High Power Conversion Efficiency Research Articles

Design and Implementation of GaN-Based Two Switch Flyback With Synchronous Rectification for New Space Applications

This article presents a comprehensive investigation and implementation of a continuous conduction mode pulse width modulated two-switch DC/DC flyback converter utilizing Gallium Nitride Field Effect Transistors (GaNFETs) for New Space applications. The New Space concept advocates for the integration of Commercial Off-The-Shelf (COTS) materials in the space industry. The approach offers cost-effective solutions and reduces lead time for space designs. The study provides steady-state analysis and design considerations for two switch flyback converters, highlighting the transformative capabilities of GaNFETs, especially in high-frequency operations. The rationale behind the preference for GaNFETs over MOSFETs in satellite power supply applications and the strategic benefits of COTS materials are explained in detail. In addition, the synchronous rectification method is implemented to obtain better efficiency, particularly for high-output current operations. The converter achieves an efficiency of over 87% when the load exceeds 50%, with varying input voltages from 20 V to 40 V and a switching frequency of 300 kHz. The experimental findings show that the designed converter can serve as a high efficiency and reliable satellite power converter.

Underwater Power Conversion and Junction Technology for Underwater Wireless Power Transfer Stations

Underwater wireless power transfer (UWPT) systems are appropriate for battery charging of compact, submerged devices without a complicated and expensive sealing structure or human contact because the power source and load are not physically connected. For the shore-based power supply situation, the underwater power conversion and junction technology should be required to drop down shore-based voltage to the target voltage for the underwater energy supply of the UWPT system. This paper proposes a lightweight, high efficiency and power density underwater power conversion connector system for the UWPT system, in which the LLC resonant converter is constructed with SiC transistors. The full load range zero-voltage switching (ZVS) and load adaptive characteristics have been achieved. The optimized RC level shift driver is adopted to highly reduce the switching loss of SiC transistors. Shore-based voltage of 1000 V was converted to the target voltage of 375 V for the UWPT system. The highest measured efficiency is over 98% at a load power level of 1500 W underwater conditions.

High-performance intrinsically stretchable organic solar cells based on flexible spacer incorporated dimerized small-molecule acceptors

High power conversion efficiency (PCE), long-term stability, and mechanical robustness are important requirements for the practical applications of organic solar cells (OSCs). Herein, we develop a series of flexible spacer (FS)-incorporated dimerized small-molecule acceptors (DSMAs; DYBT-C0, DYBT-C4, and DYBT-C8) and demonstrate high-performance OSCs with a high PCE of 18.6%, excellent mechanical robustness (crack-onset strain (COS) = 32%) and photostability (t80% lifetime = 1735 h under 1-sun illumination). The incorporation of aliphatic FS units with optimal length effectively reduces the backbone rigidity of the DSMAs and increases the fraction of intermixed domains in the blend films, while maintaining excellent electron transport properties. The DYBT-C4-based OSCs demonstrate higher PCE (18.6%) and stretchability (COS = 32%) compared to the OSCs based on the monomer acceptor (MYT; PCE = 15.9% and COS = 10%) and DSMA without FS units (DYBT-C0; PCE =17.2% and COS = 17%). In addition, due to the reduced diffusion coefficient and higher glass transition temperature of DYBT-C4, the DYBT-C4-based OSCs exhibit photostability significantly higher than that of the OSCs fabricated using MYT (t80% lifetime= 36 h). Consequently, DYBT-C4-based intrinsically stretchable (IS)-OSCs exhibit high device stretchability (strain at PCE80% = 36%) and PCE of 14.3%, demonstrating potential for wearable applications.

Synergetic optimizing quinoxaline and selenophene substitution in non-fullerene acceptors for efficient organic solar cells

Selenophene-fused non-fullerene acceptors (Se-NFAs) usually exhibited improved short circuit current density (JSC) in organic solar cells, while acceptors bearing quinoxaline (Qx) unit as the central core could achieve enhanced open circuit voltage (VOC). Herein, we incorporated the advantages of the above two strategies and synthesized four nonfullerene acceptors (Qx-Se-NFAs), including Qx-Se-F, Qx-Se-Cl, p-2FQx-Se-F, and p-2FQx-Se-Cl. Compared with CH1007 (the symmetrical selenium analog of Y6), the four acceptors-based devices showed evidently improved VOC and fill factor (FF) with well-maintained JSC, achieving excellent power conversion efficiency (PCE). Qx-Se-NFAs-based devices with the fluorinated terminal group exhibit evidently advantages on VOC and FF compared with the chlorinated terminal group due to the up-shifted LUMO energy level and optimized blend film. In addition, the acceptors with fluorination on the central core could further endow device with improved carrier properties and film morphology. Consequently, the device based on Qx-Se-F exhibited the highest VOC of 0.867 V among the reported PM6:Se-NFA systems. The p-2FQx-Se-F-based device yielded a champion PCE of 18.67% by using 2PACz as the hole transport layer, which is the highest PCE in the reported Se-NFAs among the single-junction binary OSCs. This work demonstrated a promising strategy that could better trade-off JSC, FF, and VOC in Se-NFAs.

A Quantitative Analysis of the Need for High Conversion Efficiency PV Technologies in Carbon Mitigation Strategies

We consider the restrictions on photovoltaic (PV) capacity that are caused by limitations on where panels can be sited and find quantitative evidence for the need for high efficiencies. We define 15% of the UK’s energy consumption as a “significant” contribution and, with London as an exemplar, we perform an idealised calculation that makes the most optimistic possible assumptions about the capabilities of future PV technologies and use published surveys on energy usage, dwelling type and insolation. We find that covering every UK domestic roof with the highest power conversion efficiency (PCE) solar panels currently commercially available could produce up to 9% of the UK’s energy. A 15% contribution would require PV technologies with >37% PCE, more than the theoretical Shockley–Queisser limit. Replacing the idealising assumptions with more realistic estimates increases this by 2–3 times. Alternatively, a solar farm using the currently available PCEs would require a politically challenging ~1200 km2 of new land, roughly the area of Greater London, for this 15% contribution. We conclude that PCEs must be driven higher than even the Shockley–Queisser limit for PV to play a significant part in carbon mitigation.

Highly efficient self-powered CH3NH3Pbl3 perovskite photodiode with double-sided poly(methyl methacrylate) passivation layers

Hybrid organohalide perovskites have recently attracted significant attention due to their outstanding photovoltaic (PV) conversion capabilities in optoelectronic devices. Herein, to develop a highly sensitive and self-powered perovskite-based PV photodiode (PVPD), we implement the selective use of poly(methyl methacrylate) (PMMA) as noise-current-reducing passivation layers on both the front and rear sides of a CH3NH3PbI3 (MAPbI3) perovskite light-absorbing layer. It is found that the PMMA layers effectively suppress carrier recombinations at the interfaces, resulting in fairly high power conversion efficiency of 17.6%. Additionally, the double-sided PMMA-passivated MAPbI3 PVPD shows exceptional specific detectivity values (1.0 × 1014 Jones from the dark current and 1.3 × 1012 Jones from the noise current), significantly outperforming conventional MAPbI3 PVPDs without passivation layers. The device also exhibits a very wide linear dynamic response range of ∼139 dB, with rapid rise and decay response times of 57 and 18 μs, respectively. The double-sided PMMA-passivated MAPbI3 PVPD also is shown to be highly durable in terms of its dynamic responses even after a prolonged storage period of 1500 h. These results suggest that advanced interface engineering using double PMMA passivation layers holds great potential for developing high-performance self-powered perovskite photodetectors for a range of optoelectronic applications.

Vanadyl Sulfate Based Hole‐Transporting Layer Enables Efficient Organic Solar Cells

Comprehensive SummaryIt remains an urgent task to develop alternative hole‐transporting layer (HTL) materials beyond commonly used PEDOT:PSS to increase the shelf‐life of organic solar cells (OSCs). Inorganic metal oxide type materials, such as NiOx, CoOx and VOx, with suitable work functions have attracted numerous research attention recently. In this work, more abundant and easily accessible oxygenated salt, vanadyl sulfate (VOSO4) has been demonstrated to be excellent choice as HTL for OSCs. The VOSO4‐based HTL can be readily processed by spin‐coating from the precursor solution with subsequent thermal annealing and UVO treatment. As a consequence, a high power conversion efficiency (PCE) of 18.72% can be achieved for PM8:L8‐BO based OSCs with the VOSO4‐based HTL. High transmittance, smooth film surface, suitable energy level and high conductivity were revealed to contribute to the high OSC performance. More importantly, compared to device with PEDOT:PSS, VOSO4‐based OSCs exhibit improved stability when stored in the N2 filled glove box. After being stored for 600 h, VOSO4‐based device can retain 89% of its initial efficiency. Notably, VOSO4 can be used as general HTL in PM6:BTP‐BO‐4Cl and PM6:IT‐4F based OSCs, yielding high PCEs of 17.87% and 13.85%, respectively.

Efficient Ternary Organic Solar Cells with Suppressed Nonradiative Recombination and Fine-Tuned Morphology via IT-4F as Guest Acceptor.

The large open circuit voltage (VOC) loss is currently one of the main obstacles to achieving efficient organic solar cells (OSCs). In this study, the ternary OSCs comprising PM6:BTP-eC9:IT-4F demonstrate a superior efficiency of 18.2 %. Notably, the utilization of the medium bandgap acceptor IT-4F as the third component results in an exceptionally low nonradiative recombination energy loss of 0.28 V. The desirable energy level cascade is formed among PM6, BTP-eC9, and IT-4F due to the low-lying HOMO and LUMO energy levels of IT-4F. More importantly, the VOC of PM6:BTP-eC9:IT-4F OSCs can reach as high as 0.86 V, which is higher than both binary OSCs without sacrificing JSC and FF. Besides, this strategy proved that IT-4F can not only broaden the absorption range but also work as a morphology modifier in PM6:BTP-eC9:IT-4F OSCs, and there also exists efficient energy transfer between BTP-eC9 and IT-4F. This result provides a promising way to suppress the nonradiative recombination energy loss and realize higher VOC than the two binary OSCs in ternary OSCs to obtain high power conversion efficiencies.

Transparent low moisture permeable coating for perovskite solar cell encapsulation

The perovskite solar cell has potential to become next generation photovoltaics due to its high power conversion efficiency and easy processing. However, the perovskite solar cell is very sensitive to moisture and temperature which needs to be protected by low temperature processable moisture permeation coating. Furthermore, the encapsulating coating has to be transparent so the perovskite solar cell can be kept its transparency and used in integrated building structure or tandem with Si solar cell, etc. The coating material should be solventless which will not damage the perovskite layer and release any harmful volatile organic compounds during the coating application process. A solventless hybrid coating made from polyfluoroesterimide and silica nanoparticle has been developed which can be cured within minutes using mercury lamp (light intensity 935 W/m2) at room temperature. The coating exhibits low moisture permeation and high transparency. The performance improvement is due to the presence of water repelling characteristic of fluoro moiety and less moisture permeable inorganic silica component. The encapsulated devices exhibit long-term stability when they were subjected to the environment of 65 °C and 65%RH for >400 h.

Completely annealing-free flexible Perovskite quantum dot solar cells employing UV-sintered Ga-doped SnO2 electron transport layers

The electron transport layer (ETL) is a critical component in perovskite quantum dot (PQD) solar cells, significantly impacting their photovoltaic performance and stability. Low-temperature ETL deposition methods are especially desirable for fabricating flexible solar cells on polymer substrates. Herein, we propose a room-temperature-processed tin oxide (SnO2) ETL preparation method for flexible PQD solar cells. The process involves synthesizing highly crystalline SnO2 nanocrystals stabilized with organic ligands, spin-coating their dispersion, followed by UV irradiation. The energy level of SnO2 is controlled by doping gallium ions to reduce the energy level mismatch with the PQD. The proposed ETL-based CsPbI3-PQD solar cell achieves a power conversion efficiency (PCE) of 12.70%, the highest PCE among reported flexible quantum dot solar cells, maintaining 94% of the initial PCE after 500 bending tests. Consequently, we demonstrate that a systemically designed ETL enhances the photovoltaic performance and mechanical stability of flexible optoelectronic devices.

Stability enhancement of perovskite solar cells using multifunctional inorganic materials with UV protective, self cleaning, and high wear resistance properties

Organometal halide perovskite solar cells have reached a high power conversion efficiency of up to 25.8% but suffered from poor long-term stability against environmental factors such as ultraviolet irradiation and humidity of the environment. Herein, two different multifunctional transparent coatings containing AZO and ZnO porous UV light absorbers were employed on the front of the PSCs. This strategy is designed to improve the long-term stability of PSCs against UV irradiation. Moreover, the provided coatings exhibit two additional roles, including self-cleaning and high wear resistance. In this regard, AZO coating showed higher wear resistance compared to the ZnO coating. The photocatalytic self-cleaning properties of these prepared coatings make them stable against environmental pollutants. Furthermore, appropriate mechanical properties such as high hardness and low coefficient of friction that leads to high resistance against wear are other features of these coatings. The devices with AZO/Glass/FTO/meso-TiO2/Perovskite/spiro/Au and ZnO/Glass/FTO/meso-TiO2/Perovskite/spiro/Au configurations maintained 40% and 30% of their initial performance for 100 h during 11 days (9 h per day) against the UV light with the high intensity of 50 mW cm-2 which is due to higher absorption of AZO compared with ZnO in the ultraviolet region. Since AZO has a higher light transmission in the visible region in comparison to ZnO, perovskite cells with AZO protective layers have higher efficiency than perovskite cells with ZnO layers. It is worth noting that the mentioned features make these coatings usable for cover glass in all types of solar cells.

Strategies for Improving Efficiency and Stability of Inverted Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted widespread research and commercialization attention because of their high power conversion efficiency (PCE) and low fabrication cost. The long-term stability of PSCs should satisfy industrial requirements for photovoltaic devices. Inverted PSCs with a p-i-n architecture exhibit considerable advantages because of their excellent stability and competitive efficiency. The continuously broken-through PCE of inverted PSCs shows huge application potential. This review summarizes the developments and outlines the characteristics of inverted PSCs including charge transport layers (CTLs), perovskite compositions, and interfacial regulation strategies. The latest effective CTLs, interfacial modification, and stability promotion strategies especially under light, thermal, and bias conditions are emphatically analyzed. Furthermore, the applications of the inverted structure in high-efficiency and stable tandem, flexible photovoltaic devices, and modules and their main obstacles are systematically introduced. Finally, the remaining challenges faced by inverted devices are discussed, and several directions for advancing inverted PSCs are proposed according to their development status and industrialization requirements.

Healing the Buried Interface by a Plant-Derived Green Passivator for Carbon-Based CsPbIBr2 Perovskite Solar Cells.

Perovskite solar cells (PSCs) have attracted extensive attention in photovoltaic applications owing to their superior efficiency, and the buried interface plays a significant role in determining the efficiency and stability of PSCs. Herein, a plant-derived small molecule, ergothioneine (ET), is adopted to heal the defective buried interface of CsPbIBr2-based PSC to improve power conversion efficiency (PCE). Because of the strong interaction between Lewis base groups (-C═O and -C═S) in ET and uncoordinated Pb2+ in the perovskite film from the theoretical simulations and experimental results, the defect density of the CsPbIBr2 perovskite film is significantly reduced, and therefore, the nonradiative recombination in the corresponding device is simultaneously suppressed. Consequently, the target device achieves a high PCE of 11.13% with an open-circuit voltage (VOC) of 1.325 V for hole-free, carbon-based CsPbIBr2 PSCs and 14.56% with a VOC of 1.308 V for CsPbI2Br PSCs. Furthermore, because of the increased ion migration energy, the detrimental phase segregation in this mixed-halide perovskite is weakened, delivering excellent long-term stability for the unencapsulated device in ambient conditions over 70 days with a 96% retention rate of initial efficiency.

Guidelines for Material Design in Semitransparent Organic Solar Cells

AbstractOrganic solar cells (OSCs) are uniquely suited for semitransparent applications due to their adjustable absorption spectrum. However, most high‐performance semitransparent cells reported to date are based on materials that have shown high power conversion efficiency for opaque devices. A model is therefore presented to assess the optimum efficiency and transparency for a specific donor and acceptor bandgap. The absorption characteristics of both donor and acceptor are modeled with spectral data of typical absorber materials from the literature which are adjusted to achieve the desired bandgap value. The results show three distinct regions of high light utilization efficiency (LUE) if the photopic curve is employed as a weighting function (corresponding to window applications), and a broad maximum for the plant action spectrum as a weighting function (corresponding to greenhouse applications). When comparing these findings to reported experimental values, it is evident that the bandgaps of the materials used for the experimental studies do not correspond to the maxima identified by the simulation model. The analysis of the energy levels of molecules recorded in the literature confirms that all bandgaps and therefore all LUE maxima are chemically feasible so that the performance of semitransparent OSCs can be further improved by designing materials with optimized absorption spectra.

Cost-Effective Cathode Interlayer Material for Scalable Organic Photovoltaic Cells.

Organic photovoltaic (OPV) cells have demonstrated remarkable success on the laboratory scale. However, the lack of cathode interlayer materials for large-scale production still limits their practical application. Here, we rationally designed and synthesized a cathode interlayer, named NDI-Ph. Benefiting from their well-modulated work function and self-doping effect, NDI-Ph-based binary OPV cells achieve an excellent power conversion efficiency (PCE) of 19.1%. NDI-Ph can be easily synthesized on a 100 g scale with a low cost of 1.96 $ g-1 using low-cost raw materials and a simple postprocessing method. In addition, the insensitivity to the film thickness of NDI-Ph enables it to maintain a high PCE at various coating speeds and solution concentrations, demonstrating excellent adaptability for high-throughput OPV cell manufacturing. As a result, a module with 21.9 cm2 active area achieves a remarkable PCEactive of 15.8%, underscoring the prospects of NDI-Ph in the large-scale production of OPV cells.

High-Efficiency Reconfigurable CMOS RF-to-DC Converter System for Ultra-Low-Power Wireless Sensor Nodes with Efficient MPPT Circuitry

This paper presents a novel CMOS RF-to-DC converter for ultra-low-power wireless sensor nodes powered by RF wireless power transfer. The proposed converter achieves 10% higher power conversion efficiency than a conventional rectifier, with only a 1% increase in power consumption. The system employs a reconfigurable Dickson topology, operates on the unlicensed 868 MHz ISM band, and includes a built-in power-efficient MPPT system architecture. Experimental measurements show a maximum power conversion efficiency of 55% in the power range from −22 dBm to 0 dBm, with a power sensitivity of −22 dBm for a DC output voltage of 2.4 V. The proposed converter offers a promising solution for efficient wireless power transfer and energy harvesting in ultra-low-power wireless sensor nodes.

Suppressing Trap‐Assisted Nonradiative Recombination via Interface Modification for Achieving Efficient Organic Solar Cells

AbstractTrap states in organic solar cells (OSCs) can capture free charges, leading to a reduction in current density and significant energy loss. Since charge collection is primarily dependent on the interface layer, minimizing trap states at interfaces can effectively suppress energy losses, a topic that has been rarely explored. Herein, an interface strategy is proposed by combining Me‐4PACz and PEDOT:PSS to mitigate the trap‐assisted nonradiative recombination at the hole transport layer (HTL). OSCs based on the Me‐4PACz/PEDOT:PSS exhibit reduced trap densities and low energy losses compared to devices fabricated with a single‐layer HTL. This reduction can be attributed to a lower nonradiative recombination rate during hole transport at the interface. Changes in the work function of the two interlayers due to contact result in the existence of a built‐in potential inside the composite interlayer, promoting charge collection and reducing energy loss from charge recombination. Furthermore, the composite HTL interface induces vertical phase separation of active layer, leading to significant improvements of the fill factor for OSCs. As a result, high power conversion efficiencies (PCEs) of 18.70% and 19.02% are achieved for binary all‐polymer solar cells and polymer donor/small molecule acceptor solar cells, respectively.

Suppress energy loss to boost power conversion efficiency of organic photovoltaics with linear side chains modulation

The high energy loss (Eloss) in organic solar cells (OSCs) is being the one of major problem, which limit the power conversion efficiency (PCE) of OSCs. In this work, we designed and synthesized three perylene diimide (PDI)-based Acceptor’-Donor-Acceptor-Donor- Acceptor’ (A′-DAD-A′) small molecules namely anti-PDFC-Cx (C8, C10, and C12) by changing the length of linear chains on IDT cores to investigate how the length of linear side chain affects Eloss and the power conversion efficiencies (PCEs) of OSCs. The optical energy bandgap and stacking mode for three anti-PDFC-Cx (C8, C10, and C12) remain the same, which were not influenced by the different lengths of side chains. Increasing the length of side chains on IDT cores from C8 to C10 and C12 would improve the PCE of PM6: anti-PDFC-Cx based devices from 11.52% to 12.43% and 12.27%, particularly the Voc increasing from 0.98 V of anti-PDFC-C8 and 1.00 V of anti-PDFC-C10 to 1.02 V of anti-PDFC-C12. Eloss analysis indicated the value of Eloss reduced as the length increases from C8, to C12. These results demonstate linear side chain engineer is an effective method to reduce Eloss and realize high PCE on the bases of not modulating the stacking mode of acceptor.

Size-Controlled Cu3VSe4 Nanocrystals as Cathode Material in Platinum-Free Dye-Sensitized Solar Cells.

In this work, we report the first single-step, size-controlled synthesis of Cu3VSe4 cuboidal nanocrystals, with the longest dimension ranging from 9 to 36 nm, and their use in replacing the platinum counter electrode in dye-sensitized solar cells. Cu3VSe4, a ternary semiconductor from the class of sulvanites, is theoretically predicted to have good hole mobility, making it a promising candidate for charge transport in solar photovoltaic devices. The identity and crystalline purity of the Cu3VSe4 nanocrystals were validated by X-ray powder diffraction (XRD) and Raman spectroscopy. The particle size was determined from the XRD data using the Williamson-Hall equation and was found in agreement with the transmission electron microscopy imaging. Based on the electrochemical activity of the Cu3VSe4 nanocrystals, studied by cyclic voltammetry, the nanomaterials were further employed for fabricating counter electrodes (CEs) in Pt-free dye-sensitized solar cells. The counter electrodes were prepared from Cu3VSe4 nanocrystals as thin films, and the charge transfer kinetics were studied by electrochemical impedance spectroscopy. The work demonstrates that Cu3VSe4 counter electrodes successfully replace platinum in DSSCs. CEs fabricated with the Cu3VSe4 nanocrystals having an average particle size of 31.6 nm outperformed Pt, leading to DSSCs with the highest power conversion efficiency (5.93%) when compared with those fabricated with the Pt CE (5.85%).

Efficient Counter Electrode of MoS2‐GO/PEDOT:PSS for Platinum‐free, High Performance Dye Sensitized Solar Cells

AbstractThe aim of this work is to fabricate the efficient platinum‐free counter electrodes for the development of advanced and high performance dye sensitized solar cells. MoS2‐GO/ PEDOT:PSS counter electrode has served as low‐cost, simple preparation and high efficient counter electrode for a DSSC. The Cyclic‐Voltammetry, electrochemical impedance spectroscopy and Tafel curve analysis indicate that the MoS2‐GO/PEDOT:PSS counter electrode possesses low charge transfer resistance on the electrolyte–electrode interface, high electrocatalytic activity and fast reaction kinetics for the reduction of tri‐iodide to iodide at the counter electrode. The DSSCs made with MoS2‐GO/PEDOT:PSS counter electrode achieve high power conversion efficiency of 7.73 % under standard light illumination of 100 mW/cm2, is higher than the platinum based counter electrode DSSC (5.53 %). The results witnessed the developed counter electrode is efficient and potential for platinum‐free dye sensitized solar cell applications.