Enhanced Power Conversion Efficiency Research Articles

Effects of magnetic-elastic anisotropy on magnetoelectric gyrator with ferrite/PZT/ferrite laminate for enhancement of power conversion efficiencies

Effects of magnetic-elastic anisotropy on ferrite/lead zirconate titanate (PZT)/ferrite magnetoelectric (ME) gyrators were investigated for power conversion efficiency further improvement, and a methodology was introduced by changing the direction of applied magnetic field (HDC). Simulation by using finite element method provides a clear evolution of magnetic flux density distribution in ferrite as HDC rotates. Consequently, enhanced ME coupling as well as power conversion efficiency (PE) was achieved under a certain angle with maximum effective magnetic field applied especially at intensive magnetic fields. Experimental results show that current (I)-voltage (V) versus directional angle (θ) between HDC direction and longitudinal direction of ME sample and PE vs θ data can essentially track the dynamic piezomagnetic coefficient (DPMC) vs θ profile, indicating that the HDC rotation induced anisotropic magneto-elastic variations are responsible for the eventual PE improvement. For higher HDC = 98Oe, PE reaches its maximum of 76.5% at θ = 75˚ relative to its counterpart of 47.6% at θ = 0˚, exhibiting an approximately 1.69 times higher enhancement. Therefore, the feasibility of an efficient approach was verified by the obtained results, providing possibilities for PE further improvement and enhanced flexibilities for ME gyrator design.

Asymmetric Glycolated Substitution for Enhanced Permittivity and Ecocompatibility of High-Performance Photovoltaic Electron Acceptor.

Traditional organic photovoltaic materials exhibit low dielectric constants (εr) of 3 to 4, restricting the further enhancement of power conversion efficiencies (PCEs) of organic solar cells (OSCs). Herein we design and synthesize a fused-ring electron acceptor named Y6-4O through introducing an asymmetric highly polarizable oligo(ethylene glycol) side chain onto the pyrrole unit of Y6. Compared with alkylated Y6 (εr = 3.36), asymmetric glycolated Y6-4O shows a notably higher εr value of 5.13 and better solubility in nonhalogen solvents. Because of the higher εr value, the devices based on as-cast PM6:Y6-4O processed using toluene exhibit a higher charge separation yield, slower bimolecular recombination kinetics, and less voltage loss relative to the control devices based on PM6:Y6. Consequently, a high PCE of 15.2% is achieved for PM6:Y6-4O-based devices, whereas the PM6:Y6-based devices show PCEs of only 7.38%. 15.2% is the highest PCE for the as-cast nonhalogenated processed OSC devices, and it is also much higher than the values (<8.5%) reported for OSCs based on high-permittivity (εr > 5) organic photovoltaic semiconductors.

Easy-to-fabricate high efficiency silicon nanowires solar cell modified by CdTe and zinc tetraphenyl porphyrin nanostructures

Liquid junction solar cell (LJSC) with vertically silicon nanowires (SiNWs) as the primary photosensitizer, co-sensitized with luminescent and narrow gap CdTe nanoparticles, and cuboidal microstructures of zinc tetraphenyl porphyrin (ZnTPP) dye offers broad and intense visible light absorption that translates into a maximum power conversion efficiency (PCE) of 9.09%, when combined with a polymeric gel of a I2/I− redox couple as the hole transport material and a counter electrode (CE) of poly(3,4-ethyelenedioxythiophene) doped with imide ions (PEDOT-N(CF3SO2)2), under 1 sun irradiance. The p-type CdTe efficiently scavenges holes from SiNWs and simultaneously allows the passage of photoexcited electrons from ZnTPP to SiNWs via electrical conduction thus imparting an enhanced solar cell performance. Co-sensitization also supresses back electron transfer effectively, as is inferred from a ~68% enhancement in PCE compared to SiNWs alone. Optimization of the CE entailed the evaluation of the effect of dopant anion: imide versus dicyanamide in PEDOT, and revealed that the presence of macro-cracks in the polymer surface, a deeper work function, and a lower electrical conductance are the shortcomings of the dicyanamide doped PEDOT and reduce the overall PCE, compared to imide. This study brings out how by judicious choice of photoanode and CE components, efficient, stable and easy-to-assemble LJSCs can be developed.

Two‐Step Deposition Approach for Lead Free (NH4)3Sb2I9 Perovskite Solar Cells with Enhanced Open Circuit Voltage and Performance

AbstractIn recent years, development of lead (Pb) free perovskite solar cells (PSCs) has attracted the scientific community because of their stability in air and less toxic nature. Antimony (Sb) based perovskite like‐materials such as (CH3NH3)3Sb2I9 and (NH4)3Sb2I9 have been employed as light absorbers and showed promising features for photovoltaic applications. Herein, we have utilized (NH4)3Sb2I9 as light absorber for the construction of Pb free PSCs. Moreover, we have employed a modified two step procedure for the preparation of (NH4)3Sb2I9. The developed Pb free PSCs device (FTO/CL‐TiO2/m‐TiO2/(NH4)3Sb2I9/HTM/Au) exhibited enhanced power conversion efficiency (PCE) of 0.42 % with open circuit voltage (Voc) of 945 mV.

Immediate and Temporal Enhancement of Power Conversion Efficiency in Surface-Passivated Perovskite Solar Cells.

This work reports strategies for improving the power conversion efficiency (PCE) by capitalizing on temporal changes through the storage effect and immediate improvements by interface passivation. It is demonstrated that both strategies can be combined as shown by PCE improvement in passivated perovskite solar cells (PSCs) upon ambient storage because of trap density reduction. By analyzing the dominant charge recombination process, we find that lead-related traps in perovskite bulk, rather than at the surface, are the recombination centers in both as-fabricated and ambient-stored passivated PSCs. This emphasizes the necessity to reduce intrinsic defects in the perovskite bulk. Furthermore, storage causes temporal changes in band alignment even in passivated PSCs, contributing to PCE improvement. Building on these findings, composition engineering was employed to produce further immediate PCE improvements because of defect reduction in the bulk, achieving a PCE of 22.2%. These results show that understanding the dominant recombination mechanisms within a PSC is important to inform strategies for producing immediate and temporal PCE enhancements either by interface passivation, storage, composition engineering, or a combination of them all to fabricate highly efficient PSCs.

Simultaneous passivation of bulk and interface defects through synergistic effect of anion and cation toward efficient and stable planar perovskite solar cells

Bulk and interface carrier nonradiative recombination losses impede the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). It is highly necessary to develop multifunctional strategy to minimize surface and interface nonradiative recombination losses. Herein, we report a bulk and interface defect passivation strategy via the synergistic effect of anions and cations, where multifunctional potassium sulphate (K2SO4) is incorporated at SnO2/perovskite interface. We find that K+ ions in K2SO4 diffuse into perovskite layer and suppress the formation of bulk defects in perovskite films, and the SO42– ions remain located at interface via the strong chemical interaction with SnO2 layer and perovskite layer, respectively. Through this synergistic modification strategy, effective defect passivation and improved energy band alignment are achieved simultaneously. These beneficial effects are translated into an efficiency increase from 19.45% to 21.18% with a low voltage deficit of 0.53 V mainly as a result of boosted open-circuit voltage (Voc) after K2SO4 modification. In addition, the K2SO4 modification contributes to ameliorated stability. The present work provides a route to minimize bulk and interface nonradiative recombination losses for the simultaneous realization of PCE and stability enhancement by rational anion and cation synergistic engineering.

Intriguing CeO2–TiO2 hybrid nanostructured photoanode resulting up to 46% efficiency enhancement for dye-sensitized solar cells

The harvesting of electrical energy from sunrays with low cost, clean form and prosperity is an excellent progression. In this context, significant advancement has been made in the solar energy area in terms of cell's design to enhance efficiency. Light scattering may benefit solar cells in this aspect by extending the travelling distance of light within the photoelectrode film. In this work, dextran templating high-surface-area contained CeO2 nanoparticles (~22 nm) were employed to improve the power conversion efficiency (PCE) of a TiO2-based dye-sensitized solar cell (DSSCs). Various physicochemical techniques were investigated to characterize the synthesized CeO2 nanoparticles. Synthesized cubic CeO2 nanoparticles were further explored as an additional layer on the top of the synthesized anatase TiO2 nanocube based film to fabricate CeO2–TiO2 hybrid photoanode, encouraging light scattering in DSSCs. A comparative study was undertaken to understand the effect of the CeO2 layer on the synthesized and standard anatase TiO2. The overall power conversion efficiency obtained for hybrid photoanode-based DSSC is 8.92%, ~46% higher than that of TiO2 nanocubes-based photoanode, with a considerably improved open-circuit voltage of 0.83 V under 1 SUN AM 1.5 . In addition, the PCE enhancement is observed only ~8% using standard TiO2 based photoanode under the same condition. The photovoltaic performance highlights that dextran templating CeO2 nanoparticle exhibits a significant impact as the light scattering layer and heterojunction formation when incorporating on top of the anatase TiO2 nanocube resulting in a hybrid photoanode enhancing the PCE of DSSCs. This alternative approach could facilitate the performance of TiO2 based DSSCs towards improving efficiency.

Computational and theoretical study of subphthalocyanine based derivatives by varying acceptors to increase the efficiency of organic solar cells

To enhance power conversion efficiency (PCE) of organic solar cells, four new small molecules were designed with subphthalocyanines (SubPc) as a common donor and different benzene bridged end-capped acceptor groups named as prop-1-yne (X1), 1,2,3,4,5-pentaflouro-6-methoxycyclohexane (X2), benzene-1,2,4,5-tetracarbonitrile (X3), and 1,2-diphenylethyne (X4). Photovoltaic effect and quantum parameters of X1-X4 were computed through DFT and TD-DFT by using a selected hybrid functional B3LYP at 6-31G (d, p). Opto-electronic properties such as, absorption maxima (λmax), band gap, charge mobilities and exciton dynamics of X1-X4 were characterized by analyzing the UV–Visible absorption spectra, frontier molecular orbitals (FMOs), reorganization energies and transition density matrix (TDM), respectively. The computed parameters of all the designed molecules were found to be more efficient than reference molecule R. Among all the designed molecules, the molecule X3 has highest absorption (λmax) at 562 nm, reduced band gap (2.07 eV), least reorganization energies of electrons (λe = 0.00462), hole (λh = 0.00232), better charge delocalization in Transition density matrix analysis, and maximum open-cicuit voltage (Voc) of 1.87 eV as compared with other molecules while least exciton binding energy is exhibited by X1 (0.295 eV). These results indicate that our designed molecules are promising donor materials in improving the device performance of OSCs.

Alloyed (Cu2SnS3)x(ZnS)1−x quantum dots as a hole-transporting layer for efficient and stable perovskite solar cells

In the present study, alloyed (Cu2SnS3)x(ZnS)1−x quantum dots (QDs) were prepared by combining Cu2SnS3 and ZnS. The alloyed (Cu2SnS3)x(ZnS)1−x was applied to perovskite solar cells (PSCs) as an inorganic hole transport layer. The power conversion efficiency (PCE) of the solar cells based on (Cu2SnS3)x(ZnS)1−x was optimized by tuning the content of ZnS. A high PCE of 17.02% was obtained for the solar cells based on the optimized (Cu2SnS3)0.7(ZnS)0.3 quantum dots, while that of the solar cells based on Cu2SnS3 was 15.96%. The experimental data demonstrate that the enhancement of PCE could be due to the high conductivity of the alloyed (Cu2SnS3)0.7(ZnS)0.3 QDs and suitable energy level alignment between the corresponding QDs and perovskite layer. In addition, the PSCs based on the alloyed (Cu2SnS3)0.7(ZnS)0.3 possess superior stability compared with that of the Cu2SnS3 based devices. This work displays that (Cu2SnS3)0.7(ZnS)0.3 QDs can be used as a novel inorganic hole transport material to PSCs.

Graphene-Assisted Zwitterionic Conjugated Polycyclic Molecular Interfacial Layer Enables Highly Efficient and Stable Inverted Perovskite Solar Cells

As an effective strategy to achieve high performance and operational stability in perovskite solar cells (PSCs), numerous studies have been conducted to develop efficient charge transporting materials that possess desirable conductivity, carrier mobility, and stability. Among the great number of candidate materials, graphene has attracted significant attention owing to its remarkable optoelectrical properties and stability. Based on these advantages, in this study, a graphene-assisted electron transport layer (ETL) was developed through functionalization with an n-type semiconducting small molecule, perylene diimide amino N-oxide (PDINO), which simultaneously improved the performance and stability of PSCs. The PDINO-functionalized graphene ETL exhibited suitable energy-level alignment with enhanced carrier mobility, thus resulting in an enhanced power conversion efficiency of 21.2% for the inverted structured PSCs. Moreover, through the hydrophobic surface feature and barrier property of graphene and the π–π interaction of PDINO with the underlying layer of PSCs, notably improved operational stability was achieved using the developed functionalized graphene ETL.

Interfacial gradient energy band alignment modulation via ion exchange reaction toward efficient and stable methylammonium-free Dion-Jacobson quasi-2D perovskite solar cells

Dion-Jacobson (DJ) quasi-2D perovskite solar cells (PSCs) have attracted significant attention owing to its greater potentials in realizing efficient and stable quasi 2D PSCs as compared to Ruddlesden–Popper counterpart. To further enhance power conversion efficiency (PCE) and stability, the fabrication of methylammonium-free formamidinium (FA)-based DJ quasi-2D PSCs is highly desirable. Herein, we report a strategy for constructing gradient energy band alignment by achieving gradient Br doping (GBD) via in situ ion exchange reaction between I− and Br− in FA-based DJ quasi-2D PSCs. First, the gradient energy band alignment can facilitate carrier transport, extraction and transfer. Second, the improved crystallinity and reduced defect density due to recrystallization process are realized after FABr treatment. Finally, the incorporation of Br also contributes to increased device stability. The device with GBD achieves a much higher PCE of 16.75% than control device (13.78%), which is mainly as a consequence of a significantly boosted VOC from 0.970 V to 1.107 V due to suppressed bulk and interfacial nonradiative recombination. The unencapsulated device with GBD maintains 93% of its initial PCE after aging under the relative humidity range of 15–20% for 1600 h, and 91% after aging at 60 °C for 400 h.

Boosting the photovoltaic performance of ladder-type heteroheptacene-based nonfullerene acceptors by incorporating auxochromic groups in the electron-rich core

Nonfullerene acceptors (NFAs) that efficiently harvest sunlight and transport the consequent charge are key to advancing the performance of polymer solar cells (PSCs). Herein we demonstrate that the NFA with alkylthio side-chains incorporated in the heteroheptacene core (MS1) shows a significantly increased molar extinction coefficient and enhanced molecular ordering in comparison with the counterpart with alkyl side-chains (MC1). Therefore, in combination with a benchmark donor polymer (PM6), the resulting MS1-based PSC shows an enhanced power conversion efficiency (PCE) of 14.13% with a fill factor (FF) of 71.66% and a short-circuit current density (Jsc) of 21.70 mA cm−2 comparing with the MC1-based PSC which shows a PCE of 11.87% with a FF of 62.55% and a Jsc of 20.39 mA cm−2. The enhanced photovoltaic performance for the MS1-based PSC can be in part attributed to the increased light-harvesting ability of the MS1-based active layer and in part attributed to its boosted carrier mobilities and reduced charge recombination. Moreover, with an electrode optimization, the best-performing MS1-based PSC shows a further enhanced PCE of 15.01% which is an impressive efficiency among all acceptor–donor–acceptor type NFAs reported to date. This work suggests the important role of the auxochromic groups in the electron-rich core in determining the photovoltaic performance of NFAs.

Hybrid titanium dioxide/sericite light scattering layer to enhance light harvesting of dye-sensitized solar cells

Intensification of light harvesting is an imperative strategy to improve the photovoltaic performance of dye-sensitized solar cells (DSSCs). The typical way is to employ a light scattering layer on top of the photoanode to augment the photon scattering of incident light for light harvesting of dye sensitizers. In this study, we have designed a new light scattering layer consisting of micro-sized sericite flakes and TiO2 nanoparticles, and material optimization is performed by using two sizes of TiO2 nanoparticles (P25-TiO2 of 20-30 nm and B-TiO2 of 30-100 nm) as the matrix to dope sericite flakes. This hybrid scattering layer gives rise to an enhancement of power conversion efficiency of DSSC under 1 sun and low-intensity illuminations. Maximum cell efficiencies of 8.667 % and 8.963 % are recorded for the DSSCs employing P25-TiO2/5 wt% sericite and B-TiO2/25 wt% sericite scattering layer, respectively, at 1 sun illumination, which outperforms that employing pure TiO2 scattering layer (8.2 %). Maximum cell efficiencies of 22.936 % and 23.121 % are optimized at 6,000 lux following the same TiO2/sericite hybrid systems. Such addition of sericite in the scattering layer indeed enhances the light harvesting performance and offers a new pathway to prepare more efficient light scattering layer.

Novel indole-based photosensitizers coupled with PEG-HEC quasi-solid-state electrolyte to improve energy conversion and stability of organic dyes based-dye sensitized solar cells

A series of novel Indole based organic dyes were synthesized and coupled with a Poly-ethylene glycol-Hydroxy ethyl cellulose quasi-solid-state-electrolyte (PEG-HEC QSSE) polymer blended iodine electrolyte to obtain a metal-free dye-based dye-sensitized solar cell (DSSCs) with better stability. The newly synthesized organic dyes were confirmed through 1H, 13C NMR, CHN analysis. The optical and electrochemical properties of the dyes were determined using UV-visible spectrometry and cyclic voltammetry techniques. A quasi-solid state (QSS) blended polymer PEG-HEC with iodide redox couple as electrolyte was characterized via Field emission Scanning Electron microscope (FE-SEM), UV-visible spectroscopy, XRD and DSC. A foremost comparative study was analysed on DSSC devices with the newly synthesised organic dyes (DPC, DTC, DPCY, DTCY, DPTCY and DTTCY) coupled with the QSSE. The electrochemical impedance spectrum was discussed for all the six dyes coupled with PEG-HEC QSSE, among that DTTCY sensitized device exhibits good ionic conductivity (1.13 × 10−3 S cm−1), high chemical capacitance (Cµ=17.01 µF), high recombination resistance (53.97 Ω) and lower charge transfer resistance (2.35 Ω) due to the presence of a strong electron-withdrawing group in the organic dye and also QSS behaviour of electrolyte. The longer electron lifetime (τn-58.51 ms) and better diffusion coefficient (4.25 × 10−7 cm2 s−1) of the device prove the short circuit current (Jsc= 16.39 mA cm−2) and enhancement of power conversion efficiency (PCE) of 6.24 % with better stability under AM 1.5 G illumination (100 mW cm−2). The combination of new Indole based organic dyes with PEG-HEC QSSE paved a way to improve the PCE and stability of organic dyes based DSSCs.

Surface Evolution and Fractal Dimensions of CH3NH3PbI3-XClX Thin Films and its Photovoltaic Performance

We fabricated the CH 3 NH 3 PbI 3-X Cl X perovskite crystalline films by solution processed method in air and nitrogen ambience to investigate the impact of the growth conditions on surface morphology and interface properties of the films. The surface morphology of CH 3 NH 3 PbI 3-X Cl X thin films are captured by scanning electron microscopy (SEM) and fractal analysis is performed on SEM micrographs. The value of fractal dimension/hurst exponent is found to be larger/smaller in N 2 environment as comparison to open air environment. The greater value of fractal dimension is corresponding to larger surface jaggedness which plays a crucial role for improving the interface between the perovskite and hole transportation layer. Furthermore, this analytical prediction is confirmed by photovoltaic devices fabricated on these films and observed a 60% enhancement in power conversion efficiency (PCE) of N 2 environment based thin films as compare to open air processed films. This may be due to the formation of compact and voids free perovskite self-affine fractal surfaces under nitrogen environment as compare to open air environment. Our findings represent a step forward to the realization of the peculiar morphological behaviour of the mixed halide perovskite fabricated in different environmental conditions.

Grain boundary defect passivation by in situ formed wide-bandgap lead sulfate for efficient and stable perovskite solar cells

The trap-assisted nonradiative recombination at grain surface and grain boundary (GB) of perovskite films impede the further improvement of power conversion efficiency (PCE) and stability of perovskite solar cells (PSCs). In addition, the poor moisture stability of perovskite films hinders the commercial application of PSCs. Herein, we report a multifunctional GB modification strategy where the wide-bandgap hydrophobic PbSO4 modification layer is in situ formed at the GBs of perovskite films through the reaction between methylamine sulfate and PbI2. It is revealed that multiple functions are achieved after the formation of PbSO4 modification layer, including crystallization improvement, defect passivation, and hydrophobicity improvement. As a result, the PbSO4 modified device exhibits a PCE enhancement from 19.53% to 21.90% as compared to the control device. Moreover, up to 71% of its initial PCE is maintained for the unencapsulated PbSO4 modified device after aging under a relative humidity of 80 ± 5% for 250 h. This work proposes an effective multifunctional approach to modify the GBs of perovskite films for the purpose of simultaneous increasement of PCE and stability.

Multifunctional Crosslinking-Enabled Strain-Regulating Crystallization for Stable, Efficient α-FAPbI3 -Based Perovskite Solar Cells.

α-Formamidinium lead triiodide (α-FAPbI3 ) represents the state-of-the-art for perovskite solar cells (PSCs) but experiences intrinsic thermally induced tensile strain due to a higher phase-converting temperature, which is a critical instability factor. An in situ crosslinking-enabled strain-regulating crystallization (CSRC) method with trimethylolpropane triacrylate (TMTA) is introduced to precisely regulate the top section of perovskite film where the largest lattice distortion occurs. In CSRC, crosslinking provides in situ perovskite thermal-expansion confinement and strain regulation during the annealing crystallization process, which is proven to be much more effective than the conventional strain-compensation (post-treatment) method. Moreover, CSRC with TMTA successfully achieves multifunctionality simultaneously: the regulation of tensile strain, perovskite defects passivation with an enhanced open-circuit voltage (VOC = 50mV), and enlarged perovskite grain size. The CSRC approach gives significantly enhanced power conversion efficiency (PCE) of 22.39% in α-FAPbI3 -based PSC versus 20.29% in the control case. More importantly, the control PSCs' instability factor-residual tensile strain-is regulated into compression strain in the CSRC perovskite film through TMTA crosslinking, resulting in not only the best PCE but also outstanding device stability in both long-term storage (over 4000 h with 95% of initial PCE) and light soaking (1248 h with 80% of initial PCE) conditions.

Cost Effective Solvothermal Method to Synthesize Zn-Doped TiO2 Nanomaterials for Photovoltaic and Photocatalytic Degradation Applications

Titanium dioxide (TiO2) is a commonly used wide bandgap semiconductor material for energy and environmental applications. Although it is a promising candidate for photovoltaic and photocatalytic applications, its overall performance is still limited due to low mobility of porous TiO2 and its limited spectral response. This limitation can be overcome by several ways, one of which is doping that could be used to improve the light harvesting properties of TiO2 by tuning its bandgap. TiO2 doped with elements, such as alkali-earth metals, transition metals, rare-earth elements, and nonmetals, were found to improve its performance in the photovoltaic and photocatalytic applications. Among the doped TiO2 nanomaterials, transition metal doped TiO2 nanomaterials perform efficiently by suppressing the relaxation and recombination of charge carriers and improving the absorption of light in the visible region. This work reports the possibility of enhancing the performance of TiO2 towards Dye Sensitised Solar Cells (DSSCs) and photocatalytic degradation of methylene blue (MB) by employing Zn doping on TiO2 nanomaterials. Zn doping was carried out by varying the mole percentage of Zn on TiO2 by a facile solvothermal method and the synthesized nanomaterials were characterised. The XRD (X-Ray Diffraction) studies confirmed the presence of anatase phase of TiO2 in the synthesized nanomaterials, unaffected by Zn doping. The UV-Visible spectrum of Zn-doped TiO2 showed a red shift which could be attributed to the reduced bandgap resulted by Zn doping. Significant enhancement in Power Conversion Efficiency (PCE) was observed with 1.0 mol% Zn-doped TiO2 based DSSC, which was 35% greater than that of the control device. In addition, it showed complete degradation of MB within 3 h of light illumination and rate constant of 1.5466×10−4s−1 resembling zeroth order reaction. These improvements are attributed to the reduced bandgap energy and the reduced charge recombination by Zn doping on TiO2.

Electrodeposition of nanostructured bilayer CuI@CuSCN as hole transport material for highly efficient inverted perovskite solar cells

In this article, we implemented a new two-step electrodeposition method for preparing bilayer CuI@CuSCN thin films. The film thickness and optical transparency are controlled by varying electrochemical potential and time. The inverted perovskite solar cells are fabricated using electrodeposited bilayer CuI@CuSCN thin films as a hole transport material (HTM) and carbon as a back electrode. The best performing device showed short circuit current (Jsc) of 20.26 mA/cm2, open-circuit voltage(Voc) of 1.10 V, fill factor (FF) of 0.78 and power conversion efficiency of 20.35% with 2 min grown bilayer CuI@CuSCN HTMs. The electrodeposited bilayer CuI@CuSCN thin films showed a 7.6% enhancement in power conversion efficiency than the previously reported CuI/CuSCN composites. From the observed results, moderate film thickness and uniform morphology of bilayer CuI@CuSCN HTMs provide better photovoltaic performance. The robust nanoclusters of bilayer CuI@CuSCN and used carbon back electrode provides remarkable device stability and charge extraction.

A 6.78 MHz, 95.0% Peak Efficiency Monolithic Two-Dimensional Calibrated Active Rectifier for Wirelessly Powered Implantable Biomedical Devices.

In this paper, a fully integrated active rectifier with triple feedback loops is proposed to enhance power conversion efficiency (PCE) over a wide loading range by calibrating both the gate transition timing and power switch size. The on- and off-transitions of the power switches are calibrated using a hybrid delay-based gate control circuit (HDGCC) with hybrid feedback loops. Conventional active rectifiers that only focused on calibrating the gate transition timing of a NMOS power switch with a fixed power switch size exhibit a low PCE when the loading condition deviates from the predetermined range. Thus, an automatic size selector based on a third feedback loop is proposed, which changes the power switch size based on the loading condition and ensures a stable operation of the hybrid loops by maintaining the voltage drop across the NMOS switches. An active rectifier was fabricated using the standard 0.18 μm CMOS process. The effectiveness and robustness of the two-dimensional calibration were verified through measurements under an AC input voltage ranging from 2.5 to 5.0 V and an output power ranging from 1.25 to 125 mW. The peak voltage conversion ratio and peak PCE were 97.6% and 95.0%, respectively, at RL = 500 Ω.