An 80-GHz DCO based on modified hybrid tuning banks is introduced in this paper. To achieve sub-MHz frequency resolution with reduced circuit complexity, the improved circuit topology replaces the conventional circuit topology with two binary-weighted SC cells, enabling eight SC-cell-based improved SC ladders to achieve the same fine-tuning steps as twelve SC-cell-based conventional SC ladders. To achieve lower phase noise and smaller chip size, the promoted binary-weighted digitally controlled transmission lines (DCTLs) are used to implement the coarse and medium tuning banks of the DCO. Compared to the conventional thermometer-coded DCTLs, control bits of the proposed DCTLs are reduced from 30 to 8, and the total length is reduced by 34.3% (from 122.76 to 80.66 μm). Fabricated in 40-nm CMOS, the DCO demonstrated in this work features a small fine-tuning step (483 kHz), a high oscillation frequency (79-85 GHz), and a smaller chip size (0.017 mm²). Compared to previous work, the modified DCO exhibits an excellent figure of merit with an area (FoM_A) of -198 dBc/Hz.

This paper describes a promising route for the exploration and development of 3.0 THz sensing and imaging with FET-based power detectors in a standard 65 nm CMOS process. Based on the plasma-wave theory proposed by Dyakonov and Shur, we designed high-responsivity and low-noise multiple detectors for monitoring a pulse-mode 3.0 THz quantum cascade laser (QCL). Furthermore, we present a fully integrated high-speed 32×32-pixel 3.0 THz CMOS image sensor (CIS). The full CIS measures 2.81×5.39 mm² and achieves a 423 V/W responsivity (Rv) and a 5.3 nW integral noise equivalent power (NEP) at room temperature. In experiments, we demonstrate a testing speed reaching 319 fps under continuous-wave (CW) illumination of a 3.0 THz QCL. The results indicate that our terahertz CIS has excellent potential in cost-effective and commercial THz imaging and material detection.

Two-dimensional transition metal dichalcogenides (TMDs) have intriguing physic properties and offer an exciting platform to explore many features that are important for future devices. In this work, we synthesized monolayer WS₂ as an example to study the optical response with hydrostatic pressure. The Raman results show a continuous tuning of the lattice vibrations that is induced by hydrostatic pressure. We further demonstrate an efficient pressure-induced change of the band structure and carrier dynamics via transient absorption measurements. We found that two time constants can be attributed to the capture process of two kinds of defect states, with the pressure increasing from 0.55 GPa to 2.91 GPa, both of capture processes were accelerated, and there is an inflection point within the pressure range of 1.56 GPa to 1.89 GPa. Our findings provide valuable information for the design of future optoelectronic devices.

In this work, we developed a simple and direct circuit model with a dual two-diode model that can be solved by a SPICE numerical simulation to comprehensively describe the monolithic perovskite/crystalline silicon (PVS/c-Si) tandem solar cells. We are able to reveal the effects of different efficiency-loss mechanisms based on the illuminated current density-voltage (J-V), semi-log dark J-V, and local ideality factor (m-V) curves. The effects of the individual efficiency-loss mechanism on the tandem cell’s efficiency are discussed, including the exp(V/V_T) and exp(V/2V_T) recombination, the whole cell’s and subcell’s shunts, and the ohmic-contact or Schottky-contact of the intermediate junction. We can also fit a practical J-V curve and find a specific group of parameters by the trial-and-error method. Although the fitted parameters are not a unique solution, they are valuable clues for identifying the efficiency loss with the aid of the cell’s structure and experimental processes. This method can also serve as an open platform for analyzing other tandem solar cells by substituting the corresponding circuit models. In summary, we developed a simple and effective methodology to diagnose the efficiency-loss source of a monolithic PVS/c-Si tandem cell, which is helpful to researchers who wish to adopt the proper approaches to improve their solar cells.

The stability of organic solar cells (OSCs) remains a major concern for their ultimate industrialization due to the photo, oxygen, and water susceptibility of organic photoactive materials. Usually, antioxidant additives are blended as radical scavengers into the active layer. However, it will induce the intrinsic morphology instability and adversely affect the efficiency and long-term stability. Herein, the antioxidant dibutylhydroxytoluene (BHT) group has been covalently linked onto the side chain of benzothiadiazole (BT) unit, and a series of ternary copolymers D18-Cl-BTBHTx (x = 0, 0.05, 0.1, 0.2) with varied ratio of BHT-containing side chains have been synthesized. It was found that the introduction of BHT side chains would have a negligible effect on the photophysical properties and electronic levels, and the D18-Cl-BTBHT0.05: Y6-based OSC achieved the highest power conversion efficiency (PCE) of 17.6%, which is higher than those based active layer blended with BHT additives. More importantly, the unencapsulated device based on D18-Cl-BTBHTx (x = 0.05, 0.1, 0.2) retained approximately 50% of the initial PCE over 30 hours operation under ambient conditions, significantly outperforming the control device based on D18-Cl (90% degradation in PCE after 30 h). This work provides a new structural design strategy of copolymers for OSCs with simultaneously improved efficiency and stability.

Gallium oxide (Ga₂O₃) based flexible heterojunction type deep ultraviolet (UV) photodetectors show excellent solar-blind photoelectric performance, even when not powered, which makes them ideal for use in intelligent wearable devices. However, traditional flexible photodetectors are prone to damage during use due to poor toughness, which reduces the service life of these devices. Self-healing hydrogels have been demonstrated to have the ability to repair damage and their combination with Ga₂O₃ could potentially improve the lifetime of the flexible photodetectors while maintaining their performance. Herein, a novel self-healing and self-powered flexible photodetector has been constructed onto the hydrogel substrate, which exhibits an excellent responsivity of 0.24 mA/W under 254 nm UV light at zero bias due to the built-in electric field originating from the PEDOT: PSS/Ga₂O₃ heterojunction. The self-healing of the Ga₂O₃ based photodetector was enabled by the reversible property of the synthesis of agarose and polyvinyl alcohol double network, which allows the photodetector to recover its original configuration and function after damage. After self-healing, the photocurrent of the photodetector decreases from 1.23 to 1.21 μA, while the dark current rises from 0.95 to 0.97 μA, with a barely unchanged of photoresponse speed. Such a remarkable recovery capability and the photodetector’s superior photoelectric performance not only significantly enhance a device lifespan but also present new possibilities to develop wearable and intelligent electronics in the future.

A NiO/β-Ga₂O₃ heterojunction-gate field effect transistor (HJ-FET) is fabricated and its instability mechanisms are experimentally investigated under different gate stress voltage (V_G,s) and stress times (t_s). Two different degradation mechanisms of the devices under negative bias stress (NBS) are identified. At low V_G,s for a short t_s, NiO bulk traps trapping/de-trapping electrons are responsible for decrease/recovery of the leakage current, respectively. At higher V_G,s or long t_s, the device transfer characteristic curves and threshold voltage (V_TH) are almost permanently negatively shifted. This is because the interface dipoles are almost permanently ionized and neutralize the ionized charges in the space charge region (SCR) across the heterojunction interface, resulting in a narrowing SCR. This provides an important theoretical guide to study the reliability of NiO/β-Ga₂O₃ heterojunction devices in power electronic applications.

We demonstrate superb large-area vertical β-Ga₂O₃ SBDs with a Schottky contact area of 1 × 1 mm² and obtain a high-efficiency DC–DC converter based on the device. The β-Ga₂O₃ SBD can obtain a forward current of 8 A with a forward voltage of 5 V, and has a reverse breakdown voltage of 612 V. The forward turn-on voltage (V_F) and the on-resistance (R_on) are 1.17 V and 0.46 Ω, respectively. The conversion efficiency of the β-Ga₂O₃ SBD-based DC–DC converter is 95.81%. This work indicates the great potential of Ga₂O₃ SBDs and relevant circuits in power electronic applications.