Photoactive Area Research Articles

Comprehensive analysis of the performance of a microfluidic photoelectrochemical solar cell with heat exchanger

A dye-sensitized solar cell (DSSC) is a type of photoelectrochemical cell that converts sunlight directly into electricity using a photoanode with a dye-sensitized, nonporous semiconductor layer. This study investigates the impact of integrating microfluidic capabilities into DSSCs, resulting in a flow-cell configuration that introduces new electrical characteristics without compromising its performance. The primary goal of the work was to define and determine the values of heat, mass, and charge transport resistances, and to explore their relationships with the cell’s current–voltage characteristics, temperature, light intensity, and spectra. We employed both experimental methods and computational fluid dynamics using the Lattice-Boltzmann solver to analyze the cell’s dynamics. A novel multilayered microfluidic DSSC (µDSSC) was designed, featuring an innovative “gapless” configuration with a photoactive surface area exceeding 7 cm2, integrated directly with a microfluidic heat exchanger. This configuration allowed the µDSSC to achieve a power conversion efficiency (PCE) of at least 6 % under standard test conditions, with a fill factor reaching up to 68 %. By gradually covering the cell surface, the impact of series resistance (Rs) on PCE was minimized, enabling a maximum PCE of 19–22 %. A new integral definition of the fill factor (IFF) was proposed, which accurately describes the performance of cells constrained by ion mass transport resistance. For the gapless µDSSC, the IFF ranged from 58 % to 88 %. Additionally, we introduced a maximum cell efficiency (MCE) parameter to represent the cell’s efficiency at the theoretical limit of Rs = 0, determined to be 20.7 % for the gapless µDSSC. This MCE value is specific to the cell and is independent of the illuminated surface area and incident light intensity. The thermal efficiency of µDSSC cells is generally limited by heat conduction through the multilayer structure, but at practical cell surface temperatures of 50–80 °C, this limitation is 3 to 6 times less significant than the limitation imposed by the maximum solar energy flux reaching the cell surface. The integration of microchannels into the cell led to a 58 % reduction in hydraulic resistance along the main flow direction. While electrolyte flow typically reduces efficiency in wide-gap DSSCs, the gapless configuration minimizes mass transport resistance, ensuring that fluid flow does not adversely affect the performance of gapless µDSSCs.

Cu2O/TiO2 core–shell nanowire heterojunction for high-performance self-powered photodetector

High-performance self-powered photodetectors (PDs) have great commercial value in optical communication, intelligent sensing and medical diagnosis. However, the limited active area of traditional thin film heterojunction seriously restricts the photoelectric performance of the detector. In this paper, the Cu2O/TiO2 core-shell nanowire (NW) heterojunction PD was synthesized for the first time by simple hydrothermal and electrochemical deposition methods, which effectively improved the response performance and response speed of the device based on its broad photoactive area and ordered carrier transport path. The PD exhibits significant diode behavior, with rectification ratios of 543 at ±2 V. The responsivity is as high as 6.8 mA W−1 at zero bias under 490 nm illumination. The short rise and decay times measured are 0.09 and 0.18 s at zero bias, respectively. Obviously, this low-cost, high-performance self-powered Cu2O/TiO2 core-shell NW heterojunction PD shows great promise in future optoelectronic device applications.

Highly Efficient Monolithic Perovskite/Perovskite/Silicon Triple-Junction Solar Cells.

Wide-bandgap metal halide perovskites have demonstrated promise in multijunction photovoltaic (PV) cells. However, photoinduced phase segregation and the resultant low open-circuit voltage (Voc) have greatly limited the PV performance of perovskite-based multijunction devices. Here, a alloying strategy is reported to achieve uniform distribution of triple cations and halides in wide-bandgap perovskites by doping Rb+ and Cl- with small ionic radii, which effectively suppresses halide phase segregation while promoting the homogenization of surface potential. Based on this strategy, a Voc of 1.33V is obtained from single-junction perovskite solar cells, and a VOC approaching 3.0V and a power conversion efficiency of 25.0% (obtained from reverse scan direction, certified efficiency: 24.19%) on an 1.04 cm2 photoactive area can be achieved in a perovskite/perovskite/c-Si triple-junction tandem cell, where the certification efficiency is by far the greatest performance of perovskite-based triple-junction tandem solar cells. This work overcomes the performance deadlock of perovskite-based triple-junction tandem cells by setting a materials-by-design paradigm.

Toward Industrial Production of a High-Performance Self-Powered Ultraviolet Photodetector Using Nanoporous Al-Doped ZnO Thin Films.

Al-doped ZnO (AZO) thin films are effective n-type semiconductors for ultraviolet (UV) detection because of their low cost, high electron mobility, and high sensitivity to UV light, especially in the UVA spectrum. However, a reasonable compromise between performance (such as sensitivity, detectivity, and response time) and fabrication ease remains an obstacle to the practicability of AZO-based UV photodetectors. To address this issue, we propose an efficient strategy to achieve a large AZO photoactive area for outstanding performance, along with a facile sol-gel method. Consequently, the device exhibits a superb on/off ratio of >104, a high detectivity of 1.85 × 1012 Jones, and a fast response speed under 365 nm UVA illumination without external energy consumption. Hence, this study suggests a self-powered and high-performance nanoporous AZO-based UVA detector with an environmentally friendly scalable process that satisfies industrial production requirements for numerous practical UV-detection applications.

Boosting PFOA photocatalytic removal from water using highly adsorptive and sunlight-responsive ZIF67/MIL-100(Fe) modified C3N4

Per- and polyfluoroalkyl substances (PFAS) are widely used in many industrial and food processes. Their discharge into the environment shows a serious threat because of their toxicity, non-biodegradability and high mobility in water and soil. Photocatalytic reaction is confirmed an effective way for the degradation of PFOA. Photocatalytic materials with multifunctional properties can boost the generation of oxidizing materials, enhance the degradation efficiency of target pollutants. Herein, we report an easy-synthesis of ZIF67@C3N4 and MIL-100(Fe)@C3N4 by in-situ hydrothermal growth route for the photocatalytic degradation of perfluorooctanoic acid (PFOA). Unlike bare g-C3N4, ZIF67@C3N4 and MIL-100(Fe)@C3N4 composites exhibit higher specific surface areas which enhanced the adsorption properties. Moreover, the formed heterojunction systems boost the visible light responsive and the separation of photo-induced electrons, allowing excellent degradation of PFOA. Besides the same response to spectrum below 420 nm as C3N4, ZIF67@C3N4 holds a certain light absorption capacity between 500 and 600 nm, proving that ZIF67@C3N4-X has better light utilization capacity than ZIF67 and C3N4. With the increase of MIL-100(Fe) addition, the red-shift becomes significant. Through the preliminary photocatalytic tests using methylene blue as a representative organic pollutant, the results showed that ZIF67@C3N4-24.4% and MIL-100(Fe)@C3N4-70% are the most effective. When ZIF67@C3N4-24.4% and MIL-100(Fe)@C3N4-70% were applied comparatively towards the photocatalytic oxidation of PFOA, the results showed that the removal rates reached 79.2% and 60.5%, respectively, which is much higher than bare C3N4. The quenching tests indicated that photo-induced h+ played a major role in the photocatalytic degradation of PFOA by ZIF67@C3N4-24.4%, while O2- and h+ participated equality towards the PFOA degradation in MIL-100(Fe)@C3N4-70% system. Besides the photonic effects, it was suggested that the adsorption and electron shuttle effect also played significant role on the excellent removal of PFOA, wherein the adsorption e behavior of catalysts help the accumulation of PFOA nearby the photoactive C3N4 area. In addition, this process promoted further mineralization of generated intermediate products, making the system more sustainable.

Development of a new photoelectrochemical system for clean hydrogen production and a comparative environmental impact assessment with other production methods

Hydrogen is recognized as a critical substance for diversifying the global energy supply, providing new economic opportunities and realizing a carbon-free energy sector. In the current study, a life cycle assessment is conducted on a photoelectrochemical hydrogen production process of a newly developed photoelectrochemical reactor. With a photoactive electrode area of 870 cm2, the hydrogen production rate of the reactor is 47.1 μg/s while operating with the energy and exergy efficiencies of 6.3% and 6.31%, respectively. For a Faradaic efficiency of 96%, the produced current density is evaluated as 3.15 mA/cm2. A comprehensive study is conducted for a cradle-to-gate life cycle assessment of the proposed hydrogen photoelectrochemical production system. The life cycle assessment results of the proposed photoelectrochemical system are further evaluated within a comparative analysis by considering a total of four key hydrogen generation processes, namely steam-methane reforming, photovoltaics-based and wind electricity-driven proton exchange membrane water electrolysis and the current photoelectrochemical system and studying five environmental impact categories. The global warming potential of hydrogen production via the proposed photoelectrochemical cell is evaluated as 1.052 kg CO2 equivalent per kg of produced hydrogen. In the normalized comparative life cycle assessment results, the PEC-based hydrogen production is found to be the most nature-friendly option among the considered pathways.

Bi2O2Se Nanowire/MoSe2 Mixed-Dimensional Polarization-Sensitive Photodiode with a Nanoscale Ultrafast-Response Channel.

In recent years, polarization-sensitive photodiodes based on one-dimensional/two-dimensional (1D/2D) van der Waals (vdWs) heterostructures have garnered significant attention due to the high specific surface area, strong orientation degree of 1D structures, and large photo-active area and mechanical flexibility of 2D structures. Therefore, they are applicable in wearable electronics, electrical-driven lasers, image sensing, optical communication, optical switches, etc. Herein, 1D Bi2O2Se nanowires have been successfully synthesized via chemical vapor deposition. Impressively, the strongest Raman vibration modes can be achieved along the short edge (y-axis) of Bi2O2Se nanowires with high crystalline quality, which originate from Se and Bi vacancies. Moreover, the Bi2O2Se/MoSe2 photodiode designed with type-II band alignment demonstrates a high rectification ratio of 103. Intuitively, the photocurrent peaks are mainly distributed in the overlapped region under the self-powered mode and reverse bias, within the wavelength range of 400-nm. The resulting device exhibits excellent optoelectrical performances, including high responsivities (R) and fast response speed of 656 mA/W and 350/380 μs (zero bias) and 17.17 A/W and 100/110 μs (-1 V) under 635 nm illumination, surpassing the majority of reported mixed-dimensional photodiodes. The most significant feature of our photodiode is its highest photocurrent anisotropic ratio of ∼2.2 (-0.8 V) along the long side (x-axis) of Bi2O2Se nanowires under 635 nm illumination. The above results reveal a robust and distinctive correlation between structural defects and polarized orientation for 1D Bi2O2Se nanowires. Furthermore, 1D Bi2O2Se nanowires appear to be a great potential candidate for high-performance rectifiers, polarization-sensitive photodiodes, and phototransistors based on mixed vdWs heterostructures.

A newly developed experimental green hydrogen generator: Analysis and assessment

• A new hydrogen production cell with a unique photoelectrode geometry is investigated. • Both energetic and exergetic analyses of the PEC cell unit are conducted. • An electrochemical modelling of the PEC cell is performed. • Hydrogen production as 47.1 μg/s with an STH efficiency of 5.94% from the PEC cell. Photoelectrochemical (PEC) cells are recognized as promising devices for clean hydrogen production from free and abundant sources of solar energy and water only. This study investigates a new PEC cell possessing a unique electrode geometry to maximize the photoactive electrode surface area and hence the process efficiency. This conic-mesh structural design of the working electrode provides a passive solar-light tracking characteristic to the system enhancing the solar light absorption throughout daylight time. The performance of the PEC-based hydrogen production is evaluated through thermodynamic and electrochemical analyses and assessments. The effects of numerous critical design and operational parameters, including solar irradiance intensity, quantum efficiency, illuminated electrode area and generated current density, on the performance of the PEC cell are investigated by the parametric studies conducted. Using the current PEC generator, hydrogen is produced at a rate of 47.1 μg/s operating with an solar to hydrogen (STH) efficiency of 5.94% that occurs at a 20% quantum efficiency under 600 W/m 2 of solar irradiance intensity. With an applied bias of 1.5 V producing the current density of 2.29 mA/cm 2 at the presence of solar light, both energetic and exergetic efficiencies of the PEC generator are found to be 6.30% and 6.38%, respectively.

Hairy Conjugated Microporous Polymer Nanoparticles Facilitate Heterogeneous Photoredox Catalysis with Solvent-Specific Dispersibility.

Substrate accessibility is a key limiting factor for the efficiency of heterogeneous photoredox catalysis. Recently, a high photoactive surface area of conjugated microporous polymer nanoparticles (CMP NPs) has made them promising candidates for overcoming the mass transfer limitation to achieve high photocatalytic efficiency. However, this potential has not been realized due to limited dispersibility of CMP NPs in many solvents, particularly in water. Here, we report a polymer grafting strategy that furnishes versatile hairy CMP NPs with enhanced solvent-specific dispersibility. The method associates hundreds of solvent-miscible repeating units with one chain end of the photocatalyst surface, allowing minimal modification to the CMP network that preserves its photocatalytic activity. Therefore, the enhanced dispersibility of hairy CMP NPs in organic solvents or aqueous solutions affords high efficiency in various photocatalytic organic transformations.

Nanosized titanium dioxide particle emission potential from a commercial indoor air purifier photocatalytic surface: A case study.

Background: Photocatalytic air purifiers based on nano-titanium dioxide (TiO 2) visible light activation provide an efficient solution for removing and degrading contaminants in air. The potential detachment of TiO 2 particles from the air purifier to indoor air could cause a safety concern. A TiO 2 release potential was measured for one commercially available photocatalytic air purifier "Gearbox Wivactive" to ensure a successful implementation of the photocatalytic air purifying technology. Methods: In this study, the TiO 2 release was studied under laboratory-simulated conditions from a Gearbox Wivactive consisting of ceramic honeycombs coated with photocatalytic nitrogen doped TiO 2 particles. The TiO 2 particle release factor was measured in scalable units according to the photoactive surface area and volume flow (TiO 2-ng/m 2×m 3). The impact of Gearbox Wivactive on indoor concentration level under reasonable worst-case conditions was predicted by using the release factor and a well-mixed indoor aerosol model. Results: The instrumentation and experimental setup was not sufficiently sensitive to quantify the emissions from the photoactive surfaces. The upper limit for TiO 2 mass release was <185×10 -3 TiO 2-ng/m 2×m 3. Under realistic conditions the TiO 2 concentration level in a 20 m 3 room ventilated at rate of 0.5 1/h and containing two Gearbox Wivactive units resulted <20×10 -3 TiO 2-ng/m 3. Conclusions: The release potential was quantified for a photocatalytic surface in generalized units that can be used to calculate the emission potential for different photocatalytic surfaces used in various operational conditions. This study shows that the TiO 2 nanoparticle release potential was low in this case and the release does not cause relevant exposure as compared to proposed occupational exposure limit values for nanosized TiO 2. The TiO 2 release risk was adequately controlled under reasonable worst-case operational conditions.

Li-Doped ZnO Electron Transport Layer for Improved Performance and Photostability of Organic Solar Cells.

Organic solar cells (OSCs) based on an inverted architecture generally have better stability compared to those based on a standard architecture. However, the photoactive area of the inverted solar cells increases under ultraviolet (UV) or solar illuminatiom because of the too-high conductivity of the UV-illuminated zinc oxide (ZnO) interlayer. This limits the potential of the inverted solar cells for industrial applications. Herein, lithium-doped ZnO (Li-ZnO) films are employed as the cathode interlayer to construct inverted OSCs. The incorporation of Li ions is found to reduce the lateral conductivity of the UV-treated ZnO films because of the presence of Li ions, preventing the high-quality-growth of ZnO nanocrystals. This addresses the problem of having too-high conductivity in the UV-treated ZnO layer, causing the increased photoactive area of inverted solar cells. The overall performance of the solar cell is shown to be higher after the incorporation of Li ions in the ZnO layer, mainly due to the increased fill factor (FF), originating from the reduced trap-assisted recombination losses. Finally, the inverted solar cells based on the Li-ZnO interlayer are demonstrated to have a much better long-term stability, as compared to those based on ZnO. This allows the ZnO-based interlayers to be used for the mass production of organic solar cell modules.

White-light photodetection enhancement and thin film impediment in Bi2S3 nanorods/thin-films homojunction photodetectors

The arrays of one-dimensional (1D) nanorods and thin films of Bi2S3 are synthesized using the hot-plate thermal vapor deposition technique. The controlled synthesis forms the homojunction of thin films of varying thicknesses and 1D nanorods and possesses stoichiometric orthorhombic crystal structures. The same chemical and crystalline composition with different morphological features offer to study the effects of homojunction and dimensions on the performances of the homojunction white-light Bi2S3 photodetectors. The responsivity and detectivity of the vertically standing arrays of 1D nanorods and ultrathin thin films of Bi2S3@15 photodetectors are obtained to be ∼749.3 mA/W and ~5.61 × 108 Jones, respectively. The response times of the Bi2S3 photodetectors to be very short of 162 ms. The study of varying thicknesses of the thin films shows that the larger thickness of thin films impedes the performances of Bi2S3 photodetectors. Also, the larger photo-active area provided by the arrays of nanorods enhances the photodetection in nanorods/thin films homojunction Bi2S3 photodetectors.

Accelerated Proton Transport Based on a p-i-n Heterostructure Membrane for Low-Temperature Solid Oxide Fuel Cells

The p-i-n junction structure has garnered great interest from researchers due to its increased photoactive area and wider space charger region compared with that of the p-n junction. Herein the ult...

Nanoscale water spray assisted synthesis of CAs@B-TiO2 core–shell nanospheres with enhanced visible-light photocatalytic activity

Increasing photoactive areas and oxygen vacancy to improve the separation and utilization of electrons and holes in a photocatalytic process are a guarantee for highly photocatalysis efficiency. In this work, we report a CAs@B-TiO2 core–shell nanospheres via a nanoscale water spray assisted method to deposit of black titanium dioxide (B-TiO2) on carbon aerogel sphere (CAs) though slowly hydrolyzing of butyl titanate (e.g. TBOT) in an ethanol-water system. On this basis, furthermore, a facile one-step N2H4 · H2O treatment was used to introduces oxygen vacancies on the surface of TiO2 coating layer forming black TiO2. Oxygen vacancies can extend the optical response range of the TiO2 shell from the ultraviolet to the visible region, and increase conductivity and charge transport on the interface of core–shell structure. This study reveals the importance of surface oxygen vacancies for reducing band gaps and developing highly active photocatalysts under visible light.

An underestimated photoactive area in organic solar cells based on a ZnO interlayer

UV-induced doping reduces the resistance of the ZnO interlayer in an organic solar cell, leading to an increased photoactive area. This results in a significantly overestimated Jsc in the solar cell characterized without using a mask.

NOx depolluting performance of photocatalytic materials in an urban area - Part II: Assessment through Computational Fluid Dynamics simulations

Photocatalytic materials are proposed as a mitigation strategy of urban air pollution because of its deposition feature. This study aims at evaluating their effect on NO2 concentrations in an urban environment under real atmospheric conditions through Computational Fluid Dynamics (CFD) simulations. A comprehensive study is performed to determine the potential of photocatalytic materials to remove NO2 at pedestrian level taking into account the variability of wind speed, traffic emissions and the photoactive area in an urban environment. The deposition velocity used to model the sink effect of a photoactive surface is derived from laboratory data and its applicability to outdoor conditions is proved through microscale simulations. The CFD simulation performed to assess the impact of a photocatalytic material on ambient pollutants in a real urban scenario is evaluated against the measurements presented in Part I (Fernández-Pampillón et al., 2020). Results show that the application of photocatalytic materials in an urban environment yield a minimal reduction in NO2 concentrations below 1% under the studied atmospheric conditions. In a hypothetical scenario, in which the photoactive area is extended to an entire neighbourhood, small decrease of NO2 concentrations below 2% is obtained under the daytime prevailing atmospheric conditions of the area of interest. Finally, the reduction of NO2 under several atmospheric conditions results to be mainly dominated by wind flow and NOx emissions in the study street.

Chemical passivation of the perovskite layer and its real-time effect on the device performance in back-contact perovskite solar cells

The back-contact architecture for perovskite solar cells (PSCs) offers the possibility of positioning both electrodes on one side of the absorber layer and shining light directly on the perovskite photoactive layer. This helps us to avoid the occurrence of transmission losses caused by the charge collecting transparent conductive oxide electrode in the conventional sandwich structure for PSCs. The back-contact device architecture is also useful for conducting fundamental studies as it has an exposed photoactive area, permitting in situ measurements on the effects of chemical treatment, passivation, and annealing. A successful application of back-contact PSCs in studying the effect of chemical passivation of the perovskite photo-absorber layer trap states with pyridine and its influence on the device performance have been studied. The real-time effect of pyridine vapor treatment on the device performance is visualized by monitoring the maximum power output of the devices under operation conditions. The device performance enhancement by ∼12% owing to the surface passivating effect of pyridine is demonstrated.

Digging Deeper for an In-Depth Understanding of Energy Materials

Oftentimes, advanced microscopy studies that measure the local performance of energy materials are restricted to probing the surface. Yet, it is recognized that critical operational processes occur within these devices. In Nature Communications, Song et al. dig deeper by implementing tomographic atomic force microscopy to study local electrical transport pathways in a thin-film halide perovskite. From this yields a 3D, nanoscale spatial resolution map of the photoactive area, demonstrating how visualizing material interiors expands our understanding of next-generation energy devices.

A Beehive Inspired Hydrogen Photocatalytic Device Integrating a Carbo‐Benzene Triptych Material for Efficient Solar Photo‐Reduction of Seawater

AbstractThe dream to produce green, clean, and sustainable hydrogen from earth‐abundant and free resources such as seawater and sunlight is highly motivating because of the interest for desirable economical and societal applications in energy. However, it remains challenging to develop an efficient and unassisted photocatalytic device to split seawater molecules with just sunlight without any external bias. For the first time, a such novel hierarchical material has been developed, based on thin film technology that integrates TiO2 semiconductor layers, embedded gold nanoparticles, and a photosensitive carbo‐benzene layer. The design of the triptych device placing the photocatalyst in be‐to‐be increases the photoactive surface area by a factor 2. Its stability (&gt;120 successive hours of hydrogen production and &gt;5 days in a day/night representative alternation) and efficiency (Soler‐to‐Hydrogen 0.06%) are measured in NaCl‐salted water. The chloride ions act as hole scavengers and induce an increase of pH increasing in turn the sun‐driven hydrogen production rate.

Designing a new data acquisition circuit for SiPM-based detection systems—MexSiC

Silicon Photomultipliers (SiPM) are currently an excellent option to replace the traditional photomultiplier tubes (PMT) due to the fact that they require much lower operational voltages than the PMTs with photon detection efficiencies (PDE) higher than 40% at peak wavelengths (in the blue-green visible part of the spectra), do not require the electromechanical complexity related with PMT based solutions, and are insensitive to magnetic fields. However, one disadvantage of SiPMs, if used in applications where huge detection areas are required, is their respectively small photoactive area (of few square millimeters). Modular approaches based on arrays of SiPMs are normally used in such cases. In order to use SiPM arrays, the modular data acquisition (DAQ) systems must be capable of reading multiple channels in parallel, synchronizing the times of arrival of all SiPM output pulses, processing these pulses, discriminating between events, and generating resulting digital output signals that can be stored on an external memory unit. An application specific integrated circuit (MexSIC) to be fabricated in the 180 nm CMOS technology has been designed as a core unit of such a DAQ system. It contains a transimpedance amplifier (TIA) as its input stage, a triggering logic unit (TLU) used to discriminate the input signals, a phase locked loop (PLL) used to generate a clock reference for the time-to-digital converter (TDC) and an additional charge-to-digital converter (QDC), used for discrimination of detected events based on the amount of charge generated within each individual SiPM on the one side, and the duration of each event on the other, as well as a Delta-Sigma (Δ-Σ) analog-to-digital converter (ADC). An additional field-programmable gate array (FPGA), the Xilinx Kintex 7, is used for signal processing and system controlling. We present the concept of the proposed DAQ system.