Photodetectors Based on MASnI3/MoS2 Hybrid-Dimensional Heterojunction Transistors: Breaking the Responsivity-Speed Trade-Off.

Hybrid-dimensional heterojunction transistor (HDHT) photodetectors (PDs) have achieved high responsivities but unfortunately are still with unacceptably slow response speeds. Here, we propose a MASnI3/MoS2 HDHT PD, which exhibits the possibility to obtain high responsivity and fast response simultaneously. By exploring the detailed photoelectric responses utilizing a precise optoelectronic coupling simulation, the electrical performance of the device is optimally manipulated and the underlying physical mechanisms are carefully clarified. Particularly, the influence and modulation characteristics of the trap effects on the carrier dynamics of the PDs are investigated. We find that the localized trap effect in perovskite, especially at its top surface, is primarily responsible for the high responsivity and long response time; moreover, it is normally hard to break such a responsivity-speed trade-off due to the inherent limitation of the trap effect. By synergistically coupling the photogating effect, trap effect, and gate regulation, we indicate that it is possible to achieve an enhancement of the responsivity-bandwidth product by about 3 orders of magnitude. This study facilitates a fine modulation of the responsivity-speed relationship of hybrid-dimensional PDs, enabling breaking the traditional responsivity-speed trade-off of many PDs.

Unveiling Energy Conversion Mechanisms and Regulation Strategies in Perovskite Solar Cells.

Despite recent revolutionary advancements in photovoltaic (PV) technology, further improving cell efficiencies toward their Shockley-Queisser (SQ) limits remains challenging due to inherent optical, electrical, and thermal losses. Currently, most research focuses on improving optical and electrical performance through maximizing spectral utilization and suppressing carrier recombination losses, while there is a serious lack of effective opto-electro-thermal coupled management, which, however, is crucial for further improving PV performance and the practical application of PV devices. In this article, the energy conversion and loss processes of a PV device (with a specific focus on perovskite solar cells) are detailed under both steady-state and transient processes through rigorous opto-electro-thermal coupling simulation. By innovatively coupling multi-physical behaviors of photon management, carrier/ion transport, and thermodynamics, it meticulously quantifies and analyzes energy losses across optical, electrical, and thermal domains, identifies heat components amenable to regulation, and proposes specific regulatory means, evaluates their impact on device efficiency and operating temperature, offering valuable insights to advance PV technology for practical applications.

Self-powered MSM solar-blind AlGaN photodetector realized by in-plane polarization modulation.

Solid-state self-powered UV detection is strongly required in various application fields to enable long-term operation. However, this requirement is incompatible with conventionally used metal-semiconductor-metal (MSM) UV photodetectors (PDs) due to the symmetric design of Schottky contacts. In this work, a self-powered MSM solar-blind UV-PD was realized using a lateral pn junction architecture. A large built-in electric field was obtained in the MSM-type UV-PD without impurity doping, leading to efficiency carrier separation and enhanced photoresponsivity at zero external bias. The solar-blind UV-PD exhibits a cutoff wavelength of 280 nm, a photo/dark current ratio of over 105, and a responsivity of 425.13 mA/W at -10 V. The mechanism of self-powered UV photodetection was further investigated by TCAD simulation of the internal electric field and carrier distributions.

Novel polysilicon in resisting thermal-evaporation Al-electrode damage and its application in back-junction passivated contact p-type solar cells.

In preparing tunnel oxygen passivation contact (TOPCon) solar cells, the metallization process often causes damage to passivation performance. Aiming to solve the issue, we investigated the advantages of the novel polysilicon, i.e. the carbon (C) or nitrogen (N) doped polysilicon, in resisting metallization damage. Our study reveals that C- or N-doped polysilicon does mitigate the passivation damage caused by the physical-vapor deposition metallization processes, i.e. the decrease in implied open-circuit voltage (iVoc) and the increase in recombination current (J0) are both suppressed. For the novel polysilicon samples suffered metallization, the decrease ofiVocwas only ∼-1 mV, and the increase ofJ0< 1 fA cm-2; in contrast, the decrease ofiVocof the standard polysilicon samples was -7 mV, and the increase ofJ0was ∼6 fA cm-2. In addition, we also explored the difference between the finger-metal and the full-metal metallization, showing that the finger-metal has less passivation damage due to the smaller contact area. However, the free energy loss analysis indicates that the advantage of the novel polysilicon in resisting metallization damage is overshadowed by the disadvantage of the higher contact resistivity when finger-metal electrodes are used. Numerical simulations prove that the efficiency of the solar cell with novel polysilicon still shows >0.2% absolute efficiency higher than that with the standard polysilicon, reaching 26% when full-metal electrodes by thermal evaporation.

Regionalizing Nitrogen Doping of Polysilicon Films Enabling High-Efficiency Tunnel Oxide Passivating Contact Silicon Solar Cells.

Tunnel oxide passivating contact (TOPCon) solar cells (SCs) as one of the most competitive crystalline silicon (c-Si) technologies for the TW-scaled photovoltaic (PV) market require higher passivation performance to further improve their device efficiencies. Here, the successful construction of a double-layered polycrystalline silicon (poly-Si) TOPCon structure is reported using an in situ nitrogen (N)-doped poly-Si covered by a normal poly-Si, which achieves excellent passivation and contact properties simultaneously. The new design exhibits the highest implied open-circuit voltage of 755 mV and the lowest single-sided recombination current density (J0 ) of ≈0.7 fA cm⁻2 for a TOPCon structure and a low contact resistivity of less than 5 mΩ·cm2 , resulting in a high selectivity factor of ≈16. The mechanisms of passivation improvement are disclosed, which suggest that the introduction of N atoms into poly-Si restrains H overflow by forming stronger Si-N and N-H bonds, reduces interfacial defects, and induces favorable energy bending. Proof-of-concept TOPCon SCs with such a design receive a remarkable certified efficiency of 25.53%.

Visualizing Interfacial Energy Offset and Defects in Efficient 2D/3D Heterojunction Perovskite Solar Cells and Modules.

Currently, the full potential of perovskite solar cells (PSCs) is limited by chargecarrier recombination owing to imperfect passivation methods. Here, the recombination loss mechanisms owing to the interfacial energy offset and defects are quantified. The results show that a favorable energy offset can reduce minority carriers and suppress interfacial recombination losses more effectively than chemical passivation. To obtain high-efficiency PSCs, 2D perovskites are promising candidates, which offer powerful field effects and require only modest chemical passivation at the interface. The enhanced passivation and charge-carrier extraction offered by the 2D/3D heterojunction PSCs has boosted their power conversion efficiency to 25.32% (certified 25.04%) for small-size devices and to 21.48% for a large-area module (with a designated area of 29.0 cm2 ). Ion migration is also suppressed by the 2D/3D heterojunction, such that the unencapsulated small-size devices maintain 90% of their initial efficiency after 2000 h of continuous operation at the maximum power point.

Extending the π-Conjugated System in Spiro-Type Hole Transport Material Enhances the Efficiency and Stability of Perovskite Solar Modules.

Hole transport materials (HTMs) are a key component of perovskite solar cells (PSCs). The small molecular 2,2',7,7'-tetrakis(N,N-di-p-methoxyphenyl)-amine-9,9'-spirobifluorene (spiro-OMeTAD, termed "Spiro") is the most successful HTM used in PSCs, but its versatility is imperfect. To improve its performance, we developed a novel spiro-type HTM (termed "DP") by substituting four anisole units on Spiro with 4-methoxybiphenyl moieties. By extending the π-conjugation of Spiro in this way, the HOMO level of the HTM matches well with the perovskite valence band, enhancing hole mobility and increasing the glass transition temperature. DP-based PSC achieves high power conversion efficiencies (PCEs) of 25.24 % for small-area (0.06 cm2 ) devices and 21.86 % for modules (designated area of 27.56 cm2 ), along with the certified efficiency of 21.78 % on a designated area of 27.86 cm2 . The encapsulated DP-based devices maintain 95.1 % of the initial performance under ISOS-L-1 conditions after 2560 hours and 87 % at the ISOS-L-3 conditions over 600 hours.

Surface Reconstruction for Efficient and Stable Monolithic Perovskite/Silicon Tandem Solar Cells with Greatly Suppressed Residual Strain.

Despite the swift rise in power conversion efficiency (PCE) to more than 32%, the instability of perovskite/silicon tandem solar cells is still one of the key obstacles to practical application and is closely related to the residual strain of perovskite films. Herein, a simple surface reconstruction strategy is developed to achieve a global incorporation of butylammonium cations at both surface and bulk grain boundaries by post-treating perovskite films with a mixture of N,N-dimethylformamide and n-butylammonium iodide in isopropanol solvent, enabling strain-free perovskite films with simultaneously reduced defect density, suppressed ion migration, and improved energy level alignment. As a result, the corresponding single-junction perovskite solar cells yield a champion PCE of 21.8%, while maintaining 100% and 81% of their initial PCEs without encapsulation after storage for over 2500 h in N2 and 1800 h in air, respectively. Remarkably, a certified stabilized PCE of 29.0% for the monolithic perovskite/silicon tandems based on tunnel oxide passivated contacts is further demonstrated. The unencapsulated tandem device retains 86.6% of its initial performance after 306 h at maximum power point (MPP) tracking under continuous xenon-lamp illumination without filtering ultraviolet light (in air, 20-35 °C, 25-75%RH, most often ≈60%RH).

Long-chain anionic surfactants enabling stable perovskite/silicon tandems with greatly suppressed stress corrosion.

Despite the remarkable rise in the efficiency of perovskite-based solar cells, the stress-induced intrinsic instability of perovskite active layers is widely identified as a critical hurdle for upcoming commercialization. Herein, a long-alkyl-chain anionic surfactant additive is introduced to chemically ameliorate the perovskite crystallization kinetics via surface segregation and micellization, and physically construct a glue-like scaffold to eliminate the residual stresses. As a result, benefiting from the reduced defects, suppressed ion migration and improved energy level alignment, the corresponding unencapsulated perovskite single-junction and perovskite/silicon tandem devices exhibit impressive operational stability with 85.7% and 93.6% of their performance after 3000 h and 450 h at maximum power point tracking under continuous light illumination, providing one of the best stabilities to date under similar test conditions, respectively.

De Novo Studies of Working Mechanisms for Self-Driven Narrowband Perovskite Photodetectors.

Self-driven narrowband perovskite photodetectors have recently attracted significant attention due to their simple preparation, high performance, and amenability for system integration. However, the origin of narrowband photoresponse and the related regulation mechanisms still remains elusive. To address these issues, we herein perform a systematic investigation by formulating an analytic model in conjunction with finite element simulation. The optical and electrical simulations have resulted in design principles for perovskite narrowband photodetectors in terms of the dependence of external quantum efficiency (EQE) on perovskite layer thickness, doping concentration, and band gap as well as trap state concentration. Careful investigations on the profiles of electric field, current, and optical absorption reveal the dependence of narrowband EQE on the direction of incident light and perovskite doping types: only p-type perovskite can yield the narrowband photoresponse for illumination from the hole transport layer (HTL) side. The simulation results demonstrated in this study shed new light on the mechanism of perovskite-based narrowband photodetectors and provide valuable guidance for their design.

Reference role of middle turbinate axilla in lacrimal sac localization assisted by computed tomographic dacryocystography-reference value of middle turbinate in locating lacrimal sac.

BACKGROUND: The middle turbinate axilla (MTA) has always been used as a stable anatomic landmark for endoscopic surgeons to locate the lacrimal sac on the lateral nasal wall. Yet, little is known about whether the lacrimal sac size will affect the positioning effect of MTA on lacrimal sac. The aim of this study was to investigate the regularity of lacrimal sac size and lacrimal sac localization through the reference position of the MTA on computed tomographic dacryocystography (CT-DCG) images. METHODS: A series of 192 endoscopic dacryocystorhinostomy (DCR) surgeries were performed. All the patients had been diagnosed as unilateral nasolacrimal duct obstruction and received CT-DCG examinations. According to the maximum transverse diameter of the lacrimal sac on CT-DCG, the patients were classified into three groups. Measurements were taken on CT-DCG parasagittal images. RESULTS: The average distance from the sac superior fundus (SSF) to the MTA was 7.52 mm ± 3.23 mm, and it increased with the increase of the maximum transverse diameter of the sac among groups (p < 0.01). The average distance from the common canaliculus (CC) to the MTA was 3.95 mm ± 2.49 mm. No significant difference was observed among the groups (p = 0.11). The average distance from the CC to the SSF was 3.41 mm ± 1.31 mm, and it increased with the increase of the sac transverse diameter among groups (p < 0.01). CONCLUSIONS: The lacrimal sac can be accurately located on the lateral nasal wall by the reference position of the MTA on CT-DCG images. The distance of the SSF to the MTA and the SSF to the CC is related to the lacrimal sac size. The relative position of the CC to the MTA is relatively stable on CT-DCG images, which make it possible to locate the lacrimal sac of different sizes and the corresponding nasal mucosa incision design in endoscopic DCR.

50-µm thick flexible dopant-free interdigitated-back-contact silicon heterojunction solar cells with front MoOx coatings for efficient antireflection and passivation.

We demonstrate experimentally a flexible crystalline silicon (c-Si) solar cell (SC) based on dopant-free interdigitated back contacts (IBCs) with thickness of merely 50 µm for, to the best of our knowledge, the first time. A MoOx thin film is proposed to cover the front surface and the power conversion efficiency (PCE) is boosted to over triple that of the uncoated SC. Compared with the four-time thicker SC, our thin SC is still over 77% efficient. Systematic studies show the front MoOx film functions for both antireflection and passivation, contributing to the excellent performance. A double-interlayer (instead of a previously-reported single interlayer) is identified at the MoOx/c-Si interface, leading to efficient chemical passivation. Meanwhile, due to the large workfunction difference, underneath the interface a strong built-in electric field is generated, which intensifies the electric field over the entire c-Si active layer, especially in the 50-µm thick layer. Photocarriers are expelled quickly to the back contacts with less recombined and more extracted. Besides, our thin IBC SC is highly flexible. When bent to a radius of 6 mm, its PCE is still 76.6% of that of the unbent cell. Fabricated with low-temperature and doping-free processes, our thin SCs are promising as cost-effective, light-weight and flexible power sources.

Single-crystalline TiO2 nanoparticles for stable and efficient perovskite modules.

Despite the remarkable progress in power conversion efficiency of perovskite solar cells, going from individual small-size devices into large-area modules while preserving their commercial competitiveness compared with other thin-film solar cells remains a challenge. Major obstacles include reduction of both the resistive losses and intrinsic defects in the electron transport layers and the reliable fabrication of high-quality large-area perovskite films. Here we report a facile solvothermal method to synthesize single-crystalline TiO2 rhombohedral nanoparticles with exposed (001) facets. Owing to their low lattice mismatch and high affinity with the perovskite absorber, their high electron mobility and their lower density of defects, single-crystalline TiO2 nanoparticle-based small-size devices achieve an efficiency of 24.05% and a fill factor of 84.7%. The devices maintain about 90% of their initial performance after continuous operation for 1,400 h. We have fabricated large-area modules and obtained a certified efficiency of 22.72% with an active area of nearly 24 cm2, which represents the highest-efficiency modules with the lowest loss in efficiency when scaling up.

Eye Avoidance of Threatening Facial Expressions in Parents of Children with ASD.

OBJECTIVE: Previous research found that autism spectrum disorder (ASD) was characterized by eye avoidance of threatening facial expressions. However, it still remains unclear as to whether these abnormalities are present in parents of children with ASD. Our study aimed to investigate the gaze patterns of parents of children with ASD in the threatening facial expressions. METHODS: Thirty-four parents of children with ASD and 35 parents of typically developing (TD) children participated in our study. We investigated the total fixation time of participants when they viewed different facial expression (eg, happy, fearful, angry, sad) videos and examined changes in the fixation duration over time. RESULTS: We observed the following: a) the total fixation time of the parents of children with ASD on the eyes of fearful faces was significantly shorter than that of the normal group, and the difference lasted for five seconds (four to six seconds, eight to nine seconds) throughout the process; and b) The parents of children with ASD avoided the eyes of angry expression faces at around five seconds after the stimulus onset. CONCLUSION: We concluded that parents of children with ASD tended to avoid the eyes of threatening expression faces while viewing the dynamic emotions video.

Light-Promoted Electrostatic Adsorption of High-Density Lewis Base Monolayers as Passivating Electron-Selective Contacts.

Achieving efficient passivating carrier-selective contacts (PCSCs) plays a critical role in high-performance photovoltaic devices. However, it is still challenging to achieve both an efficient carrier selectivity and high-level passivation in a sole interlayer due to the thickness dependence of contact resistivity and passivation quality. Herein, a light-promoted adsorption method is demonstrated to establish high-density Lewis base polyethylenimine (PEI) monolayers as promising PCSCs. The promoted adsorption is attributed to the enhanced electrostatic interaction between PEI and semiconductor induced by the photo-generated carriers. The derived angstrom-scale PEI monolayer is demonstrated to simultaneously provide a low-resistance electrical contact for electrons, a high-level field-effect passivation to semiconductor surface and an enhanced interfacial dipole formation at contact interface. By implementing this light-promoted adsorbed PEI as a single-layered PCSC for n-type silicon solar cell, an efficiency of 19.5% with an open-circuit voltage of 0.641 V and a high fill factor of 80.7% is achieved, which is one of the best results for devices with solution-processed electron-selective contacts. This work not only demonstrates a generic method to develop efficient PCSCs for solar cells but also provides a convenient strategy for the deposition of highly uniform, dense, and ultra-thin coatings for diverse applications.

Design and simulation of perovskite solar cells with Gaussian structured gradient-index optics.

To unlock the full potential of the perovskite solar cell (PSC) photocurrent density and power conversion efficiency, the topic of optical management and design optimization is of absolute importance. Here, we propose a gradient-index optical design of the PSC based on a Gaussian-type front-side glass structure. Numerical simulations clarify a broadband light-harvesting response of the new design, showing that a maximal photocurrent density of 23.35 mA/cm2 may be expected, which is an increase by 1.21 mA/cm2 compared with that of the traditional flat-glass counterpart (22.14 mA/cm2). Comprehensive analysis of the electric field distributions elucidates the light-trapping mechanism. Furthermore, PSCs having the Gaussian index profile display superior optical properties and performance compared to those of the uniform index counterpart under varying conditions of perovskite layer thicknesses and incident angles. The simulation results in this study provide an effective design scheme to promote optical absorption in PSCs.

Omnidirectional whispering-gallery-mode lasing in GaN microdisk obtained by selective area growth on sapphire substrate.

The optical properties of hexagonal GaN microdisk arrays grown on sapphire substrates by selective area growth (SAG) technique were investigated both experimentally and theoretically. Whispering-gallery-mode (WGM) lasing is observed from various directions of the GaN pyramids collected at room temperature, with the dominant lasing mode being Transverse-Electric (TE) polarized. A relaxation of compressive strain in the lateral overgrown region of the GaN microdisk is illustrated by photoluminescence (PL) mapping and Raman spectroscopy. A strong correlation between the crystalline quality and lasing behavior of the GaN microdisks was also demonstrated.

Performance enhancement of ultraviolet light emitting diode incorporating Al nanohole arrays.

Enhanced photoluminescence and improved internal quantum efficiency were demonstrated for ultraviolet light emitting diodes (UV-LEDs) with Al nanohole arrays deposited on the top surface. The effects of the thickness and periodicity of the plasmonic structures on the optical properties of UV-LEDs were studied, and an optimized nanohole array parameter was illustrated. Classical electrodynamic simulations showed that the radiated power is mostly concentrated along the edge of the Al nanohole arrays. Even though no obvious dip was observed in the transmission spectra associated with localized surface plasmon resonance, significant improvements in radiatiative recombination and light extraction efficiency were demonstrated, indicating the influence of Al nanohole arrays on the light emission control of UV-LEDs. It is anticipated that the enhanced luminescence can be obtained for various emitting wavelengths by directly adjusting the periodicity and morphology of the Al nanohole arrays and this new technology can alleviate crystal quality requirements of III-nitride thin films in the development of high efficiency UV optoelectronic devices.

Heterojunction Hybrid Solar Cells by Formation of Conformal Contacts between PEDOT:PSS and Periodic Silicon Nanopyramid Arrays.

Surface nanotexturing with excellent light-trapping property is expected to significantly increase the conversion efficiency of solar cells. However, limited by the serious surface recombination arising from the greatly enlarged surface area, the silicon (Si) nanotexturing-based solar cells cannot yet achieve satisfactory high efficiency, which is more prominent in organic/Si hybrid solar cells (HSCs) where a uniform polymer layer can rarely be conformably coated on nanotextured substrate. Here, the HSCs featuring advanced surface texture of periodic upright nanopyramid (UNP) arrays and hole-conductive conjugated polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), are investigated. The tetramethylammonium hydroxide etching is used to smooth the surface morphologies of the Si-UNPs, leading to reduced surface defect states. The uniform Si-UNPs together with silane chemical-incorporated PEDOT:PSS solution enable the simultaneous realization of excellent broadband light absorption as well as enhanced electrical contact between the textured Si and the conducting polymer. The resulting PEDOT:PSS/Si HSCs textured with UNP arrays show a promising power conversion efficiency of 13.8%, significantly higher than 12.1% of the cells based on the-state-of-the-art surface texture with random pyramids. These results provide a viable route toward shape-controlled nanotexturing-based high-performance organic/Si HSCs.

Dopant-Free and Carrier-Selective Heterocontacts for Silicon Solar Cells: Recent Advances and Perspectives.

By combining the most successful heterojunctions (HJ) with interdigitated back contacts, crystalline silicon (c-Si) solar cells (SCs) have recently demonstrated a record efficiency of 26.6%. However, such SCs still introduce optical/electrical losses and technological issues due to parasitic absorption/Auger recombination inherent to the doped films and the complex process of integrating discrete p+- and n+-HJ contacts. These issues have motivated the search for alternative new functional materials and simplified deposition technologies, whereby carrier-selective contacts (CSCs) can be formed directly with c-Si substrates, and thereafter form IBC cells, via a dopant-free method. Screening and modifying CSC materials in a wider context is beneficial for building dopant-free HJ contacts with better performance, shedding new light on the relatively mature Si photovoltaic field. In this review, a significant number of achievements in two representative dopant-free hole-selective CSCs, i.e., poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate)/Si and transition metal oxides/Si, have been systemically presented and surveyed. The focus herein is on the latest advances in hole-selective materials modification, interfacial passivation, contact resistivity, light-trapping structure and device architecture design, etc. By analyzing the structure-property relationships of hole-selective materials and assessing their electrical transport properties, promising functional materials as well as important design concepts for such CSCs toward high-performance SCs have been highlighted.