Open-circuit Voltage Research Articles

Photocurrent switching effect and visible light activity of electrochemically synthesized bifunctional through oxide via TiO2/CuO composites

Photoelectrochemical conversion of solar energy into fuel products such as H2 or CH4 is an appealing, but technologically difficult process due to the simultaneous requirements for stability, efficiency and selectivity in the photoelectrode. One approach to design a photoelectrode with suitable properties is by using different materials that can complement each other. In this study, we introduce a novel approach by compositing TiO2 with CuO via electrodeposition of Cu into through-oxide vias/channels – a design that offers enhanced synergy between the materials. The Cu is then precisely transformed into Cu2O, CuO, or a mixture, based on annealing temperature, enabling tunable properties and optimized functionality. Unlike in traditional “sandwich” composites, this structuring reduces bulk charge carrier recombination through the formation of a depletion zone between TiO2 and CuO, allowing both materials to perform distinct functions. As a result, photocurrent switching is achieved by altering the applied potential, which is a functionality not previously demonstrated for photoactive composite materials. Our study also reports evidence of visible light sensitivity in TiO2/CuO composites when illuminated by a 4100K LED without UV components. Open circuit voltage decay measurements reveal that the improved charge carrier transport is due to the formation of a conductive Cu pathway—a novel finding that opens new possibilities for efficient photoexcitation. Although the charge carrier lifetimes were found to be shorter in TiO2/CuO electrodes compared to pure TiO2, we attribute this to the phenomenon of Cu "filling" the TiO2 channels and decreasing the available surface area, a trade-off that provides crucial insights into material design for future applications.

Tuning the bandgap without compromising efficiency: ambient solution processing of Ge-alloyed (Ag,Cu)2Zn(Sn,Ge)(S,Se)4 kesterite thin-film solar cells

The photovoltaic sector currently experiences a growing demand for deeply-integrated technologies in agriculture, buildings, vehicles, among others. Kesterite compounds provide a versatile solution through their tunable bandgap via isovalent alloying. However, this should be done while preserving material opto-electronic quality and device performance, which is an unresolved challenge. Indeed, tuning the bandgap of kesterites must ensure low crystalline disorder to counteract the associated open-circuit voltage (Voc) losses when used in solar cells. To achieve this goal, this work introduces a simple molecular ink recipe realized in ambient air to process single-phase high-quality Ag,Gealloyed kesterite absorbers. By varying the Ge content from 0 to 100%, the absorber bandgap covers the range from 1.15 to 1.5 eV, in which the Urbach energy remains close to 20 meV and promisingly low Voc deficits are observed. In particular, the champion efficiency of 12.1% obtained with 40% Ge breaks the record for Ge-alloyed kesterites with a 1.2 eV bandgap by remarkably reaching 62% of the Shockley-Queisser limit for Voc. This study demonstrates a promising strategy to solve the issue of large band tailing and low opto-electronic quality in widebandgap kesterites while establishing a foundation for solution-processed kesterite solar cells with tunable bandgap and promising performance.

Ag,Cd double gradient doping at front interface for high efficiency CZTSSe solar cells

Kesterite Cu2ZnSn(S,Se)4 (CZTSSe) solar cells have attracted considerable attention in recent years, and considered to be potential alternative solutions to existing commercialized solar cells for future energy demands. However, poor-quality p-n junction causes severe carrier recombination at the front interface, resulting high open-circuit voltage deficit and unsatisfactory efficiency of CZTSSe solar cells. In this work, Ag,Cd double gradient doping was introduced to front interface for interface carrier recombination suppression. Benefited from the formed Ag,Cd double gradient, defect and/or defect cluster at front interface significantly reduced, thus evidently suppressing the carrier recombination at front interface. As a result, the power conversion efficiency (PCE) of champion device increased from 10.04 % (Reference) to 12.66 % (With Ag,Cd). This Ag,Cd double gradient architecture offers new ideas for improvement of high efficiency CZTSSe as well as other solar cells.

Employing the pyroelectric effect in LiTaO3 thin film for infrared detection of complex gases

Abstract In this paper, the lithium tantalite ( LiTaO 3 ) thin film has been employed as the highly sensitive element for infrared detection of compound (refrigerant) gases such as 1,1,1,2-Tetrafluoroethane ( C 2 H 2 F 4 ) and 1,1,1,2,3,3,3-Heptafluoropropane ( C 3 F 7 H ). The LiTaO 3 thin film was subjected to the mid-infrared light from output transmission spectra of C 2 H 2 F 4 as well as C 3 F 7 H molecules used as sources. The technology for preparation of LiTaO 3 thin film as well as detector design and manufacturing are presented. Particular attention was paid to production of conductive electrodes, including a very thin semitransparent Au layer evaporated on the top surface of LiTaO 3 pyroelectric material. Important characteristics of the LiTaO 3 based pyroelectric system are briefly discussed. Additionally, the design, construction, and performance of the gas chamber operating as a channel for gas sensor testing is briefly described. The pyroelectric open-circuit voltage generated in LiTaO 3 was boosted with a signal processing circuit for selective high-sensitivity detection of compound gases at room temperature. The infrared (IR) filters such as titanium dioxide ( TiO 2 ) and zinc oxide ZnO having narrow bandwidth and working at a normal incidence were integrated into a compact and portable pyroelectric micro-sensor before the LiTaO 3 pyroelectric element in the same package for cleaning background in a broad IR spectrum of both refrigerant gases. The performance, stability, and accuracy of fabricated LiTaO 3 -based IR gas sensors operating on the pyroelectric open-circuit voltage were tested and improved. IR gas sensors designed and prepared in this study can be utilized for non-contact, sensitive, and selective detection of highly hazardous and explosive gases.

Scalable Fabrication of Flexible Thermoelectric Generator with Non-Toxic Ga:ZnO and PEDOT:PSS Thermoelements for Wearable Energy Harvesting

This study presents a lightweight, flexible thermoelectric generator (TEG) designed for sustainable energy harvesting in wearable electronics. The TEG integrates p-type PEDOT:PSS and n-type Ga:ZnO thermoelements, utilizing scalable drop-casting and 3D-printing techniques to address key concerns of sustainability, scalability, and safety. Unlike conventional TEGs that rely on toxic or rare-earth materials, this device employs predominantly earth-abundant, non-toxic components, offering a more cost-effective and environmentally friendly alternative. Structural analysis using FE-SEM and EDX revealed a relatively dense microstructure with uniform elemental distribution in the free-standing thermoelements, contributing to the device’s mechanical flexibility and performance stability. The TEG, consisting of five thermoelement pairs, achieved a peak open-circuit voltage of 0.111mV and a power output of 0.123 nW at a temperature difference (ΔT) of 10K, demonstrating performance competitive with TEGs fabricated using more complex and expensive methods. When tested on a human wrist, the TEG generated 0.230 nW at a ΔT of 17K, outperforming other wearable TEGs, with power increases observed during body movement. Additionally, the device maintained stable resistance at a 90° bending angle, enhancing its ability to conform to the body’s shape for improved energy harvesting and efficiency. While the power output can be further improved, this TEG represents a notable advancement in flexibility, scalability, and the use of eco-friendly, cost-effective materials and fabrication methods. Addressing these critical challenges in wearable thermoelectrics paves the way for future self-powered health monitoring, fitness tracking, and environmental sensing applications.

A comprehensive optimization of highly efficient MA-Free wide-bandgap perovskites for 4-T Perovskite/Silicon tandem solar cells

Perovskite/silicon tandem solar cells have emerged as a highly promising strategy for surpassing the Shockley–Queisser limit. Among these tandem solar cells, the wide-bandgap perovskite plays a key role in highly efficient tandem solar cells. However, the wide bandgap perovskite material suffers from considerable voltage loss due to a high trap density and phase instability under light illumination. In this study, we present a comprehensive set of optimization procedures designed to enhance the power conversion efficiency of methylammonium-free (MA-free) wide-bandgap perovskites. Following this procedure, the opaque MA-free wide-bandgap perovskite solar cells demonstrate an impressive efficiency of 22.11 % with a minimal open-circuit voltage deficit of 0.47 V. Moreover, the efficiency of the semi-transparent wide-bandgap perovskite solar cells reached 19.21 %, and these semi-transparent cells were subsequently integrated into a 4-terminal perovskite/Si tandem solar cell, yielding a remarkable efficiency of 29.98 %. Our study paves a facile way towards highly efficient wide-bandgap perovskite solar cells for the application of semi-transparent and tandem solar cells.

Bifunctional MA3Bi2I9 towards solar energy conversion and storage for all-solid-state photo-rechargeable battery

Recent endeavors have concentrated intensively on the integration and storage of solar energy within a singular apparatus. However, at present, these apparatuses are confronted with issues such as complicated fabrication processes, complex structures, and electrolyte leakage. In this study, an all-solid-state photo-rechargeable battery is presented, utilizing TiO2 as the photoanode, MA3Bi2I9 as the photoelectric conversion and energy storage active material layer, and Pt as the counter electrode. The assembled device can remain an open-circuit voltage of 0.35 V in the dark state. Devices connected in series can power a LED for up to 2 min. Furthermore, this photo-rechargeable battery demonstrates commendable stability over a storage period of 60 days under ambient conditions. Simultaneously, electrochemical analyses corroborate that the charge-discharge mechanism of the device is intimately associated with the redox processes of Bi ions. This study proposes novel approaches for the design of innovative energy devices that integrate photovoltaic charging and energy storage.

Impact of Self-Assembled Monolayer Structural Design on Perovskite Phase Regulation, Hole-Selective Contact, and Energy Loss in Inverted Perovskite Solar Cells

Recent studies have shown that self-assembled molecule (SAM)-based hole-selective contacts (HSCs) offer a promising solution to the challenges faced by perovskite solar cells (PVSCs), including minimal material consumption, scalable production, high interface stability, and the use of environmentally friendly solvents. In this study, the efficacy of two designs of SAMs (Cz and PA) as HSCs in inverted PVSCs was investigated by comparing them with the conventional MeO-2PACz (MeO) SAM. Surface analyses showed that the surface of PA is smoother than that of Cz, which helps to reduce interfacial defects. Subsequent perovskite deposition exhibited a reduced formation of the PbI2 phase, incidiating that its phase modulation ability is superior to that of MeO. Further analyses demonstrate the superior charge extraction ability of PA as a result of reduced interfacial defects and non-radiative recombination at the HSC/perovskite interface. By further coupling with phenethylammonium iodide (PEAI) surface passivation, both interfaces of the perovskite film were optimized and the inverted ((FAPbI3)0.85(MAPbBr3)0.15)0.95(CsPbI3)0.05 (bandgap = 1.62eV) PVSC achieves a high power conversion efficiency (PCE) of 23.3% and a very high open-circuit voltage of 1.227V due to the largely reduced energy loss. In addition, the PA PVSC exhibits enhanced long-term thermal stability at 85°C in a nitrogen atmosphere.

Optimizing the CBO for Improved Performance in the PBDB-T: ITIC Organic Photovoltaic Cell

Renewable energy sector should have power generation system which are environmentally friendly as well as ecofriendly. In respect of this we present theoretical and simulation-based study of an organic solar cell with the absorber layer PBDB-T and ITIC blend. Transportation of photogenerated charge carriers in the solar cells plays vital role in determining the performance parameters of the cells. In view of improving the charge carrier transportation in the proposed solar cell we propose conduction band optimization (CBO) method. Further the impact of the physical parameters such as temperature, series and shunt resistances are also observed for the better understanding of the performance of the proposed solar cell device. All the work presented is performed via the SCAPS 1d simulation software. First, the conduction band optimization is done by the realization of the electron affinity of all the layers of the proposed solar cell. The CBO optimization shows that the proposed cell can have best performance with the efficiency of 21.73%. This optimum performance of the cell obtained at the 3.8eV electron affinity of the absorber layer. Moreover, the physical parameters optimization revealed the suitable condition of superior performance. The appropriate physical conditions are obtained as series and shunt resistances of 3.5 and 1000 Ωcm2 at temperature of 300K. The optimum performance is as power conversion efficiency (PCE) of 17.39%, fill factor (FF) of 65.61% with the open circuit voltage (Voc) and short circuit current (Jsc) of 0.9561 V and 27.72 mA/cm2 respectively. This shows the best performance in the organic family of photovoltaic cells.

Highly robust and efficient metal-free water cup solid–liquid triboelectric nanogenerator for water wave energy harvesting and ethanol detection

Recently, low-frequency mechanical energy harvesters based on solid–liquid contact electrification have garnered widespread attention for their unique advantages in wear resistance, high charge transfer efficiency, and novel insights into electron–ion interactions at the solid–liquid interface, particularly in material identification. Hence, we designed an robust and efficient water cup triboelectric nanogenerator (WC-TENG) that only uses ordinary drinking water and plastic water cups as primary materials, achieving high-efficiency power output while eliminating the need for metal electrodes and effectively addressing the issue of corrosion in generator components. Experimental results indicate that, at an operating frequency of 2 Hz, the WC-TENG generates an open-circuit voltage (Voc) of 249.71 V, a short-circuit current (Isc) of 4.21 µA, and a transferred charge (Qsc) of 188.85 nC. The WC-TENG is capable of harvesting water wave energy with low frequency and low vibration amplitude. Furthermore, the introduction of ethanol disrupts the potential balance at the solid–liquid interface by impeding electron transfer and reducing the WC-TENG’s electrical output, but as the ethanol volatilizes, the device gradually returns to its original potential state, demonstrating its potential as a selective ethanol sensor. This design not only advances the development of corrosion-resistant, high-performance energy harvesters but also opens up new possibilities for low-cost, sustainable, and environmentally adaptable sensing technologies.

Design and performance analysis of novel perovskite/CZTSe hybrid solar cell for high efficiency

With newer developments, the solar cells in the market need to be more efficient, affordable, stable, and environment friendly. The perovskite solar cells have already shown very impressive progress in performance since their inception. It has already reached 26 % efficiency and is expected to reach more, owing to its stupendous photovoltaic nature. On the other hand, even with a very high absorption coefficient, the CZTSe solar cell has not crossed the 15 % efficiency mark. Looking at the characteristics of both the materials and considerable differences in band gap, a novel hybrid structure, HTL/Perovskite/CZTSe/CdS/ZnO, has been proposed in this work to implement Perovskite (CH3NH3Pb3−xClx) and CZTSe layer to absorb higher energy and lower energy photons respectively. In this context, choosing a proper Perovskite material becomes more crucial to have the required band alignment for the easy transportation of the excitons. The performance of the cell has been observed in varying parameters like thickness, doping, defects, and temperature. A high efficiency of 30.9 % is achieved which is much higher than the contemporary solar cells. Several other output parameters like Short Circuit Current Density (JSC), Open Circuit Voltage (VOC), Fill-Factor (FF%) characteristics have also been discussed.

Bridged Carbolong Modulating Interfacial Charge Transfer Enhancement for High-Performance Inverted Perovskite Solar Cells.

Efficient regulation of perovskite/C60 interface is crucial to improving the long-term stability of the inverted perovskite solar cells (PSCs). However, precise methods for controlling the perovskite/C60 interface have yet to be thoroughly explored. Herein, we develop a carbolong chemical manipulation strategy to improve the interface contact of perovskite/C60 due to versatile functional groups and excellent optoelectronic properties of carbolong metallaaromatics. And constructing an electron-transfer bridge enhances the interfacial interaction and accelerates interfacial electron transfer. The carbolong manipulation results in optimized energy level alignment, suppressed nonradiative recombination, and improved electronic contact. An impressive efficiency of 25.80% is demonstrated, with open-circuit voltage and fill factor of 1.19 V and 84.53%, respectively. The unsealed devices retain more than 98% of their original efficiency after 1400 h of maximum power point tracking under illumination and demonstrate remarkable thermal stability, maintaining 93% of their initial efficiency after 2500 h at 85°C in a nitrogen atmosphere. And the encapsulated carbolong-modified module achieved a high efficiency of 20.72% (active area of 25.25 cm²) with robust operation stability.

A Triboelectric Nanogenerator Based on TPU/PLA for Basketball Motion Monitoring.

Sports monitoring equipment that integrates advanced sensing technology has attracted widespread attention in recent years. Hence, we proposed a TPU/PLA 3D printing film triboelectric nanogenerator (TP-TENG) to monitor basketball player posture for training effectiveness evaluation. By introducing carbon fibers, TPU/PLA/Carbon film with conductive and positive triboelectric properties was prepared. According to results, the peak power density is 58.38 mW m-2 when the load resistance of 30 MΩ is matched. Nevertheless, when TP-TENG encounters wrinkles and continues to work for a period of time, its output performance will tend to stabilize. And the open-circuit voltage (VOC), transfer charge (QSC), and short-circuit current (ISC) increase to 91 %, 92 %, and 92 %, respectively, almost the same as their original values. Furthermore, the TP-TENG sensor can recognize human posture in different basketball motion posture, including skipping, squatting, walking, running. This work can help to promote the application of 3D printing TENG in basketball sports monitoring.

A Wearable Triboelectric Nanogenerator Based on Polyester-Paper Cloth for Mechanical Energy Harvesting and Running Motion Sensing.

Paper-based triboelectric nanogenerators (P-TENGs) have recently garnered significant attention in wearable electronics. However, traditional P-TENGs are constrained by the inherent strength limitations of paper. Hence, we reported a novel polyester-paper cloth-based triboelectric nanogenerator (PP-TENG) designed for mechanical energy harvesting and running motion monitoring. Compared to paper, polyester-paper cloth has higher durability and tear resistance. The PP-TENG capitalizes on the unique fluffy internal structure of polyester-paper cloth, imparting high sensitivity to pressure variations. Experimental results demonstrate that the PP-TENG achieves an open-circuit voltage (Voc) of 466.64 V, a short-circuit current (Isc) of 48.73 μA, and a transfer charge (Qsc) of 90 nC. Its maximum output power reaches 930.26 μW when connected to a 40 MΩ load. These impressive metrics underscore the potential of PP-TENG in energy harvesting applications, particularly for wearable electronic devices. The device's integration into the soles of athletic socks showcases its practical utility, providing real-time monitoring of runners' gait and step count. This integration not only enhances the functionality of sportswear but also offers valuable data for performance analysis and injury prevention, marking a significant advancement in wearable technology and intelligent textiles. This research provide a promising path for self-powered wearable sensors and flexible electronics applications.

Weavable, Reconfigurable Triboelectric Ferrofluid Fiber for Early Warning.

As communication technologies have become omnipresent, the prevalence of electromagnetic field (EMF) exposures poses possible health risks, particularly to vulnerable groups such as pregnant women. In response, we introduce a triboelectric ferrofluid fiber (TFF) that moves in response to EMF, thereby generating charge in a way that is self-powered. The TFF is flexible, stretchable (470%), and can be woven into fabrics. The TFF utilizes a soft-contact (ferrofluid-silicon rubber fiber) triboelectric core layer to enhance its sensitivity to EMF, enabling it to detect even minor electromagnetic fluctuations, such as those from cell phone typing. By integrating hydrogel electrodes that offer conductivity and minimal electromagnetic interference shielding, the TFF's sensitivity to magnetic fields is further amplified. Moreover, its open-circuit voltage output is increased by 50% compared to the conventional electrodes. Building on this technology, we designed a smart fabric for environmental early warning and potential real-time pulse monitoring, specifically tailored for the safety and healthcare needs of vulnerable groups. Finally, we developed a sensing and communication apparel (SCA) by integrating TFF into the apparel and exploring its capabilities in a wireless transmission of warning signals and long-distance NFC functionality.

Photovoltaic Performance Improvement of Dilute Nitrides GaAs<sub>1-<i>x</i></sub>N<sub><i>x </i></sub>-Based Thin-Film Solar Cell Structure Using SCAPS-1D Software

The recent industrial revolution has increased the demand for the possible use of renewable energy sources to meet the World’s high energy requirements and to minimize the quantity of green-house gases (GHGs) in the atmosphere at once in a sustainable manner. Solar energy is one of the renewable energy sources that has garnered the most attention for sustainable energy production because it is ecologically benign, clean as well as widely available. The main issue with solar cells in comparison to traditional systems, however, continue to be their greater cost and efficiency restriction. It is anticipated that the issues will be resolved as the technology progresses as well as precious fabricating materials are used more. Dilute nitrides compound semiconductors, such as GaAs<sub>1-<i>x</i></sub>N<sub><i>x</i></sub>, GaP<sub>1-<i>x</i></sub>N<sub><i>x</i></sub> and Ga<sub>y</sub>In<sub>1-<i>y</i></sub>As<sub>1-<i>x</i></sub>N<sub><i>x</i></sub> have become promising materials because they have unique properties suitable for novel next generation optoelectronics especially photovoltaic applications. In addition, among dilute nitrides, GaAs<sub>1-<i>x</i></sub>N<sub><i>x</i></sub> attracts much attention to the researchers because of its excellent absorption coefficients and charge-transport properties, which are importantly desirable for high efficiency solar cell. Therefore, in this research work, the thin-film solar cell’s performance metrics with dilute nitrides GaAs<sub>1-<i>x</i></sub>N<sub><i>x </i></sub>as absorber layer were investigated by <I>SCAPS-1D</I>. The impacts of bandgap bowing and absorber layer’s thickness as well as operating temperatures, work functions of back-contact were evaluated to optimize open-circuited voltage (V<sub>oc</sub>), short-circuited current density (J<sub>sc</sub>), fill-factor (FF) and efficiency (η). The absorber layer’s bandgap dependence performances study revealed that efficiency around 46% can be achieved with exceptional feasibilities such as lower density of as-grown defects and reliable lifetime by tuning bandgap to 0.82eV via adjusting nitrogen concentration in GaAs<sub>1-<i>x</i></sub>N<sub><i>x</i></sub>. The assessment of performance for different absorber layer thicknesses showed that thickness around 2000nm is ideal for improving the suggested solar cell efficiency. Furthermore, higher efficiency and optimized other performance parameters obtaining at temperature 300K suggested that it is preferable to run the solar cell at that temperature to ensure steady-state functioning. Finally, it was explored by evaluating dependence of V<sub>oc</sub>, J<sub>sc</sub>, FF and η on back-contact work functions at two bandgap energies of absorber layer that specially J<sub>sc</sub> was dramatically influenced with changing bandgap of absorber layer. The research findings would be helpful for emerging renewable energy-based nanotechnology for reducing the world higher energy crisis and green-house gases at once in a sustainable manner.

Quantum chemical study of new oxadiazoles as efficient optical and nonlinear optical and photovoltaic materials under gas, PCM and COSMO solvent effects

The science of organic optical and nonlinear optical (NLO) materials has been captivating the scientific community owing to their extensive applications in optoelectronics, OLEDs, and telecommunications. This study presents the design and investigation of novel organic compounds of pyrene and 1,3,4-oxadiazole derivatives (1-oxza to 6-oxza), featuring various push–pull combinations. Quantum chemical calculations were employed to determine linear polarizabilities (α) and third-order NLO polarizabilities (γ). Notably, the largest average third-order NLO polarizability value was found to be 254.9 × 10−36 esu for the finely tuned push–pull system 6-oxza, which is ∼35 times greater than that of the prototype NLO molecule of p-nitroaniline (p-NA). Among the derivatives, 1-oxza exhibits the highest linear isotropic polarizability (αiso) value of 61.59 × 10−24 esu, while 5-oxza displays the highest linear anisotropic polarizability (αaniso) value of 60.09 × 10−24 esu. A notable increase of approximately ∼1 to ∼2 times in < γ > is observed for selected compounds (1-oxza, 4-oxza, 6-oxza), indicating that the Conductor-like Screening Model (COSMO) overestimates the values compared to the polarizable continuum model (PCM) and gas phases. Solvent significantly enhances third-order NLO polarizability amplitudes depending upon solvent polarity and strength of substitution groups. We calculated the frequency-dependent third-order NLO polarizability of 6-oxza at laser wavelengths ranging from 1400 to 1970 nm. The second hyperpolarizability EFISHG process (γ(−2ω; ω, ω, 0)) was calculated at a laser wavelength of 1400 nm, and the γ-amplitude was found to be 400.1 × 10−36 esu. The remarkable hyperpolarizability response in the gas phase is corroborated by TD-DFT calculations, which reveal a larger transition dipole moment of 3.062 and a lower transition energy of 3.780 eV as origin of larger hyperpolarizability for 6-oxza. A comprehensive analysis was performed based on FMOs for designed compounds to elucidate the intramolecular charge transfer (ICT) mechanisms and observed a notable reduction in energy band gap 4.89 eV for 6-oxza, which is responsible for enhanced NLO response. Additionally, DOS maps revealed the quantitative contributions of HOMOs and LUMOs for crucial electronic states related to the efficient ICT process. Additionally, we analyzed the photovoltaic properties and found that 6-oxza has the highest dye regeneration and the lowest open-circuit voltages of 1.89 eV and 2.22 eV, respectively. Our designed model compounds can put real-time such compounds under spotlight of scientific interests which seeks more efficient optical and NLO properties.

Highly efficient narrow bandgap Cu(In,Ga)Se2 solar cells with enhanced open circuit voltage for tandem application

Although an ideal bandgap matching with 0.96 eV and 1.62 eV for a double-junction tandem is hard to realize practically, among all mature photovoltaic systems, Cu(In,Ga)Se2 (CIGSe) can provide the closest bandgap of 1.00 eV for the bottom sub-cell by adjusting its composition. However, pure CuInSe2 (CISe) solar cell suffers strong interfacial carrier recombination. We hereby present approaches to introduce appropriate Ga gradients in both the back and front parts of absorber while maintaining the absorption spectrum close to CISe. With an appropriate front Ga gradient, the open circuit voltage can be enhanced by ~30 mV. With a pre-deposited CIGSe layer and a high copper excess deposition during absorber growth, the Ga diffusion can be well suppressed and a wide U-shaped Ga grading with a minimum bandgap of 1.01 eV has been created. Our optimized narrow-bandgap CIGSe solar cell has achieved a certified record PCE of 20.26%, with a record-low open circuit voltage deficit of 368 mV and a record-high contribution of 10% absolute efficiency to a four-terminal tandem. This work demonstrates the potential of controlling gallium diffusion to improve the performance of narrow bandgap CIGSe solar cells for tandem applications.

High-Performance Photodiodes Based on In-Situ Etched PbSe Colloidal Quantum Dots with Responses Extended to 2500 nm.

The performance of PbSe colloidal quantum dot (CQD) based photodiodes with responses beyond 2000 nm was far from satisfactory and has rarely been reported. The difficulty in obtaining chemically stable large-sized PbSe CQDs was the main reason. In this work, chloride ions in weak acidic solvent were introduced to in-situ etch out the Se atoms on the surfaces of PbSe CQDs and formed a -Pb-Cl protection layer. As a result, there were no longer any easily oxidized Se atoms exposed to the ambient environment. The mechanism behind our method for stabilizing PbSe CQDs was distinct from the commonly reported ones such as attaching new adlayers directly. The photodiodes with the etched PbSe CQDs achieved 0.75 A/W responsivity at λ = 2200 nm, 0.15 V open circuit voltage and 100% internal quantum efficiency without the assist of photoconductive gains, which were the best records for PbSe-based photodiodes working beyond 2000 nm.

Self-floating Janus hydrovoltaics for sustainable electricity generation

Water is widely available in nature that attracts increasing interesting in simulating transpiration effect to induce the electricity. However, it faces great challenges in establishing continues moisture gradient rather than periodic wetting behaviors. Here, we propose a self-floating Janus generator containing the hydrophilic and hydrophobic regions to induce the continues electricity. The self-floating and hydrophilic behavior ensures a continuous water supply. The asymmetric Janus structure forms a distinct wet/dry interface to create a significant water gradient with evaporation equilibrium state. At wetting region, the electric double layer (EDL) is formed due to the interaction of water and carbon black particles. Attributed to the large water gradient and fast contact line evaporation, proton accumulates across the capillary front that induces a potential difference. As a result, the Janus generator achieves 0.46 V open circuit voltage lasting for 40 h. It also demonstrates the potential applications of Janus generator in power supply, moisture detection and sweat monitoring et al. The proposed Janus generators show great potential in ocean energy development and be of great significance to the sensing of rescue signals in the sea.