Carrier Lifetime Research Articles

Photoresponse Design in Metal Oxide Semiconductor TFTs toward Diverse Applications: Display Drivers, Photodetectors, and Optoelectronic Synapses.

Different application domains impose diverse and often conflicting requirements on the optoelectronic performance of metal oxide semiconductor (MOS) thin-film transistors (TFTs). These varying demands present substantial challenges in the selection of TFT materials and the optimization of device performance. This study begins by examining three primary application areas for TFTs: display drivers, photodetectors, and optoelectronic synapses. A comparative analysis of the optoelectronic properties is conducted among various MOS TFTs fabricated by magnetron sputtering, including indium-gallium-zinc-oxide (IGZO, In/Ga/Zn = 1:2:1), indium-gallium-oxide (IGO, In/Ga = 1:1), indium-zinc-oxide (IZO, In/Zn = 1:1), indium oxide (In2O3), and zinc oxide (ZnO). The investigation reveals the significant impact of material selection on key performance metrics essential for these applications, such as photoresponse, the decay rate of photocurrent (Iph), and negative bias illumination stress (NBIS). Additionally, a comprehensive summary of the applicable domains for each type of TFT is provided. The study also explores the correlation between activation energy (Ea) and TFT performance, indicating that higher Ea is associated with a stronger persistent photoconductivity (PPC) effect but poorer stability. Furthermore, the content of oxygen vacancy (VO) shows a positive correlation with the decay rate of Iph. Lastly, the photogenerated carrier lifetime (τ) is derived and compared among the five MOS materials, revealing the potential applications and performance characteristics of each in optoelectronic devices. The findings offer a nuanced understanding of the intrinsic relationships between material properties, defect states, and photoelectric performance, thereby guiding the selection and optimization of channel layer materials for specific application requirements.

Enhanced Efficiency and Stability of Tin Halide Perovskite Solar Cells Through MOF Integration.

Tin halide perovskites are promising candidates for lead-free perovskite solar cells due to their ideal bandgap and high charge-carrier mobility. However, poor crystal quality and rapid degradation in ambient conditions severely limit their stability and practical applications. This study demonstrates that incorporating UiO-66, a zirconium-based MOF, significantly enhances the performance and stability of tin halide perovskite solar cells (TPSCs). The unique porous structure and abundant carboxylate groups of UiO-66 improve the crystallinity and film quality of FASnI₃, reduce defect density, and prolong charge carrier lifetimes. Consequently, the power conversion efficiency (PCE) of UiO-66-integrated TPSCs increases from 11.43% to 12.64%, and the devices maintain over 90% of their initial PCE after 100 days in a nitrogen glovebox. These findings highlight the potential of UiO-66 in addressing the efficiency and stability challenges of tin halide perovskites.

Effectively Enhanced Photocatalytic Performance of BP/BiOBr 2D/2D Z-Scheme Heterojunction

Black phosphorus (BP) is a novel two-dimensional (2D) material with remarkable potential for use in environmental remediation and energy conversion. However, the practical application of BP is significantly limited by its low catalytic efficiency and poor structural stability. In this study, a Z-scheme BP/BiOBr 2D/2D heterojunction was fabricated using a simple solution reaction method at room temperature. The BP/BiOBr heterojunction exhibited significantly enhanced photocatalytic performance in the degradation of various organic pollutants and the production of hydrogen under visible light irradiation. This improved activity can be attributed to the efficient separation of photogenerated charges and the extended lifetime of charge carriers within the heterojunction. The durability and structural stability of the BiP-10 heterojunction were demonstrated through cycling tests, which maintained high photocatalytic efficiency over multiple uses. This study presents a promising approach to the development of BP-based photocatalytic materials for sustainable environmental and energy applications.

Silver single atoms and nanoparticles on floatable monolithic photocatalysts for synergistic solar water disinfection

Photocatalytic water disinfection technology is highly promising in off-grid areas due to abundant year-round solar irradiance. However, the practical use of powdered photocatalysts is impeded by limited recovery and inefficient inactivation of stress-resistant bacteria in oligotrophic surface water. Here we prepare a floatable monolithic photocatalyst with ZIF-8-NH2 loaded Ag single atoms and nanoparticles (AgSA+NP/ZIF). Atomically dispersed Ag sites form an Ag−N charge bridge, extending the lifetime of charge carriers and thereby promoting reactive oxygen species (ROS) generation. The photothermal effect of the plasmonic Ag nanoparticles reduces the bacterial resistance to ROS and impairs DNA repair capabilities. Under sunlight irradiation, the synergistic effect of Ag single atoms and nanoparticles enables 4.0 cm2 AgSA+NP/ZIF to achieve over 6.0 log inactivation (99.9999%) for the stress-resistant Escherichia coli (E. coli) in oligotrophic surface water within 30 min. Furthermore, 36 cm2 AgSA+NP/ZIF is capable of disinfecting at least 10.0 L of surface water, which meets the World Health Organization (WHO) recommended daily per capita drinking water allocation (8.0 L). This study presents a decentralized and sustainable approach for water disinfection in off-grid areas.

Effects of Intrinsic Defects on the Carrier Lifetime in CdZnTe: Insights from Ab Initio Calculations.

CdZnTe (CZT) has garnered substantial attention due to its outstanding performance in room-temperature semiconductor radiation detectors, where carrier transport properties are critical for assessing the detector performance. However, due to the complexities of crystal growth, CZT is prone to defects that affect carrier lifetime and mobility. To investigate how defects affect nonequilibrium carrier transport, nonadiabatic molecular dynamics (NAMD) is employed to examine six types of intrinsic defects and their impact on electron-hole (e-h) recombination. The findings reveal that Te substitution at the Cd site (TeCd) and Te interstitial (Tei) defects expedite recombination by introducing intermediate energy levels. The coupling of new energy levels in Te vacancy (VTe) with the conduction band minimum (CBM) slows down electron release and results in an extended recombination time. Cd substitution at the Te site (CdTe) and Cd interstitial (Cdi) defects enhance nonadiabatic coupling (NAC) to accelerate the recombination. In contrast, Cd vacancy (VCd) diminishes NAC through weakening carrier coupling with high-frequency phonons and leads to a deceleration of the recombination rate. Overall, the intrinsic defects may change electron structures to vary NAC, which is critical for the recombination rate. It is believed that this research may benefit the understanding of defects on the carriers' lifetime in CZT and provide hints for further optimizing the performance of CZT material in nuclear radiation detection.

Significant Efficiency Enhancements in Non-Y Series Acceptors by the Addition of Outer Side Chains.

Most current highly efficient organic solar cells utilize small molecules like Y6 and its derivatives as electron acceptors in the photoactive layer. In this work, a small molecule acceptor, SC8-IT4F, is developed through outer side chain engineering on the terminal thiophene of a conjugated 6,12-dihydro-dithienoindeno[2,3-d:2',3'-d']-s-indaceno[1,2-b:5,6-b']dithiophene (IDTT) central core. Compared to the reference molecule C8-IT4F, which lacks outer side chains, SC8-IT4F displays notable differences in molecule geometry (as shown by simulations), thermal behavior, single-crystal packing, and film morphology. Blend films of SC8-IT4F and the polymer donor PM6 exhibit larger carrier mobilities, longer carrier lifetimes, and reduced recombination compared to C8-IT4F, resulting in improved device performance. Binary photovoltaic devices based on the PM6:SC8-IT4F films reveal an optimal efficiency over 15%, which is one of the best values for non-Y type small molecule acceptors (SMAs). The resultant devices also show better thermal and operational stability than the control PM6:L8-BO devices. SC8-IT4F and its blend exhibit a higher relative degree of crystallinity and π coherence length, compared to C8-IT4F samples, beneficial for charge transport and device performance. The results indicate that outer side chain engineering on existing small electron acceptors can be a promising molecular design strategy for further pursuing high-performance organic solar cells.

Homogeneously Blended Donor and Acceptor AgBiS2 Nanocrystal Inks Enable High‐Performance Eco‐Friendly Solar Cells with Enhanced Carrier Diffusion Length

AbstractColloidal semiconductor nanocrystals (NCs) have garnered significant attention as promising photovoltaic materials due to their tunable optoelectronic properties enabled by surface chemistry. Among them, AgBiS2 NCs stand out as an attractive candidate for solar cell applications due to their environmentally friendly composition, high absorption coefficients, and low‐temperature processability. However, AgBiS2 NC photovoltaics generally exhibit lower power conversion efficiency (PCE) compared to other NC‐based devices, primarily due to numerous surface traps that serve as recombination sites, leading to a short diffusion length for free carriers. To address this challenge, this work develops donor and acceptor blended (D/A) AgBiS2 films. Through ligand modulation, this work formulates acceptor and donor AgBiS2 NC inks with suitable electrical band alignment for charge separation, while ensuring that they are fully miscible in the same solvent. This enabled the fabrication of high‐quality, thickness‐controllable D/A‐blended junction films. This work finds that this approach effectively facilitates carrier separation, leading to an enhanced carrier lifetime and diffusion length. As a result, using this approach, this work achieves AgBiS2 films that are twice as thick in solar cell applications compared to conventional devices, leading to improvements in current density and a solar cell PCE of 8.26%.

The theoretical investigation of the g-C3N4/ZnS heterojunction for photocatalytic applications.

Graphitic carbon nitride (g-C3N4) is a useful photocatalyst applied in various areas. However, it has some disadvantages that limit its applications. Therefore, doping and the construction of a heterojunction are beneficial methods to overcome these drawbacks. ZnS is one of the photocatalysts that can be combined with g-C3N4. The sulfur vacancy defect in ZnS enhances its ability to adsorb visible light compared to bare ZnS. In this work, we theoretically investigated bulk g-C3N4 (g-C3N4-B), monolayer g-C3N4 (g-C3N4-M), ZnS, and defective ZnS (ZnS-D) using the SIESTA package. Subsequently, the position of the conduction band minimum (CBM) and valence band maximum (VB) of g-C3N4-B and g-C3N4-M were plotted relative to the CBM and VBM of ZnS-B and ZnS-D. The results showed that the g-C3N4/ZnS heterojunction is more suitable than g-C3N4/ZnS-D. This heterojunction is a Z-scheme type, which increases the lifetime of the carriers. On the other hand, it is a narrow gap semiconductor that can be used in thermoelectric devices, and the value of the Seebeck coefficients confirms that the heterojunction enhances the thermoelectric properties of the photocatalysts. Our results demonstrate that the Z-scheme mechanism enhances the lifetime of carriers and thermoelectric properties.

Temperature‐Dependent Charge‐Carrier Dynamics in Lead‐Halide Perovskites: Indications for Dynamic Disorder Dominated Scattering Mechanism

AbstractLead‐halide perovskites have emerged as a promising material class in light‐harvesting and light‐emitting applications due to their exceptional semiconductor properties. Nonetheless, crucial semiconducting properties such as the charge carrier scattering mechanism and its impact on recombination dynamics are not well studied. Here, five different lead‐halide perovskite compositions are systematically examined to determine their temperature‐dependent mobility, and the prevalent scattering mechanisms involved are identified. Dynamic disorder is proposed to be the predominant scattering mechanism at room temperature and above, as evidenced by a change in the power‐law Tm. Notably, the onset temperature for this behavior varies with the perovskite composition. Additionally, it is found that this scattering process coincides with changes in fast‐trapping behavior in MAPbI3 perovskite, which in turn alters recombination dynamics such as carrier lifetime and diffusion length. These results suggest that this scattering mechanism contributes to the defect tolerance of perovskites, providing valuable insights for further investigations.

Constructing Interfacial B-P Bonding Bridge to Promote S-Scheme Charge Migration within Heteroatom-Doped Carbon Nitride Homojunction for Efficient H2O2 Photosynthesis.

The emerging step (S)-scheme heterojunction systems became a powerful strategy in promoting photogenerated charge separation while maintaining their high redox potentials. However, the weak interfacial interaction limits the charge migration rate in S-scheme heterojunctions. Herein, we construct a unique S-scheme carbon nitride (CN) homojunction with boron (B)-doped CN and phosphorus (P)-doped CN (B-CN/P-CN) for hydrogen peroxide (H2O2) photosynthesis. The B-CN/P-CN nanosheet composites revealed extensively tight interfacial contact, improved visible-light harvesting, and reduced carrier lifetime. The structural investigation results also indicate that the interfacial chemical B-P bonding is formed between B-CN and P-CN nanosheets, inducing an accelerated interfacial S-scheme charge migration. Density functional theory calculations further clarify the S-scheme charge transfer mechanism. Consequently, the 2e- oxygen reduction reaction was the predominant pathway of H2O2 production, facilitated by the B-CN/P-CN homojunction. The optimal H2O2 yield rate reached 2199.5 μmol L-1 h-1 over the B-CN/P-CN homojunction (S3) photocatalyst under monochromatic LED irradiation, increasing 2-8 times as against most of the C3N4 photocatalysts. This study highlights the crucial role of interfacial charge transfer between heterojunction/homojunction materials, accompanied by an unveiling reaction mechanism for solar-energy conversions.

Anti-reflective and luminescent GaAs/AlGaAs core–shell nanowires on Si wafer with 1 ns carrier lifetime up to 400 K

We investigated the structural and optical properties of GaAs/Al0.8Ga0.2As core–shell nanowires (NWs) grown on a 2-in. Si wafer. The NWs exhibit low reflectance (<2%) across the visible to near-infrared range, attributed to their complex structure, intrinsic GaAs absorption, and a uniform NW density of approximately 3 × 108 cm−2 with an average length of 5 μm. Optical analyses based on Kubelka–Munk transformation and Tauc plot revealed minimal deviation between the estimated bandgap and the photoluminescence (PL) peak position. Temperature-dependent PL measurements between 300 and 400 K showed a weak intensity reduction and a characteristic temperature of 170 K, indicating stable emission properties within this range. Time-resolved-PL measurements demonstrated carrier lifetimes exceeding 1 ns up to 400 K, with a surface recombination velocity comparable to high-quality GaAs/AlGaAs NWs. These findings provide key insights into the optical performance and thermal stability of the NWs, highlighting their potential for optoelectronic devices operating at elevated temperatures.

Synergetic Interface and Bulk Defects Modification with Identical Organic Molecule for Efficient Inverted Perovskite Solar Cells.

Recent progress in inverted perovskite solar cells (IPSCs) mainly focused on NiOx modification and perovskite (PVK) regulation to enhance efficiency and stability. However, most works address only monofunctional modifications, and identical molecules with the ability to simultaneously optimize NiOx interface and perovskite bulk phase have been rarely reported. This work proposes a dual modification approach using 4-amino-3,5-dichlorobenzotrifluoride (DCTM) to optimize both NiOx upper interfaces and reduction of bulk defects in perovskite. Amino group in DCTM increases the Ni3+/Ni2+ ratio in NiOx, thereby increasing the conductivity and optimizing the energy alignment. Additionally, DCTM fills Pb2+ and I- vacancies in perovskite, which improves the vertical orientation of perovskite grains and subsequently reduces nonradiative recombination, thereby achieving the increased carrier lifetime. PVK modified by DCTM exhibits enhanced energy level alignment with the electron transport layer, while femtosecond transient absorption (TA) spectroscopy confirms that DCTM facilitates efficient carrier transport, leading to high-performance IPSCs. The optimized IPSCs achieve a maximum efficiency of 22.8% with a reduced hysteresis (0.7%). Moreover, the unencapsulated device preserves over 80% of its initial power conversion efficiency (PCE) after 1000 h stored in air at 30% relative humidity. This dual modification strategy of monomolecular offers a straightforward solution for interface optimization and provides new insights into selecting aniline-derived molecules for high-performance IPSCs.

Colloidal Nanoparticles Hold Elementary Charge in Nonpolar Solvent.

The net charge of individual nanoparticles in nonpolar solvents plays a critical role in their intrinsic properties like charge carrier lifetime, electron transport, and interparticle interactions. However, there is a long-standing belief that the oil-dispersed nanoparticles inherently possess no net charge. This work presents an approach for directly quantifying the net charge of individual nanoparticles. We employ an alternating electric field coupled with in situ observation under an optical microscope to analyze the force and motion of sub-50 nm silver nanoparticles. This technique directly reveals that around 1-10% of these colloidal nanoparticles carry a single elementary charge in nonpolar solvents, while the majority remain essentially neutral. This represents the first quantitative measurement of a single nanoparticle's charge in a nonpolar solvent.

Band Tailoring Enabled Perovskite Devices for X-Ray to Near-Infrared Photodetection.

Perovskite semiconductors have shown significant promise for photodetection due to their low effective carrier masses and long carrier lifetimes. However, achieving balanced detection across a broad spectrum-from X-rays to infrared-within a single perovskite photodetector presents challenges. These challenges stem from conflicting requirements for different wavelength ranges, such as the narrow bandgap needed for infrared detection and the low dark current necessary for X-ray sensitivity. To address this, this study have designed a type-II FAPbI3 perovskite-based heterojunction featuring a large energy band offset utilizing narrow bandgap tellurium (Te) semiconductor. This innovative design broadens the detection range into the infrared while simultaneously reducing dark current noise. As-designed device allows for the detection of near infrared band, achieving a detectivity of 6.8 × 109 Jones at 1550 nm. The low dark current enables X-ray sensitivity of up to 1885.1 µC Gy⁻¹ cm⁻2. First-principles calculations confirm the type-II band structure alignment of the heterojunction, and a self-driven response behavior is realized. Moreover, this study have developed a scalable 40 × 1 sensor array, demonstrating the potential for wide-spectrum imaging applications. This work is expected to advance the application of perovskite-based wide-spectrum devices.

Machine learning-based laser heterodyne photothermal displacement method: simultaneous estimation of silicon thermal diffusivity and carrier lifetime

Abstract The laser heterodyne photothermal displacement (LH-PD) method, a recently developed photothermal technique, enables measurement of absolute surface displacements, which are otherwise challenging to measure with other photothermal methods. This method offers significant potential for quantifying physical properties that are difficult to achieve with traditional photothermal methods. In this study, we aimed to estimate the thermal diffusivity and carrier lifetime of Si using a machine learning model based on the time variation of the displacement obtained using the LH-PD method. By leveraging the machine learning model, we generated predictive mappings of thermal diffusivity and carrier lifetime of a pattern-etched Si wafer from the displacement mappings. Furthermore, our findings demonstrated that fine-tuning the model enabled accurate predictions of the carrier lifetime. While traditional simulations require tens of hours to estimate the material parameters, machine learning reduced this process to only a few seconds.

Dynamics of Photoinduced Charge Carrier and Photothermal Effect in Pulse-Illuminated Narrow Gap and Moderate Doped Semiconductors

When a sample of semiconducting material is illuminated by monochromatic light, in which the photon energy is higher than the energy gap of the semiconductor, part of the absorbed electromagnetic energy is spent on the generation of pairs of quasi-free charge carriers that are bound by Coulomb attraction. Photo-generated pairs diffuse through the material as a whole according to the density gradients established, carrying part of the excitation energy and charge through the semiconducting sample. This energy is indirectly transformed into heat, where the excess negatively charged electron recombines with a positively charged hole and causes additional local heating of the lattice. The dynamic of the photoexcited charge carrier is described by a non-linear partial differential equation of ambipolar diffusion. In moderate doped semiconductors with a low-level injection of charge carriers, ambipolar transport can be reduced to the linear parabolic partial differential equation for the transport of minority carriers. In this paper, we calculated the spectral function of the photoinduced charge carrier distribution based on an approximation of low-level injection. Using the calculated distribution and inverse Laplace transform, the dynamics of recombination photoinduced heat sources at the surfaces of semiconducting samples were studied for pulse optical excitations of very short and very long durations. It was shown that the photoexcited charge carriers affect semiconductor heating depending on the pulse duration, velocity of surface recombination, lifetime of charge carriers, and their diffusion coefficient.

Enhanced broadband quantum efficiency in LWIR T2SL detectors with guided-mode resonance structure.

Type-II superlattice (T2SL) detectors are emerging as key technologies for next-generation long-wavelength infrared (LWIR) applications, particularly in the 8-14 µm range, offering advantages in space exploration, medical imaging, and defense. A major challenge in improving quantum efficiency (QE) lies in achieving sufficient light absorption without increasing the active layer (AL) thickness, which can elevate dark current and complicate manufacturing. Traditional methods, such as thickening the absorber, are limited by the short carrier lifetime in T2SLs, necessitating alternative solutions. In this study, we introduced a guided-mode resonance (GMR) structure into T2SL LWIR detectors to enhance QE while maintaining a thin AL for efficient carrier collection. The GMR structure was fabricated by introducing a grating array on the surface of the detector and an Au mirror beneath the absorber. This configuration enhanced light trapping, which introduced additional resonance modes. The optimized grating design, with a 5 µm period and a fill factor of 0.6, significantly increased absorption, as predicted by finite-difference time-domain (FDTD) simulations and confirmed experimentally. The GMR-enhanced T2SL detector demonstrated a 2.58-fold improvement in QE over conventional LWIR detectors and a 1.33-fold increase compared to Fabry-Pérot (FP) resonance-based detectors in the 6-11 µm range. Despite exhibiting an almost identical dark current density, the GMR LWIR detector demonstrated superior performance, featuring a broader cut-off wavelength of 9.3 µm and higher QE compared to FP LWIR detectors.

Impact of mercury vacancy states on Shockley–Read–Hall recombination in narrow gap HgCdTe

Abstract Technologically relevant narrow gap Hg1-xCdxTe is known to contain a considerable amount of mercury vacancies that supposedly degrade carrier lifetimes. Using semiclassical approach with no adjustable parameters, we calculate capture coefficients for acceptor states with different binding energy. Resulting Shockley–Read–Hall recombination times agree well with the experimental data and suggest that operating temperature of Hg1-xCdxTe detectors with ~ 20 µm cutoff can be elevated above 77 K.

Impact of mercury vacancy states on Shockley–Read–Hall recombination in narrow gap HgCdTe

Abstract Technologically relevant narrow gap Hg1-xCdxTe is known to contain a considerable amount of mercury vacancies that supposedly degrade carrier lifetimes. Using semiclassical approach with no adjustable parameters, we calculate capture coefficients for acceptor states with different binding energy. Resulting Shockley–Read–Hall recombination times agree well with the experimental data and suggest that operating temperature of Hg1-xCdxTe detectors with ~ 20 µm cutoff can be elevated above 77 K.

Simultaneous passivation of surface and bulk defects in all‐perovskite tandem solar cells using bifunctional lithium salts

AbstractAll‐perovskite tandem solar cells have garnered considerable attention because of their potential to outperform single‐junction cells. However, charge recombination losses within narrow‐bandgap (NBG) perovskite subcells hamper the advancement of this technology. Herein, we introduce a lithium salt, lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), for modifying NBG perovskites. Interestingly, LiTFSI bifunctionally passivates the surface and bulk of NBG by dissociating into Li+ and TFSI− ions. We found that TFSI− passivates halide vacancies on the perovskite surface, reducing nonradiative recombination, while Li+ acts as an interstitial n‐type dopant, mitigating the defects of NBG perovskites and potentially suppressing halide migration. Furthermore, the underlying mechanism of LiTFSI passivation was investigated through the density functional theory calculations. Accordingly, LiTFSI facilitates charge extraction and extends the charge carrier lifetime, resulting in an NBG device with power conversion efficiency (PCE) of 22.04% (certified PCE of 21.42%) and an exceptional fill factor of 81.92%. This enables the fabrication of all‐perovskite tandem solar cells with PCEs of 27.47% and 26.27% for aperture areas of 0.0935 and 1.02 cm2, respectively.image