Showing papers by "Yuan Gao published in 2019"

Monolithic all-perovskite tandem solar cells with 24.8% efficiency exploiting comproportionation to suppress Sn( ii ) oxidation in precursor ink

Abstract: Combining wide-bandgap and narrow-bandgap perovskites to construct monolithic all-perovskite tandem solar cells offers avenues for continued increases in photovoltaic (PV) power conversion efficiencies (PCEs). However, actual efficiencies today are diminished by the subpar performance of narrow-bandgap subcells. Here we report a strategy to reduce Sn vacancies in mixed Pb–Sn narrow-bandgap perovskites that use metallic tin to reduce the Sn4+ (an oxidation product of Sn2+) to Sn2+ via a comproportionation reaction. We increase, thereby, the charge-carrier diffusion length in narrow-bandgap perovskites to 3 μm for the best materials. We obtain a PCE of 21.1% for 1.22-eV narrow-bandgap solar cells. We fabricate monolithic all-perovskite tandem cells with certified PCEs of 24.8% for small-area devices (0.049 cm2) and of 22.1% for large-area devices (1.05 cm2). The tandem cells retain 90% of their performance following 463 h of operation at the maximum power point under full 1-sun illumination. Improvements in the efficiency and stability of low-bandgap perovskite solar cells are key to enabling all-perovskite solar cells. Here, Lin et al. use metallic tin to prevent oxidation in such low-gap perovskite and demonstrate 24.8%-efficient tandems that are stable for over 400 h under operating conditions.

Photo-oxidative degradation of methylammonium lead iodide perovskite: mechanism and protection

Abstract: Although the power conversion efficiency of perovskite solar cells has exceeded 23%, the poor ambient stability of organic–inorganic halide perovskites poses a challenge for their commercialization. Comprehensive understanding of the underlying degradation mechanisms is a crucial step to seek approaches that can effectively suppress the degradation of perovskites. Herein, on the basis of extensive first-principles calculations, a three-step photo-oxidative degradation mechanism of MAPbI3 at the atomic level is revealed. We find that, in a dry ambient environment, the photo-generated superoxide anions (O2−) first lead to fast surface oxidation. However, further oxidation of the perovskite interior is hindered by the solid oxidation product. The fresh water produced in surface oxidation leads to the hydration of the inner perovskite and eventual breakage of the MAPbI3 lattice. We devise a practical strategy for protecting MAPbI3 from photo-induced decomposition by anchoring hydrophobic 2-(4-fluorophenyl)propan-2-amine on the surface of MAPbI3. The surface modification significantly retards the photo-induced decomposition.

Giant Alloyed Hot Injection Shells Enable Ultralow Optical Gain Threshold in Colloidal Quantum Wells.

Abstract: As an attractive materials system for high-performance optoelectronics, colloidal nanoplatelets (NPLs) benefit from atomic-level precision in thickness, minimizing emission inhomogeneous broadening...

Dual Functional Molecular Imprinted Polymer-Modified Organometal Lead Halide Perovskite: Synthesis and Application for Photoelectrochemical Sensing of Salicylic Acid

Abstract: This work reports the synthesis of dual functional molecularly imprinted polymer (MIP)-modified organometal lead halide perovskite (CH3NH3PbI3) and its application for photoelectrochemical (PEC) bioanalysis of salicylic acid (SA). Specifically, the CH3NH3PbI3 was encapsulated into the MIPs via a simple thermal polymerization process on the indium tin oxide (ITO) glass, and the as-obtained MIPs/CH3NH3PbI3/ITO electrode was characterized by various techniques, which revealed that the MIPs could not only stabilize CH3NH3PbI3 but also improve the electron-hole separation efficiency of CH3NH3PbI3 under light illumination. In the detection of model analyte SA, the PEC sensor, with numerous amounts of recognition sites to SA, exhibited desirable performance in terms of good sensitivity, selectivity, stability, and feasibility for real sample analysis. This work not only featured the use of MIPs/CH3NH3PbI3 for PEC detection of SA but also provided a new horizon for the design and implementation of functional polymers/perovskite materials in the field of PEC sensors and biosensors.

A Rectifier-Less AC–DC Interface Circuit for Ambient Energy Harvesting From Low-Voltage Piezoelectric Transducer Array

Abstract: This paper presents a rectifier-less ac–dc energy harvesting circuit capable of harvesting energy from multiple low-voltage piezoelectric transducers (PETs). Synchronous electric charge extraction technique, with bidirectional switches, is adopted to achieve rectifier-less ac–dc direct conversion. The inductor is engaged only during the voltage peak of the PET output for a short period of time and therefore, a single inductor can be shared by multiple transducers. A split-capacitor charging topology is employed to harvest both positive and negative half-cycle energies, without the use of an input rectifier. In addition, a self-startup function is incorporated to kick-start the system from low input voltages. A prototype has been implemented with off-the-shelf components. Energy harvesting from three PET energy sources with different resonance frequencies is demonstrated. A peak overall power conversion efficiency of 79% is achieved with a system self-startup voltage of 650 mV.

Electro-Optic Modulation in Hybrid Metal Halide Perovskites

Abstract: Rapid and efficient conversion of electrical signals to optical signals is needed in telecommunications and data network interconnection. The linear electro-optic (EO) effect in noncentrosymmetric materials offers a pathway to such conversion. Conventional inorganic EO materials make on-chip integration challenging, while organic nonlinear molecules suffer from thermodynamic molecular disordering that decreases the EO coefficient of the material. It has been posited that hybrid metal halide perovskites could potentially combine the advantages of inorganic materials (stable crystal orientation) with those of organic materials (solution processing). Here, layered metal halide perovskites are reported and investigated for in-plane birefringence and linear electro-optic response. Phenylmethylammonium lead chloride (PMA2 PbCl4 ) crystals are grown that exhibit a noncentrosymmetric space group. Birefringence measurements and Raman spectroscopy confirm optical and structural anisotropy in the material. By applying an electric field on the crystal surface, the linear EO effect in PMA2 PbCl4 is reported and its EO coefficient is determined to be 1.40 pm V-1 . This is the first demonstration of this effect in hybrid metal halide perovskites, materials that feature both highly ordered crystalline structures and solution processability. The in-plane birefringence and electro-optic response reveal that layered perovskite crystals could be further explored for potential applications in polarizing optics and EO modulation.

A Sub- ${\mu}$ W/Ch Analog Front-End for $\Delta $ -Neural Recording With Spike-Driven Data Compression

Abstract: We present a fully implantable neural recording IC with a spike-driven data compression scheme to improve the power efficiency and preserve crucial data for monitoring brain activities. A difference between two consecutive neural signals, $\Delta $ -neural signal, is sampled in each channel to reduce the full dynamic range and the required resolution of an analog-to-digital converter (ADC), enabling the whole analog chain to be operated at a 0.5-V supply. A set of multiple $\Delta $ -signals are stored in analog memory to extract the magnitude and frequency features of the incoming neural signals, which are utilized to discriminate spikes in these signals instantaneously after the acquisition in the analog domain. The energy- and area-efficient successive approximation ADC is implemented and only converts detected spikes, decreasing the power dissipation and the amount of neural data. A prototype 16-channel neural interface IC was fabricated using a 0.18-μm CMOS process, and each component in the analog front-end was fully characterized. We successfully demonstrated precise spike detection through both in vitro and in vivo acquisition of the neural signal. The prototype chip consumed 0.88 μW/channel at a 0.5-V supply for the recording and compressed about 89% of neural data, saving the power consumption and bandwidth in the system.

Fast electrochemical deposition of CuO/Cu2O heterojunction photoelectrode: Preparation and application for rapid cathodic photoelectrochemical detection of L-cysteine

Abstract: Cathodic photoelectrochemical (PEC) bioanalysis has been drawing more attention in recent years due to the advantages of excellent anti-interference capability. l -cysteine (Cys) is an essential sulfur-containing amino acid and has been intensively addressed as targets in previous anodic PEC bioanalysis. Herein a novel and simple cathodic PEC l -cysteine (Cys) sensor is reported, on the basis of facile electrochemical fabrication of CuO/Cu2O heterojunction photocathode and the selective interaction between the copper and Cys via the formation of Cu S bond. The as-prepared sensor exhibited excellent biosensing performance in terms of high sensitivity, selectivity and stability. In such a sensor, the binding-induced decrease of cathodic photocurrent can be related to target concentration from 0 and 1.5 μM. This cathodic PEC Cys sensor exempted the use of expensive equipment and required no laborious sensor development procedures. We hope it can inspire more interest for further development of simple and practical PEC sensor toward important biomolecules.

Single ultra-high-definition spatial light modulator enabling highly efficient generation of fully structured vector beams.

Abstract: Ultra-high-definition (UHD) spatial light modulators (SLMs) enhance the degree of freedom in the versatile engineering of optical field. Among efforts to explore the capability of SLMs, enhancing the efficiency of light utilization is an everlasting quest to find SLM-based applications. We propose a new method to efficiently generate arbitrary vector beams with a phase-only UHD-SLM. By enabling the UHD-SLM with a rectangle window to work in an in-line and split-screen manner with the help of a polarizing beam splitter, the total conversion efficiency as high as 49% of light beams is realized. Several complex beams, including cylindrical vector beams and higher-order Poincare sphere beams, are experimentally demonstrated. Our method can facilitate application of SLM in optical field manipulation.

Tunable polarization singularity array enabled using superposition of vector curvilinear beams

Abstract: In this paper, we present an approach for creating a polarization singularity array (PSA) along a curvilinear structure by exploring a scheme of coaxially superposing pre-designed component vector beams. Each component vector beam independently and azimuthally modulates inhomogeneous polarization distribution based on a combination of holographic beam shaping techniques and vector beam generation schemes such that the polarization singularity lattice arranged in a tunable curvilinear structure and locations appear after the superposition of component vector beams. The proposed PSA is proven optically in the vector beam generator system, which is based on a multiplex computer-generated hologram.

A 1.6MHz Swing-Boosted Relaxation Oscillator with ±0.15%/V 23.4ppm/°C Frequency Inaccuracy using Voltage-to-Delay Feedback

Abstract: This paper presents a relaxation oscillator for on-chip clock reference or sensor interface application. To improve the frequency stability over temperature and supply variations, a voltage-to-delay feedback is proposed to compensate the circuit delay variation. In addition, a switch-capacitor swing boosting (SCSB) circuit is proposed to enhance the output swing for phase noise reduction. Implemented in 0.18-μm CMOS process, the proposed oscillator shows a 1.6MHz output frequency, with low frequency inaccuracy of 23.4ppm/°C across 0°C–90°C and ±0.15%/V over 1.2V–1.52V. The measured phase noise is −118.6dBc/Hz at 100kHz offset, corresponding to 156dBc/Hz FOM. The oscillator consumes 51.4μW under 1.3V supply voltage.

Plasmon-exciton systems with high quantum yield using deterministic aluminium nanostructures with rotational symmetries.

Abstract: The abundance and corrosion-resistant properties of aluminium, coupled with its compatibility to silicon processing make aluminium an excellent plasmonic material for light–matter interaction in the ultraviolet-visible spectrum. We investigate the interplay of the excitation and emission enhancements of quantum dots coupled with ultra-small aluminium nanoantennae with varying rotational symmetries, where emission enhancements of ∼8 and ∼6 times have been directly measured for gammadion and star-shaped structures. We observed spontaneous emission modification in the Al antenna with a C6 symmetry and deduce a Purcell factor in the range of 68.01 89% in the single antenna and near-unity quantum yield at the plasmonic hotspots. This finding brings us a step closer towards the realization of circularly polarized nanoemitters.

A 13.56 MHz Wireless Power Transfer System with Bidirectional Data Link and Closed-loop Power Control for Implantable Neuromuscular Stimulator

Abstract: This paper presents a 13.56 MHz wireless power transfer (WPT) system for fully implantable neuromuscular stimulator. Bidirectional wireless data link and closed-loop power control functions are incorporated into the WPT system for stable power delivery to the implant. The external power transmitter (PTX) module includes a DC-DC converter and a Class-E power amplifier (PA) for tunable high efficiency power transmission. The forward link command is modulated on the carrier by amplitude-shift keying (ASK) modulation. The implantable power receiver (PRX) module receives power and data simultaneously from the coupling inductors. PTX and PRX are implemented with discrete components and integrated circuit, respectively. Measurement results showed over 90% Class-E PA efficiency and 42% PRX power conversion efficiency.

A 0.034% Charge-Imbalanced Neural Stimulation Front-End (SFE) IC With on-Chip Voltage Compliance Monitoring Circuit and Analysis on Resting Potential by Utilizing the SFE IC

Abstract: The proposed SFE IC adopts an eight-channel H-bridge structure with an integrated voltage compliance monitoring circuit. It has stimulation current ranged from 0.78mA to 6.2mA selected by 3b control and the stimulation current level can be controlled with 7b resolution within a selected current range. The current range can be expanded by using a high current option ranged from 2.71mA to 21.7mA under 3b control. The worst DNL and INL of the stimulation current source are 0.32 LSB and 0.3 LSB, respectively, from all the current ranges. The average mismatch between the cathodic and anodic current pulses in a biphasic stimulus is measured as 0.034% without using charge balancing techniques. The voltage compliance monitoring circuit is based on triode detection of a sensing MOSFET and it shows the detection accuracy of 45mV from its measurement results. The maximum steady-state voltage across the electrodes/ solution interface (resting potential) is also rigorously analyzed and verified through bench-top and saline experiments by utilizing the proposed stimulator. The SFE IC was fabricated in $0.18~\mu \text{m}$ 24 V CMOS process.

A 100-mV pp Input Range 10-kHz BW VCO-based CT-DSM Neuro-Recording IC in 40-nm CMOS

Abstract: This paper presents a time-domain continuous-time sigma delta modulator (CT-DSM) based neuro-recording interface circuit. This circuit consists of a current-reuse fully differential OTA, a voltage-controlled oscillator (VCO), a counter-based quantizer and a capacitive DAC feedback circuit with Data Weighted Averaging (DWA) logic. A current-reuse G m cell is adopted to suppress the input-referred noise with high energy efficiency. The VCO converts the input signal amplitude into phase for integration as well as quantization by the counter-based quantizer. The DAC feedback circuit ensures a linear operation of Gm-VCO within the input range. The prototype circuit is designed and implemented in a commercial 40-nm CMOS process. the proposed circuit consumes 19.5 $\mu$ W under 1.2-V supply voltage. With the maximum tolerable input swing of 100-mV pp , the proposed circuit achieves an SNDR of 59 dB over a bandwidth of 10 kHz. The proposed design is suitable for application such as the neuro-recording circuit in the closed-loop neural stimulation system.

A BJT-Based Temperature Sensor in 40-nm CMOS With ±0.8°C(3σ) Untrimmed Inaccuracy

Abstract: This paper presents a bipolar junction transistor (BJT) based temperature sensor in 40-nm CMOS process with improved untrimmed accuracy. By exploiting the relation between saturation current and recombination current at the base of BJT, the combined base current is optimized to compensate the process spread of base-emitter voltage (V BE ). In addition, a robust MOS resistor is proposed to further reduce the variations in the collector current as well as the VBE. Compared to the conventional weighted combination of resistors with complementary temperature coefficient, the proposed MOS resistor can reduce the variations by 3.2$\times$. An energy-efficient incremental ADC (IADC) digitizes the temperature dependent $V_{B E}$ and $\Delta V_{B E}$. The prototype achieves an untrimmed inaccuracy of $\pm 0.8^{\circ} \mathrm{C}(3 \sigma)$ at $1 \mathrm{kSa} / \mathrm{s}$ over -20$^{\circ}\mathbf{C}\sim\mathbf{100}^{\circ}\mathbf{C}$. The sensor draws $11.2 \mu\mathbf{A}$ at room temperature under $1.2-\mathrm{V}$ supply, making it a promising candidate for application in systems-on-chip (SoC) thermal monitoring.

Tunneling junction structure of perovskite/perovskite two-end laminated solar cell

Abstract: The invention discloses a tunneling junction structure of a perovskite/perovskite two-end laminated solar cell and application thereof. The tunneling junction structure comprises a tunneling compositelayer, a compact layer is arranged on one side of the tunneling composite layer, a transmission layer is arranged on another side of the tunneling composite layer, and the tunneling composite layer is made of a metal material. The tunnel junction structure of the invention can effectively reduce the open-circuit voltage loss of a laminated cell, a filling factor of the perovskite/perovskite laminated solar cell is improved, the photoelectric conversion efficiency of the perovskite/perovskite two-end laminated solar cell is improved, the preparation process is simple, the cost is low, and thetunneling junction structure is suitable for large-area industrial scale production.

Integrated Temperature Sensor with CMOS Relaxation Oscillator Based Sensor Interface for Biomedical Sensing

Abstract: A novel relaxation oscillator based sensor interface for high precision biomedical temperature sensor system is presented. It achieves low phase noise via swing boosting and inverter-based comparator. A commercial 65-nm CMOS process is adopted as the design environment. In the post-layout simulation, it oscillates at 3. 12MHz under 1V supply, consuming $16.6\mu W$. The phase noise is -112dBc/Hz and the Figure of Merit (FOM) is 160.3dBc/Hz. The post layout results render the proposed design a good candidate for high-precision temperature sensor interface.

Lead-tin blended perovskite layer and preparation method and application thereof

Abstract: The invention discloses a lead-tin blended perovskite layer and a preparation method and an application thereof. The lead-tin blended perovskite layer is prepared by adding a stabilizer into a lead-tin blended perovskite precursor solution, wherein the stabilizer is a metal reducing agent. By adding the reducing metal powder into the perovskite precursor solution, the oxidation of divalent tin ions in the lead-tin blended perovskite precursor solution is effectively inhibited, the quality of the lead-tin blended perovskite layer is improved, and the defect state density is reduced, so that thephotoelectric conversion efficiency of the solar cell is improved.