Enhanced Conversion Efficiency Research Articles

Advancing large-scale thin-film PPLN nonlinear photonics with segmented tunable micro-heaters

Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802% W−1 cm−2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device. The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification.

Nonradiative Energy Transfer Enables a hv < Eg Response of Perovskite Quantum Dots in Si-Based Inorganic-Organic Hybrid Solar Cells.

High performance is a crucial factor in seeking a more competitive levelized cost of electricity for the extensive popularization of c-Si solar cells. Here, CsPbBr3 quantum dots (QDs) have been first applied as the light-converting layer to enhance the full-spectrum light response, resulting in an ∼71% enhancement of power conversion efficiency within silicon-based solar cells. Remarkably, even if the photon energy is smaller than the bandgap of CsPbBr3 QDs, the long-wavelength external quantum efficiency shows a significant increase. Such surprising results can be attributed to the nonradiative energy transfer (NRET) mechanism of CsPbBr3 QDs, which can transfer long-wavelength-generated dipoles into the Si base with the assistance of a Coulomb force. Furthermore, a dipole-transferring model, which considers that the Al2O3 passivation layer would play a negative role in the NRET process, is creatively but supportively proposed. These results highlight a simple, low-cost but promising strategy to improve the performance of c-Si solar cells.

Target therapy at buried interfaces toward efficient and stable inorganic perovskite solar cells

The enhancement of power conversion efficiency (PCE) of perovskite solar cells (PSCs) is critically affected by charge recombination induced by buried interface defects. In light of this, a simple and effective target therapy strategy has been developed by doping 4-(diphenylphosphino)benzoic acid (4DBA) molecules at the tin oxide (SnO2)/perovskite interface. The effects of 4DBA on carrier transport, perovskite growth, defect passivation, and PSCs properties were systematically investigated. It is illustrated that 4DBA molecules not only passivate oxygen vacancy (OV) defects on the SnO2 surface, enhancing the conductivity of the SnO2 film and accelerating electron transfer, but also passivate perovskite interface defects, thereby improving the quality of the perovskite film. Ultimately, the efficiency of CsPbBr3 device with 4DBA-modified buried interface increased from 8.87% to 10.78%, an improvement of 21.53%. Furthermore, the efficiency of CsPbI2Br increased from 12.83% to 14.44%, an improvement of 12.55%, further demonstrating the effectiveness and universality of this strategy. Excitingly, the unencapsulated PSCs exhibit excellent long-term stability under high relative humidity and high temperatures.

Tuning Ce-doping La0.7Sr0.3Fe0.9Ni0.1O3-δ internal reforming catalyst to enhanced conversion efficiency and coking tolerance of solid oxide fuel cells fueled by oxygen-bearing low concentration coal mine methane

Solid oxide fuel cells (SOFCs) possess the potential to directly utilize abundant low concentration coal mine methane for power generation, which is crucial for energy conservation and reducing greenhouse gas emissions. Herein, Ce-doped La0.55Ce0.15Sr0.3Fe0.9Ni0.1O3-δ (LCSFN) perovskite is firstly employed as an anode internal reforming catalyst to enhance the electrochemical performance, stability, and resistance against carbon deposition in SOFCs. The results demonstrate that Ni-Fe alloy nanoparticles can be effectively precipitated from LCSFN under reducing atmosphere, thereby significantly promoting the partial oxidation reaction of methane while preventing direct contact between methane and Ni particles for the anode. The anode-supported single cells demonstrated exceptional electrochemical performance using a composite catalytic layer consisting of LCSFN-Ce0.9Gd0.1O2-δ (LCSFN-GDC). At 800℃, the utilization of both H2 and 16 %CH4-1 %O2-N2 resulted in the attainment of maximum power densities (MPD) measuring 881.66 mW·cm−2 and 824.69 mW·cm−2, respectively, with the recorded values for polarization resistance were 0.32 and 1.16 Ω·cm2. Additionally, the single cells equipped with LCSFN-GDC internal reforming catalytic exhibit remarkable resistance to carbon deposition, maintaining stable performance for a duration of 100 h using 16 %CH4-1 %O2-N2. These findings underscore the efficacy of methane catalysts in SOFCs, as it not only enhances power generation efficiency through using internal reforming catalyst but also ensures long-term stability by mitigating carbon-related issues.

Efficient wideband tunable radio frequency-optical conversion via triply resonant photonic molecules.

Electro-optic (EO) transduction of weak radio frequency (RF) and millimeter-wave signals, such as those received by an antenna, onto laser sidebands for processing in the optical domain requires efficient EO modulators. Microrings offer spatial density and efficiency advantages over Mach-Zehnder modulators (MZMs), but conventional single-ring modulators suffer a fundamental trade-off between resonantly enhanced conversion efficiency and the RF carrier frequency that it can accommodate. Dual-cavity "photonic molecule" modulators resolve this trade-off, allowing high efficiency independent of the RF carrier frequency by providing separate resonant supermodes to enhance the laser local oscillator (LO) and the narrowband RF-detuned sideband. However, the RF frequency is fixed at design time by geometry, with efficiency dropping quickly for RF carriers away from the design value. We propose a novel, to the best of our knowledge, triple-cavity configuration with an off-resonant middle ring acting as an effective tunable coupler between two active modulator cavities. This configuration provides wideband tunability of the target RF carrier while maintaining efficient sideband conversion. When the middle ring is passive (high Q), this configuration provides wide RF tunability with no efficiency penalty over the fixed dual-cavity case and could become an important building block for future RF/mm-wave photonic integrated circuits (PICs).

Stable colour conversion layer with enhanced conversion efficiency by incorporating nanoparticles for micro-LED display application

Due to their promising optical performance, micro-light emitting diodes (micro-LEDs) based on colour conversion layer (CCL) have garnered significant attention as the next-generation display technology. However, fabricating CCL with excellent conversion efficiency (CE) with minimal blue light leakage for miniaturized sub-pixel designing is still in its infancy. Herein, we have demonstrated CCL of a thickness (<3.5 μm) based on an organic-inorganic hybrid system incorporated with Titanium dioxide (TiO2) and Zinc Oxide (ZnO) Nanoparticles (NPs) with high CE. The inclusion of the NPs enhances the absorption of blue light within the CCL. We further combined the CCL with a colour purification filter to mitigate blue light leakage, which recycles blue light and suppresses blue light loss, resulting in improved CE. Specifically, we achieved a CE of 83.80 % for the green CCL and 66.97 % for the red CCL. Subsequently, full-colour arrays with a pixel size of 4 μm × 4 μm were successfully patterned and fabricated based on reduced thickness and improved optical performance using NP-doped CCL. This paves the way for cost-effective higher-resolution micro-LED displays for various applications.

Stable colour conversion layer with enhanced conversion efficiency by incorporating nanoparticles for micro-LED display application

Due to their promising optical performance, micro-light emitting diodes (micro-LEDs) based on colour conversion layer (CCL) have garnered significant attention as the next-generation display technology. However, fabricating CCL with excellent conversion efficiency (CE) with minimal blue light leakage for miniaturized sub-pixel designing is still in its infancy. Herein, we have demonstrated CCL of a thickness (<3.5 μm) based on an organic-inorganic hybrid system incorporated with Titanium dioxide (TiO2) and Zinc Oxide (ZnO) Nanoparticles (NPs) with high CE. The inclusion of the NPs enhances the absorption of blue light within the CCL. We further combined the CCL with a colour purification filter to mitigate blue light leakage, which recycles blue light and suppresses blue light loss, resulting in improved CE. Specifically, we achieved a CE of 83.80 % for the green CCL and 66.97 % for the red CCL. Subsequently, full-colour arrays with a pixel size of 4 μm × 4 μm were successfully patterned and fabricated based on reduced thickness and improved optical performance using NP-doped CCL. This paves the way for cost-effective higher-resolution micro-LED displays for various applications.

Systematic Engineering of Near-Infrared Small Molecules Based on 4H-Cyclopenta[1,2-b:5,4-b']dithiophene Acceptors for Organic Solar Cells.

Nonfullerene acceptors (NFAs) have emerged as tremendous materials, efficiently advancing bulk-heterojunction organic solar cells (OSCs) technology. Unlike their fullerene counterparts, NFAs offer the unique advantage of finely tunable electronic energy levels and optical characteristics, which correspond to substantial enhancement in power conversion efficiency of OSCs. Herein, we have introduced a new series of near-infrared NFAs (AY1-AY8) to advance this technology further. Our research deeply investigates the structure-property relationship and thoroughly explores the optical, optoelectronics, photophysical, and photovoltaic characteristics of a synthetic reference molecule (R) and the modeled AY1-AY8 NFAs series. We performed advanced quantum chemical simulations using density functional theory (DFT) and time-dependent DFT methods. Additionally, we also estimated key geometric characteristics such as frontier molecular orbitals, hole-electron overlap, density of states, molecular electrostatic potential, molecular excitation and binding energies, transition density matrix, and reorganizational energy of electrons and holes and compared them with those of a synthetic reference molecule (R). Our findings show that all designed materials (AY1-AY8) exhibit red-shift absorption, improved electronic charge mobility, and low binding and excitation energies compared to R. Notably, these designed materials (AY1-AY8) display significantly narrower electronic energy gaps (E g 1.89-1.71 eV), indicating enhanced charge shifting from the highest occupied molecular orbital to lowest unoccupied molecular orbital and broadening of the absorption spectrum. Moreover, we also revealed a comprehensive study of the donor/acceptor complex of PTB7-Th/AY8 to understand charge shifting between donor and acceptor molecules. Therefore, we strongly recommend this designed (AY1-AY8) series to the experimentalists for the future development of highly efficient OSC devices.

Anions Regulation of 1D Perovskite Intrusion-Behavior for Efficient and Stable Perovskite Solar Cells.

Constructing a 1D/3D perovskite heterojunction has recently emerged as a prevalent approach for elevating the efficiency and stability of perovskite solar cells (PSCs), due to the excellent defect-passivation capacity and enhanced resistance to water and oxygen of 1D perovskite. However, the 1D perovskite commonly exhibits much poorer charge carrier transport ability when compared with its 3D counterpart. Tailoring the intrusion depth of a 1D perovskite into the 1D/3D heterojunction is thus of key importance for PSCs but remains a great challenge. We introduce herein a novel anion-regulation strategy that can effectively tune the intrusion behavior of 1D perovskite into 3D perovskite to form a 1D/3D heterojunction with gradual structure and gradient energy-level alignment. This gradual 1D/3D-perovskite interface leads to outstanding defect passivation performance, together with a desired balance between charge transport and moisture/oxygen blocking. Consequently, the PSCs with a 1D/3D perovskite heterojunction resulting from tetra-n-butylammonium acetate (TBAAc) treatment yield a remarkable enhancement in power conversion efficiency (PCE) from 18.4 to 20.1%. The unencapsulated device also demonstrates excellent stability and retains 90% of its initial PCE after 2400 h of storage in the air atmosphere with 30 ± 5% humidity at 25 ± 5 °C.

Counter-Doping Effect by Trivalent Cations in Tin-Based Perovskite Solar Cells.

Tin (Sn) -based perovskite solar cells (PSCs) normally show low open circuit voltage due to serious carrier recombination in the devices, which can be attributed to the oxidation and the resultant high p-type doping of the perovskite active layers. Considering the grand challenge to completely prohibit the oxidation of Sn-based perovskites, a feasible way to improve the device performance is to counter-dope the oxidized Sn-based perovskites by replacing Sn2+ with trivalent cations in the crystal lattice, which however is rarely reported. Here, the introduction of Sb3+, which can effectively counter-dope the oxidized perovskite layer and improve the carrier lifetime, is presented. Meanwhile, Sb3+ can passivate deep-level defects and improve carrier mobility of the perovskite layer, which are all favorable for the photovoltaic performance of the devices. Consequently, the target devices yield a relative enhancement of the power conversion efficiency (PCE) of 31.4% as well as excellent shelf-storage stability. This work provides a novel strategy to improve the performance of Sn-based PSCs, which can be developed as a universal way to compensate for the oxidation of Sn-based perovskites in optoelectronic devices.

Depolarization Field-Induced Photovoltaic Effect in Graphene/α-In2Se3/Graphene Heterostructures.

The ferroelectric photovoltaic effect (FPVE) enables alternate pathways for energy conversion that are not allowed in centrosymmetric materials. Understanding the dominant mechanism of the FPVE at the ultrathin limit is important for defining the ultimate efficiency. In contrast to the wide band gap conventional thin-film ferroelectrics, 2D α-In2Se3 has an ideal band gap of 1.3 eV and enables the fabrication of ultrathin and stable heterostructures, providing the perfect platform to explore FPVE in the nanoscale limit. Here, we study the ferroelectric layer thickness-dependent FPVE in vertical few-layer graphene/α-In2Se3/graphene heterostructures. We find that the short-circuit photocurrent is antiparallel to the ferroelectric polarization and increases exponentially with decreasing thickness. We show that the observed behavior is predicted by the depolarization field model, originating from the unscreened bound charges due to the finite density of states in semimetal few-layer graphene. As a result, the heterostructures show enhancement of the power conversion efficiency, reaching 2.56 × 10-3% under 100 W/cm2 in 18 nm thick α-In2Se3, approximately 275 times more than the 50 nm thick α-In2Se3. These results demonstrate the importance of the depolarization field at the nanoscale and define design principles for the potential of harnessing FPVE at reduced dimension.

Simulation of multijunction solar cell interfaces for enhancement of the power conversion efficiency

Simulation of multijunction solar cell interfaces for enhancement of the power conversion efficiency

Polyvinyl Chloride-Based Luminescent Downshifting Film with High Flame Retardancy and Excellent UV Resistance for Silicon Solar Cells.

Solar power generation, as a clean energy source, has significant potential for development. This work reports the recent efforts to address the challenge of low power conversion efficiency in photovoltaic devices by proposing the fabrication of a luminescence downshifting layer using polyvinyl chloride (PVC) with added fluorescent dots to enhance light utilization. A photoluminescent microsphere (HCPAM) is synthesized by cross-linking hexachlorocyclotriphosphazene, 2-iminobenzimidazoline, and polyethyleneimine. Low addition of HCPAM can improve the fire safety of PVC films, raising the limiting oxygen index of PVC to 32.4% and reducing the total heat release and smoke production rate values by 14.5% and 42.9%, respectively. Additionally, modified PVC film remains a transparency of 88% and shows down-conversion light properties. When the PVC+1%HCPAM film is applied to the solar cell, the short-circuit current density increases from 42.3 to 43.8mAcm-2, resulting in a 7.0% enhancement in power conversion efficiency. HCPAM also effectively delays the photooxidative aging of PVC, particularly at a 3% content, maintaining the surface morphology and optical properties of PVC samples during ultraviolet aging. This study offers an innovative strategy to enhance the fire and UV-resistant performance of PVC films and expand their applications in protecting and efficiently utilizing photovoltaic devices.

Account of doping photocatalyst for water splitting

In the field of photocatalytic water splitting, the strategy of doping photocatalysts has emerged as a significant and extensively studied approach. Doping can effectively facilitate the modification of both the microstructure and energy band structure of the photocatalyst, addressing key performance limitations such as light absorption, position of the conduction and valence band minima (CBM and VBM), photogenerated carrier separation, and surface chemical reactions. In recent years, we have reported several works about the doping of rare earth elements into bismuth-based composite oxides. These endeavors are aimed at enhancing the conduction band minimum and achieving overall water splitting under visible light. Based on these bismuth-based composite oxides, we studied the effects of doping on the microstructures of photocatalysts, including exposed surfaces, surface properties, and defects. Recently, we introduce an innovative asymmetric doping technique—Selected Local Gradient Doping, intricately placing doped ions within nanocapsules. This approach allows for the gradual, controlled, and localized release of doped ions to the primary photocatalyst. Therefore, this account is to review our related research in the field of doping for photocatalytic water splitting. The primary focus on doping bismuth-based composite oxides and Asymmetry doping would significantly make contribution to the exploration of novel materials for photocatalytic water splitting under visible light and the enhancement of energy conversion efficiency.

Vacuum-Processed Propylene Urea Additive: A Novel Approach for Controlling the Growth of CH3NH3PbI3 Crystals in All Vacuum-Processed Perovskite Solar Cells.

In this study, we present a novel method for controlling the growth of perovskite crystals in the vacuum thermal evaporation process by utilizing a vacuum-processable additive, propylene urea (PU). By coevaporation of perovskite precursors with PU to form the perovskite layer, PU, acting as a Lewis base additive, retards the direct reaction between the perovskite precursors. This facilitates a larger domain size and reduced defect density. Following the removal of the residual additive, the perovskite layer, exhibiting improved crystallinity, demonstrates reduced charge recombination, as confirmed by a time-resolved microwave conductivity analysis. Consequently, there is a notable enhancement in open-circuit voltage and power conversion efficiency, increasing from 1.05 to 1.15 V and from 17.17 to 18.31%, respectively. The incorporation of a vacuum-processable and removable Lewis base additive into the fabrication of vacuum-processed perovskite solar cells offers new avenues for optimizing these devices.

Optimization of boron depletion for boron-doped emitter of N-type TOPCon solar cells

During the preparation of boron-doped emitters for TOPCon solar cells, boron atoms accumulate, forming a boron-rich layer (BRL). Oxidation, during the boron diffusion process, can eliminate the BRL. Prolonged oxidation which forms a SiO2 layer can remove the BRL, also act as a protective mask for the front surface. Nevertheless, during high-temperature thermal oxidation, boron will be redistributed. Boron reaches a higher equilibrium concentration in SiO2 than in the silicon wafer, and the SiO2/Si interface shifts inward during SiO2 formation. Simultaneously, the high temperature during oxidation prompts the boron inside the silicon wafer to diffuse deeper. The dual effects of oxidation and diffusion cause boron to be depleted near the surface of the silicon wafer. Boron depletion leads to a reverse bending of the energy band, which hampers carrier collection and impedes further enhancement of cell power conversion efficiency. In this paper, the oxidation process was mainly adjusted to reduce surface boron depletion, resulting in approximately 0.09%abs. increase in power conversion efficiency compared to pre-optimization.

Facile synthesis and application of hyperbranched TiO2 hollow spheres for enhancement of power conversion efficiency of CdSeTe quantum dot-sensitized solar cells

Facile synthesis and application of hyperbranched TiO2 hollow spheres for enhancement of power conversion efficiency of CdSeTe quantum dot-sensitized solar cells

Introduction of Co atoms into CdS thin films for improving photovoltaic properties

This paper represents a systematic work on the fabrication of chemical bath-grown CdS films with and without Co atoms and their photovoltaic performances in hybrid solar cells. Structural properties showed 1% Co-doping promoted crystal quality of CdS films. However, a poor crystal quality was developed above 3% Co concentrations. A reduction in sphere size of CdS samples was observed for 1% Co-doping which was ascribed to slow growth of film. Optical examination demonstrated CdS films with 1% Co-doping displayed the highest transparency of 85% in the visible and near-infrared regions, which were explained by the improvement of crystal quality. A maximum band gap of 2.43 eV was found for 1% Co-doped CdS films, whereas an increase in Co concentration to 7% led to a decline in the band gap of CdS that was attributed to sp-d exchange interaction. Photoluminescence data showed Co-doped CdS films had lower PL peak intensity than that of CdS, demonstrating a decrease in the number of intrinsic defects. Photovoltaic measurements displayed that the best efficiency of 0.488% was achieved for CdS-based device including 1% Co atoms, which were almost a seven-fold boost in overall efficiency compared to bare CdS-based device. The enhancement in power conversion efficiency originated from an increase in short-circuit current density of 1% Co-doped CdS-based photovoltaic cell.

Tri-chalcogenides (Sb2S3/Bi2S3) solar cells with double electron transport layers: design and simulation

To make technology accessible to everyone, it is essential to focus on affordability and durability of the devices. Antimony trisulfide (Sb2S3) and bismuth (III) sulfide (Bi2S3) are low-cost and stable materials that are commonly used in photovoltaic devices due to their non-toxic nature and abundance. These materials are particularly promising for photovoltaic applications as they are effective light-absorbing materials. In this study, we utilized the Solar cell Capacitance Simulator- One-Dimensional (SCAPS-1D) software to investigate the parameters of a double electron transport layer (ETL) solar cell based on Sb2S3/ Bi2S3. The parameters examined included thickness of the absorber layer, overall defect density, density of acceptors, radiative recombination coefficient, series and shunt resistance, and work function of the back contact. The solar cell structure studied was FTO/SnO2/CdS/ Sb2S3 and Bi2S3/Spiro-OMeTAD/Au. By incorporating a SnO2 electron transport layer (ETL) into the double ETL structure of Sb2S3 and Bi2S3 solar cells, we observed a significant enhancement in the power conversion efficiency (PCE). Specifically, the PCE increased to 19.71% for the Sb2S3 solar cell and 24.05% for the Bi2S3 solar cell. In contrast, without SnO2, the single ETL-based CdS solar cell achieved a maximum PCE of 18.27 and 23.05% for Sb2S3 and Bi2S3, respectively.

Multitone Waveform Design Toward Enhancing Conversion Efficiency for RF Electronics Detection

Multitone Waveform Design Toward Enhancing Conversion Efficiency for RF Electronics Detection