent prospects, but still face performance and stability problems for practical applications. Excessive Pb2+ defects often accompany the preparation of perovskite, which greatly affect the performance and stability of perovskite solar cells. Herein, a macrocyclic thiol ligand (DXPSH) is introduced as an additive for organic amine salt. It effectively reduces the defect density of perovskite, induces better crystal orientation of perovskite, and improves carrier lifetime. As a result, the optimized DXPSH-modified PSCs achieves a maximum power conversion efficiency of 24.03 % and good long-term stability in ambient air.

4-Methoxy phenethylammonium halide salts for surface passivation of perovskite films towards efficient and stable solar cells

Surface defects-mediated non-radiative charge recombination in polycrystalline perovskite films has been widely acknowledged to be responsible for the undesired open-circuit voltage (VOC) deficit, which is still a great challenge for perovskite solar cells (PSCs) to achieve the Shockley-Queisser efficiency limit. Herein, we report the use of 4-methoxy phenethylammonium halide salts (4-MeO-PEAX, X = I, Br, Cl) on the surface of formamidinium-cesium (FACs) perovskite films for surface passivation. The impact of halogen species in 4-MeO-PEAX on the quality of FACs perovskite films and device performance are comparatively investigated. We find that the prepared FACs perovskite films demonstrate dramatically reduced defect density and surface roughness, improved crystallinity, preferred (001) orientation and prolonged carrier lifetime after the post-treatment by 4-MeO-PEACl. Consequently, the 4-MeO-PEACl post-processed p-i-n PSCs have achieved a significantly improved power conversion efficiency of 22.63 % and VOC of 1.13 V. The unencapsulated devices post-treated with 4-MeO-PEACl maintained 90 %, 88 % and 84 % of their initial efficiencies, after being thermally stressed at 65 ℃ under dark for 312 h, stored in ambient air for 720 h and operated under continuous 1 sun equivalent illumination with maximum power point tracking at 50 ℃ for 1000 h, respectively.