Search Results (145)

Accurate real-time dosimetry is key in megavoltage radiotherapy; however, many detectors require external biasing or complex instrumentation. This study evaluated thin-film CdTe solar cells operating in photovoltaic (zero-bias) mode as medical dosimeters. Superstrate ITO/CdS/CdTe/Cu/Au devices were fabricated and irradiated with 6-MV photons from a clinical linear accelerator to 20 kGy cumulative dose. Electrical and dosimetric properties were assessed based on AM 1.5 current–voltage measurements, external quantum efficiency (EQE), dose linearity, dose-rate dependence, field-size dependence, percentage depth dose (PDD), and one-month reproducibility. With increasing dose (5–20 kGy), the open-circuit voltage and fill factor decreased by ~2–3%, the short-circuit current density by ~10%, retaining ~87% initial efficiency. Series and shunt resistances were stable, while EQE decreased uniformly (~5%), indicating degradation mainly from increased nonradiative recombination. Dose–signal linearity remained intact, and post-irradiation sensitivity loss was corrected with a single calibration factor. Dose-rate dependence was minor; low reverse bias (~3–7 V) enhanced response without nonlinearity. Field-size and PDD responses agreed with ionization chamber data within ~1%, and weekly stability was within ~1%. Parallel stacking of two cells increased signal nearly linearly. CdTe solar-cell detectors thus enable zero-bias, real-time, stable, and scalable dosimetry and strongly agree with reference standards. Full article

The chemical identity of oxygen species plays a decisive role in determining the optical stability of halide perovskite QD films. Here, real-time in situ spectroscopic monitoring, together with steady-state and time-resolved photoluminescence measurements, is utilized to differentiate the effects of molecular oxygen and plasma-activated oxygen species on CsPbBr₃ QD films. The films maintain nearly unchanged emission intensity, spectral profile, and carrier lifetimes when stored in vacuum or exposed to molecular O₂ even under UV illumination, demonstrating that neutral O₂ exhibits minimal reactivity toward the [PbBr₆]⁴⁻ framework. In contrast, oxygen plasma generates highly reactive atomic and ionic oxygen species that induce rapid and spatially heterogeneous photoluminescence quenching. This degradation is attributed to Br⁻ extraction, Br-vacancy formation, and subsequent Pb–O bond generation, which collectively introduce deep trap states and enhance nonradiative recombination. These findings clearly indicate that reactive oxygen species rather than molecular O₂ are the dominant driver of oxygen-induced luminescence degradation, providing mechanistic insight and offering processing guidelines for the reliable integration of perovskite nanomaterials in optoelectronic devices. Full article

Aluminum scandium nitride (Al_1−xSc_xN) is a promising ferroelectric material for non-volatile random-access memory devices and electromechanical sensors. However, adverse effects on polarization from electrical leakage are a significant concern for this material. We observed that the electrical conductivity of Al_1−xSc_xN thin films grown on epitaxial TiN(111) buffered Si(111) follows an Arrhenius-type behavior versus the growth temperature, suggesting that point defect incorporation during growth influences the electronic properties of the film. Photoluminescence intensity shows an inverse correlation with growth temperature, which is consistent with increased non-radiative recombination from point defects. Further characterization using secondary ion mass spectrometry in a focused ion beam/scanning electron microscope shows a correlation between trace Ti concentrations in Al_1−xSc_xN films and the growth temperature, further suggesting that extrinsic dopants or alloying components potentially contribute to the point defect chemistry to influence electrical transport. Investigation of the enthalpy of formation of nitrogen vacancies in Al_1−xSc_xN using density functional theory yields values that are in line with electrical conductivity measurements. Additionally, the dependence of nitrogen-vacancy formation energy on proximity to Sc atoms suggests that variations in the local structure may contribute to the occurrence of point defects, which, in turn, can impact electrical leakage. Furthermore, we have demonstrated ferroelectric behavior through electrical measurements and piezoresponse force microscopy after dc bias poling of films in spite of electrical conductivity spanning several orders of magnitude. Although electrical leakage remains a challenge in Al_1−xSc_xN, the material holds potential due to tunable electrical conductivity as a semiconducting ferroelectric material. Full article

Barium disilicide (BaSi₂) was identified as a promising silicon-based photovoltaic absorber due to its near-optimal bandgap, strong optical absorption, and earth-abundant composition. However, the performance of BaSi₂ thin-film solar cells was severely restricted by structural defects and interfacial instabilities that introduced localized electronic states and facilitated non-radiative recombination. These imperfections degraded carrier lifetime, mobility, and open-circuit voltage. This review systematically examined the formation, energetics, and electronic roles of intrinsic and extrinsic defects in BaSi₂ thin films, and evaluated nanoscale passivation strategies developed to mitigate defect-induced losses. Chemical, dielectric, and interfacial approaches were critically analyzed with emphasis on their underlying mechanisms, limitations, and integration potential. The convergence of in situ characterization, first-principles modeling, and data-driven process optimization was expected to enable predictive defect control and rational interface design, thereby advancing BaSi₂-based photovoltaics toward practical implementation. Full article

Wide-bandgap (WBG) perovskite solar cells (PSCs) are critical for high-efficiency tandem photovoltaic devices, but their practical application is severely limited by phase separation and poor film quality. To address these challenges, this study proposes a dual-additive passivation strategy using potassium thiocyanate (KSCN) and potassium chloride (KCl) to synergistically optimize the crystallinity and defect state of WBG perovskite films. The selection of KSCN/KCl is based on their complementary functionalities: K⁺ ions occupy lattice vacancies to suppress ion migration, Cl⁻ ions promote oriented crystal growth, and SCN⁻ ions passivate surface defects via Lewis acid-base interactions. A series of KSCN/KCl concentrations (relative to Pb) were tested, and the effects of dual additives on film properties and device performance were systematically characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), photoluminescence (PL), space-charge-limited current (SCLC), current-voltage (J-V), and external quantum efficiency (EQE) measurements. Results show that the dual additives significantly enhance film crystallinity (average grain size increased by 27.0% vs. control), reduce surface roughness (from 86.50 nm to 24.06 nm), and passivate defects-suppressing non-radiative recombination and increasing electrical conductivity. For WBG PSCs, the champion device with KSCN (0.5 mol%) + KCl (1 mol%) exhibits a power conversion efficiency (PCE) of 16.85%, representing a 19.4% improvement over the control (14.11%), along with enhanced open-circuit voltage (Voc: +2.8%), short-circuit current density (Jsc: +6.7%), and fill factor (FF: +8.9%). Maximum power point (MPP) tracking confirms superior operational stability under illumination. This dual-inorganic-additive strategy provides a generalizable approach for the rational design of stable, high-efficiency WBG perovskite films. Full article

Minimizing surface defects in perovskite films is crucial for suppressing non-radiative recombination and enhancing device performance. Herein, we propose the use of N-bromosuccinimide (NBS), a small molecule containing Lewis base carbonyl groups (C=O), to improve the quality of RbCsMAFA mixed-cation perovskite films. This surface treatment effectively reduces non-radiative charge-carrier recombination, in particular through the passivation of surface defects related to undercoordinated Pb²⁺ ions and halide vacancies, and significantly accelerates charge extraction from the perovskite into the Spiro-OMeTAD hole transporter. Consequently, NBS-treated PerSCs achieve a power conversion efficiency (PCE) of 18.24%, representing an 11% relative increase over the control device (16.48%). This enhancement is mainly attributed to a V_oc gain of up to 40 mV and modifications in the recombination dynamics. Supporting evidence from impedance spectroscopic analyses further confirms enhanced energy-level alignment and reduced interfacial losses, improved charge transport as well as prolonged charge lifetimes within the devices. This work provides a simple yet effective approach to reduce the non-radiative recombination losses towards more efficient and stable PerSCs. Full article

Perovskite materials have garnered significant attention in both fundamental research and practical applications owing to their exceptional light absorption coefficients, low fabrication costs, and inherent advantages for thin-film and flexible device fabrication. Nevertheless, interface defects within perovskite films induce detrimental non-radiative carrier recombination and pronounced hysteresis effects, which collectively impose substantial limitations on the photovoltaic performance and long-term operational stability of perovskite solar cells (PSCs). Conventional passivation strategies, despite their demonstrated efficacy in mitigating interface defects, often inadvertently introduce secondary defects in originally defect-free regions, thereby restricting the extent of device performance improvement. To overcome this critical limitation, we have developed a precision defect passivation methodology that employs a targeted two-step immersion–cleaning process, achieving selective defect passivation while concomitantly eliminating residual passivating agents. This approach effectively prevents the formation of new defects in unaffected regions of the perovskite films, and the resultant PSC possesses a power conversion efficiency (PCE) of 21.08%, accompanied by a substantial mitigation of hysteresis behavior. Furthermore, unencapsulated devices demonstrate remarkable stability, retaining over 81% of their initial efficiency after 20 days of atmospheric storage under 50% relative humidity, which underscores the effectiveness of our passivation strategy in simultaneously enhancing both device performance and operational stability. Full article

Quasi-two-dimensional (Q2D) perovskite films have garnered significant attention as novel gain media for lasers due to their tunable bandgap, narrow linewidth, and solution processability. Q2D perovskites endowed with intrinsic quantum well structures demonstrate remarkable potential as gain media for cost-effective miniaturized lasers, owing to their superior ambient stability and enhanced photon confinement capabilities. However, the mixed-phase distribution within Q2D films constitutes a critical determinant of their optical properties, exhibiting pronounced sensitivity to specific fabrication protocols and processing parameters, including annealing temperature, duration, antisolvent volume, injection timing, and dosing rate. These factors frequently lead to broad phase distribution in Q2D perovskite films, thereby inducing incomplete exciton energy transfer and multiple emission peaks, while simultaneously making the fabrication processes intricate and reducing reproducibility. Here, we report a novel annealing-free and antisolvent-free method for the preparation of Q2D perovskite films fabricated in ambient atmosphere. By constructing a tailored mixed-solvent vapor atmosphere and systematically investigating its regulatory effects on the nucleation and growth processes of film via in situ photoluminescence spectra, we successfully achieved the fabrication of Q2D perovskite films with large n narrow phase distribution characteristics. Due to the reduced content of small n domains, the incomplete energy transfer from small n to large n phases and the carriers’ accumulation in small n can be greatly suppressed, thereby suppressing the trap-assistant nonradiative recombination and Auger recombination. Ultimately, the Q2D perovskite film showed a single emission peak at 519 nm with the narrow full width at half maximum (FWHM) of 21.5 nm and high photoluminescence quantum yield (PLQY) of 83%. And based on the optimized Q2D film, we achieved an amplified spontaneous emission (ASE) with a low threshold of 29 μJ·cm⁻², which was approximately 60% lower than the 69 μJ·cm⁻² of the control film. Full article

We report the observation of a linear electro-optic (EO) response in CsPbX₃ (X = Cl, Br, I) perovskite nanocrystal (NC) films fabricated via electrophoretic deposition (EPD). Under an alternating electric field, the EPD films exhibit clear linear EO modulation of transmitted light intensity, indicating the formation of an anisotropic medium through field-induced NC alignment. In contrast, spin-coated NC films show no measurable linear EO response, underscoring the critical role of structural anisotropy introduced by EPD. All EPD samples exhibit a decreasing EO response with increasing modulation frequency, consistent with the involvement of slow ion migration dynamics. The halide composition influences EO behavior, with Br/Cl mixed-composition films maintaining the highest EO response at elevated frequencies, and Br-based NCs showing stronger EO signals than their Cl counterparts, while Bi-doped CsPbBr₃ films exhibit quenched photoluminescence yet retain a measurable but weaker EO response, underscoring the trade-off between defect-induced nonradiative recombination and EO activity. These results highlight the potential of EPD-assembled perovskite NCs for reconfigurable EO applications by tailoring composition and microstructure. Full article

Halide perovskite-based memristors are promising neuromorphic devices due to their unique ion migration and interface tunability, yet their conduction mechanisms remain unclear, causing stability and performance issues. Here, we engineer interstitial Ag⁺ ions within a quasi-two-dimensional (quasi-2D) halide perovskite ((C₆H₅C₂H₄NH₃)₂Cs_n−1Pb_nI_3n+1) to enhance device stability and controllability. The introduced Ag⁺ ions occupy organic interlayers, forming thermodynamically stable structures and introducing deep-level energy states without structural distortion, which do not act as non-radiative recombination centers, but instead serve as efficient charge trapping centers that stabilize intermediate resistance states and facilitate controlled filament evolution during resistive switching. This modification also leads to enhanced electron transparency near the Fermi level, contributing to improved charge transport dynamics and device performance. Under external electric fields, these Ag⁺ ions act as mobile ionic species, facilitating controlled filament formation and stable resistive switching. The resulting devices demonstrate exceptional performance, featuring an ultrahigh on/off ratio (∼10⁸) and low operating voltages (∼0.31 V), surpassing existing benchmarks. Our findings highlight the dual role of Ag⁺ ions in structural stabilization and conduction modulation, providing a robust approach for high-performance perovskite memristor engineering. Full article

The GaN-based green miniaturized light-emitting diode (mini-LED) is a key component for the realization of full-color display. Optimized passivation layers can alleviate the trapping of carriers by sidewall defects and are regarded as an effective way to improve the external quantum efficiency (EQE) efficiency of mini-LEDs. Since AlN has a closer lattice match to GaN compared to other heterogeneous passivation materials, we boosted the EQE of GaN-based green flip-chip mini-LEDs through the deposition of a lattice-compatible AlN passivation layer through atomic layer deposition (ALD) and a SiO₂ passivation layer through plasma-enhanced chemical vapor deposition (PECVD). Benefiting from reduced sidewall nonradiative recombination, the EQE of the green flip-chip mini-LED with a composite ALD-AlN/PECVD-SiO₂ passivation layer reached 34.14% at 5 mA, which is 34.6% higher than that of the green flip-chip mini-LED with a single PECVD-SiO₂ passivation layer. The results provide guidance for the realization of high-performance mini-LEDs by selecting lattice-compatible passivation layers. Full article

In recent years, inverted perovskite solar cells (PSCs) have garnered widespread attention due to their high compatibility, excellent stability, and potential for low-temperature manufacturing. However, most of the current research has primarily focused on the surface passivation of perovskite. In contrast, the buried interface significantly influences the crystal growth quality of perovskite, but it is difficult to effectively control, leading to relatively slow research progress. To address the issue of poor interfacial contact between the hole transport-layer nickel oxide (NiOX) and the perovskite, we introduced a conjugated self-assembled monolayer (SAM), 4,4′-[(4-(3,6-dimethoxy-9H-carbazole)triphenylamine)]diphenylacetic acid (XS21), which features triphenylamine dicarboxylate groups. For comparison, we also employed the widely studied phosphonic acid-based SAM, [2-(3,6-dimethoxy-9H-carbazole-9-yl)ethyl] phosphonic acid (MeO-2PACz). A systematic investigation was carried out to evaluate the influence of these SAMs on the performance and stability of inverted PSCs. The results show that both XS21 and MeO-2PACz significantly enhanced the crystallinity of the perovskite layer, reduced defect densities, and suppressed non-radiative recombination. These improvements led to more efficient hole extraction and transport at the buried interface. Consequently, inverted PSCs incorporating XS21 and MeO-2PACz achieved impressive power-conversion efficiencies (PCEs) of 21.43% and 22.43%, respectively, along with marked enhancements in operational stability. Full article

Mn²⁺ doped metal halide that can be grown by a facile solution reaction is a promising low-cost afterglow material. However, the afterglow mechanism is still elusive. Using a facile method to modulate afterglow time is still to be explored. In this work, we reveal that the afterglow of Cs₂Na_0.2Ag_0.8InCl₆:y%Mn can be significantly modulated by Mn²⁺ concentration. We propose that replacing Ag⁺ with Mn²⁺ leads to the appearance of interstitial Ag⁺, which temporally store the photogenerated electrons (${\mathrm{A}\mathrm{g}}^{+}+{\mathrm{e}}^{-}\to \mathrm{A}\mathrm{g}$). After the removal of excitation, the gradual recombination between residual holes and stored electrons [${\mathrm{h}}^{+}+\left({\mathrm{A}\mathrm{g}}^{+}+{\mathrm{e}}^{-}\right)\to \mathrm{h}\mathsf{\nu }+{\mathrm{A}\mathrm{g}}^{+}$] explains the afterglow. However, excessive Mn²⁺ doping at interstitial sites does not bring about more interstitial Ag⁺ but instead introduces nonradiative traps. Therefore, as the Mn²⁺ concentration increases, the afterglow time increases from 350 s to 530 s and then decreases to 230 s, reaching a maximum at y = 40. Thus, a dynamic optical information storage and encryption application is demonstrated based on the modulated afterglow time. Full article

In this study, we investigate the influence of the halogen elements bromine (Br) and chlorine (Cl) on iodine defect properties primarily in FAPbI₃ through first-principles calculations, aiming to understand the effect of high defect densities on the efficiency of organic–inorganic hybrid perovskite cells. The results indicate that Br and Cl interstitials minimally alter the overall band structure of FAPbI₃ but significantly modify the defect energy levels. Br and Cl interstitials, with defect states closer to the valence band and lower formation energies, effectively convert deep-level traps induced by iodine interstitials (I_i) into shallow-level traps. This conversion enhances carrier transport by reducing non-radiative recombination while preserving light absorption efficiency. Excess Br/Cl co-doping in FAPbI₃ synthesis thereby suppresses non-radiative recombination and mitigates the detrimental effects of iodide-related defects. Full article

We report an advanced passivation strategy for perovskite solar cells (PSCs) by introducing core–shell structured perovskite quantum dots (PQDs), composed of methylammonium lead bromide (MAPbBr₃) cores and tetraoctylammonium lead bromide (tetra-OAPbBr₃) shells, during the antisolvent-assisted crystallization step. The epitaxial compatibility between the PQDs and the host perovskite matrix enables effective passivation of grain boundaries and surface defects, thereby suppressing non-radiative recombination and facilitating more efficient charge transport. At an optimal PQD concentration of 15 mg/mL, the modified PSCs demonstrated a remarkable increase in power conversion efficiency (PCE) from 19.2% to 22.85%. This enhancement is accompanied by improved device metrics, including a rise in open-circuit voltage (Voc) from 1.120 V to 1.137 V, short-circuit current density (Jsc) from 24.5 mA/cm² to 26.1 mA/cm², and fill factor (FF) from 70.1% to 77%. Spectral response analysis via incident photon-to-current efficiency (IPCE) revealed enhanced photoresponse in the 400–750 nm wavelength range. Additionally, long-term stability assessments showed that PQD-passivated devices retained more than 92% of their initial PCE after 900 h under ambient conditions, outperforming control devices which retained ~80%. These findings underscore the potential of in situ integrated PQDs as a scalable and effective passivation strategy for next-generation high-efficiency and stable perovskite photovoltaics. Full article