Voltage Conversion Efficiency Research Articles

Numerical simulations of 22% efficient all-perovskite tandem solar cell utilizing lead-free and low lead content halide perovskites

Lead-free or low lead content perovskite materials are explored in photovoltaic (PV) devices to mitigate the challenges of toxic lead-based halides. However, the conversion efficiency from such materials is far below compared to its counterparts. Therefore, to make a humble contribution in the development of lead-free or low lead content perovskite solar cells (PSCs) for future thin-film PV technology, a simulation study of tin (Sn) and Pb mixed halide (MAPb0.5Sn0.5I3, 1.22 eV) PSC is carried out in this manuscript. The device is further optimized in terms of transport layer and thickness variation to get 15.1% conversion efficiency. Moreover, the optimized narrow bandgap halide based device is further deployed in the monolithic tandem configuration with lead-free wide bandgap (1.82 eV) halide, i.e. Cs2AgBi0.75Sb0.25Br6, 1.82 eV (WBH) PSC, to mitigate the thermalization as well as transparent E g losses. Filtered spectrum, current matching, and construction of tandem J–V curve at the current matching point are utilized to design the tandem solar cell under consideration. Tandem device delivered short current density, J SC (15.21 mA cm−2), open-circuit voltage, V OC (1.95 V), fill factor, FF (74.09%) and power conversion efficiency, PCE (21.97%). The performance of the devices considered in this work is found to be in good approximation with experimental work.

Un nuevo rectificador reconfigurable CMOS para recolectores de energía piezoeléctrica en dispositivos portables

Wearable energy harvesters have potential application in the conversion of human-motion energy into electrical energy to power smart health-monitoring devices, the textile industry, smartwatches, and glasses. These energy harvesters require optimal rectifier circuits that maximize their charging efficiencies. In this study, we present the design of a novel complementary metal-oxide semiconductor (CMOS) reconfigurable rectifier for wearable piezoelectric energy harvesters that can increase their charging efficiencies. The designed rectifier is based on standard 0.18 µm CMOS process technology considering a geometrical pattern with a total silicon area of 54.765 µm x 86.355 µm. The proposed rectifier circuit has two transmission gates (TG) that are composed of four rectifier transistors with a charge of 45 kΩ, a minimum input voltage of 500 mV and a maximum voltage of 3.3 V. Results of numerical simulations of the rectifier performance indicate a voltage conversion efficiency of 99.4% and a power conversion efficiency up to 63.3%. The proposed rectifier can be used to increase the charging efficiency of wearable piezoelectric energy harvesters.

Mitigating voltage loss in efficient CsPbI2Br all-inorganic perovskite solar cells via metal ion-doped ZnO electron transport layer

CsPbI2Br all-inorganic perovskite solar cells (PSCs) have attracted much attention due to their suitable bandgap and outstanding thermostability. However, the large energy loss of CsPbI2Br PSCs generally endows low open circuit voltage (VOC) and unsatisfactory power conversion efficiency (PCE), which severely hamper its further development. Herein, we proposed a facile route to modify the ZnO electron transporting layer (ETL) by in situ chemical doping strategy with metal ions. The doped ZnO ETL with Pb(Ac)2 or CsAc cannot only effectively tune its energy levels, conductivity, and charge extraction but also ameliorate the crystallization and morphology of upper perovskite films. Particularly, Pb(Ac)2-doped ZnO (ZnO:Pb) induces an energy level offset of 0.15 eV relative to the conduction band of CsPbI2Br with largely reduced Ohmic loss. Thus, the highest VOC is significantly boosted to above 1.3 V for the CsPbI2Br PSCs with a champion PCE of 16.36%, while the reference PSC just yields a moderate PCE of 14.43% with a low VOC of 1.168 V. Moreover, considerable improvements in device stability are achieved for the PSCs with doped ZnO ETLs than those of the ZnO-based device. Our work provides a promising strategy to alleviate the VOC deficit toward the attainment of highly efficient and stable PSCs.

Improving Contact and Passivation of Buried Interface for High‐Efficiency and Large‐Area Inverted Perovskite Solar Cells

AbstractInverted‐structured perovskite solar cells (PSCs) mostly employ poly‐triarylamines (PTAAs) as hole‐transporting materials (HTMs), which generally result in low‐quality buried interface due to their hydrophobic nature, shallow HOMO levels, and absence of passivation groups. Herein, the authors molecularly engineer the structure of PTAA via removing alkyl groups and incorporating a multifunctional pyridine unit, which not only regulates energy levels and surface wettability, but also passivates interfacial trap‐states, thus addressing above‐mentioned issues simultaneously. By altering the linking‐site on pyridine unit from ortho‐ (o‐PY) to meta‐ (m‐PY) and para‐position (p‐PY), they observed a gradually improved hydrophilicity and passivation efficacy, mainly owing to increased exposure of the pyridine‐nitrogen as well as its lone electron pair, which enhances the contact and interactions with perovskite. The open‐circuit voltage and power conversion efficiency (PCE) of inverted‐structured PSCs based on these HTMs increased with the same trend. Consequently, the optimal p‐PY as HTM enables facile deposition of uniform perovskite films without complicated interlayer optimizations, delivering a remarkably high PCE exceeding 22% (0.09 cm2). Moreover, when enlarging device area tenfold, a comparable PCE of over 20% (1 cm2) can be obtained. These results are among the highest efficiencies for inverted PSCs, demonstrating the high potential of p‐PY for future applications.

Simulation of a perovskite sandwich solar cell with the p-CZTS / p-CH3NH3PbCI3 / p-CZTS absorber layers

Perovskite solar cells attract the attention because of their unique properties in photovoltaic cells. Numerical simulation to the structure of Perovskite on p-CZTS/p-CH3NH3PbCI3/p-CZTS absorber layers is performed by using a program solar cell capacitance simulator (SCAPS-1D), with changing absorber layer thickness. The effect of thickness p-CZTS/p-CH3NH3PbCI3/p-CZTS, layers at (3.2μm, 1.8 μm, 1.1 μm) respectively are studied. The obtained results are short circuit current density (Jsc ), open circuit voltage (V oc), fill factor (F. F) and power conversion efficiency (PCE) equal to (28 mA/cm2, 0.83 v, 60.58 % and 14.25 %) respectively at 1.1 μm thickness. Our findings revealed that the dependence of current - voltage characteristics on the thickness of the absorbing layers, an increase in the amount of short circuit current density with an increase in the thickness of the absorption layers and thus led to an increase in the conversion efficiency and improvement of the cell by increasing the thickness of the absorption layers.

3‐D Modeling of Ultrathin Solar Cells with Nanostructured Dielectric Passivation: Case Study of Chalcogenide Solar Cells (Adv. Theory Simul. 11/2021)

3-D Modeling of Ultrathin Solar Cells In article number 2100191, Waseem Raja, Erkan Aydin, Thomas G. Allen, and Stefaan De Wolf develop a novel 3-D optoelectrical finite-element model to analyze the performance of ultrathin solar cells. In particular, the 3-D model investigates the light trapping and field passivation in which the negative charges induced on the nanostructured passivation layer repel the minority charge carriers, increasing the solar cell's open-circuit voltage and power conversion efficiency.

Distinguishing bulk and surface recombination in CdTe thin films and solar cells using time-resolved terahertz and photoluminescence spectroscopies

Understanding the nature of recombination and its dependence on defects and interfaces is essential for engineering materials and contacts for a higher open-circuit voltage (Voc) and power conversion efficiency in photovoltaic (PV) devices. Time-resolved photoluminescence (TRPL) has conventionally been used to evaluate recombination, but carrier redistribution often dominates the response at short times. Here, we report on the quantification of carrier dynamics and recombination mechanisms by complementary use of both time-resolved terahertz spectroscopy and TRPL combined with numerical modeling of the continuity equations and Poisson's equation. We have demonstrated this approach using CdTe thin films. A thin-film stack with CdTe fabricated by vapor transport deposition and treated with CdCl2 exhibited a bulk lifetime of 1.7 ± 0.1 ns, a negligible CdTe/CdS interface recombination velocity, and a back surface recombination velocity of 6.3 ± 1.3 × 104 cm/s. In contrast, a film stack without CdCl2 treatment had a bulk lifetime of only 68 ± 12 ps and a higher interface recombination velocity of 4 ± 2 × 108 cm/s. By determining the locus and mechanisms of performance-limiting recombination, we can accelerate the development of thin-film PVs with higher Voc and efficiency. While the method has been demonstrated here using CdTe, it is also applicable to perovskites, Cu(InGa)Se2, Cu2ZnSn(S,Se)4, and emerging technologies.

Enhanced efficiency in hollow core electrospun nanofiber-based organic solar cells

Over the last decade, nanotechnology and nanomaterials have attracted enormous interest due to the rising number of their applications in solar cells. A fascinating strategy to increase the efficiency of organic solar cells is the use of tailor-designed buffer layers to improve the charge transport process. High-efficiency bulk heterojunction (BHJ) solar cells have been obtained by introducing hollow core polyaniline (PANI) nanofibers as a buffer layer. An improved power conversion efficiency in polymer solar cells (PSCs) was demonstrated through the incorporation of electrospun hollow core PANI nanofibers positioned between the active layer and the electrode. PANI hollow nanofibers improved buffer layer structural properties, enhanced optical absorption, and induced a more balanced charge transfer process. Solar cell photovoltaic parameters also showed higher open-circuit voltage (+ 40.3%) and higher power conversion efficiency (+ 48.5%) than conventional architecture BHJ solar cells. Furthermore, the photovoltaic cell developed achieved the highest reported efficiency value ever reached for an electrospun fiber-based solar cell (PCE = 6.85%). Our results indicated that PANI hollow core nanostructures may be considered an effective material for high-performance PSCs and potentially applicable to other fields, such as fuel cells and sensors.

Simulating the Performance of a Formamidinium Based Mixed Cation Lead Halide Perovskite Solar Cell.

With the aim of decreasing the number of experiments to obtain a perovskite solar cell (PSC) with maximum theoretical efficiency, in this paper, PSC performance was studied using the program solar cell capacitance simulator (SCAPS-1D). The PSC with the architecture ITO/TiO2/perovskite/spiro-MeOTAD/Au was investigated, while the selected perovskite was mixed cation Rb0.05Cs0.1FA0.85PbI3. The analysis was based on an experimentally prepared solar cell with a power conversion efficiency of ~7%. The PSC performance, verified by short-circuit current density (Jsc), open-circuit voltage (Voc), fill factor (FF) and power conversion efficiency (PCE), was studied by optimization of the simulation parameters responsible for improvement of the cell operation. The optimized parameters were absorber layer thickness, doping, defect concentration and the influence of the resistivity (the net effect of ohmic loss, Rs and the leakage current loss represented by the resistivity, Rshunt). The results of SCAPS-1D simulations estimated the theoretical power conversion efficiency of 15% for our material. We have showed that the main contribution to improvement of solar cell efficiency comes with lowering ohmic resistivity of the cell as well as doping and defect concentration, because their concentration is proportional to recombination rate.

A Dynamic Threshold Cancellation Technique for a High-Power Conversion Efficiency CMOS Rectifier.

Power conversion efficiency (PCE) has been one of the key concerns for power management circuits (PMC) due to the low output power of the vibrational energy harvesters. This work reports a dynamic threshold cancellation technique for a high-power conversion efficiency CMOS rectifier. The proposed rectifier consists of two stages, one passive stage with a negative voltage converter, and another stage with an active diode controlled by a threshold cancellation circuit. The former stage conducts the signal full-wave rectification with a voltage drop of 1 mV, whereas the latter reduces the reverse leakage current, consequently enhancing the output power delivered to the ohmic load. As a result, the rectifier can achieve a voltage and power conversion efficiency of over 99% and 90%, respectively, for an input voltage of 0.45 V and for low ohmic loads. The proposed circuit is designed in a standard 130 nm CMOS process and works for an operating frequency range from 800 Hz to 51.2 kHz, which is promising for practical applications.

Improving Photovoltaic Performance of Dye-Sensitized Solar Cell by Modification of Photoanode With g-C3N4/TiO2 Nanofibers

In order to improve the photovoltaic performance of dye-sensitized solar cell (DSSC), graphitic carbon nitride (g-C3N4)/titanium dioxide (TiO2) nanofibers (NFs) are added into the photoanode of DSSC as an additional layer. g-C3N4 is prepared by high-temperature calcination. Through sol–gel method and electrospinning technology, we prepare g-C3N4/TiO2 NFs. The material properties of g-C3N4/TiO2 NFs are characterized through X-ray diffraction (XRD), ultraviolet-visible (UV-Vis), and field emission scanning electron microscope (FE-SEM). From the measurements of electrochemical impedance spectroscopy (EIS), incident photon to current efficiency (IPCE), and ${J}-{V}$ characteristics, the performances of the DSSCs are analyzed, including impedance parameters, short-circuit current density, open-circuit voltage, fill factor, and photoelectric conversion efficiency. The results show that the addition of g-C3N4/TiO2 NFs is able to enhance the photovoltaic performance. The photoelectric conversion efficiency of the modified DSSC is increased to 5.22%. Compared with the photoelectric conversion efficiency of the DSSC without modification (4.11%), it is an increase of 27%.

Improving energy harvesting efficiency of dye sensitized solar cell by using cobalt-rGO co-doped TiO2 photoanode

In dye-sensitized solar cells (DSSCs), TiO2 has long been a popular electron transport material for carrying photo-generated electrons from the dye to the outer circuit. However, increasing the electrical conductivity of TiO2 while preserving its properties is one of the most significant challenges for increasing DSSC efficiency. Here, cobalt-reduced graphene oxide co-doped TiO2 nanoparticles were synthesized by a modified sol-gel procfess that together controlled the particle size as well as narrowed bandgap of nanoparticles as determined by XRD and UV-Vis absorption measurements. The SEM and TEM were used to perform in-depth morphological characterization of the newly synthesized nanocomposites while J-V (current-voltage) curves, EIS Nyquist curves, and incident photon to current conversion efficiency (IPCE) spectra were used to examine the photovoltaic parameters. Enhanced short circuit current density (Jsc 12.83 mA cm−2), open-circuit voltage (Voc 0.618 V) and overall power conversion efficiency (PCE, η = 5.24%) of DSSC was obtained with Co/rGO co-doped TiO2 based photoanode in comparison to bare TiO2 (η = 3.71%), cobalt doped TiO2 (η = 4.09%) and rGO doped TiO2 (η = 4.43%) based DSSCs. Huge improvement in efficiency, 41% higher PEC in Co/rGO co-doped TiO2, was attributed to better utilization of visible radiations, greater dye adsorption and enhancement in charge transfer properties by suppressing the electron transport resistances. The incorporation of rGO improved electron transfer, which compensated for recombination losses, thereby increasing the DSSC's Jsc. The synergetic role of rGO and transition metal helped in keeping the structure intact in the nano-assembly that enhance the photo-generated carriers.

Hydroxyl‐Rich d‐Sorbitol to Address Transport Layer/Perovskite Interfacial Issues toward Highly Efficient and Stable 2D/3D Tin‐Based Perovskite Solar Cells

Abstract2D/3D mixed tin (Sn)‐based perovskites serving as excellent active layers possess a potential for enhancing film/device stabilities, open‐circuit voltage, and power conversion efficiency (PCE) of perovskite solar cells (PSCs). Unfortunately, the poor morphology and low film coverage of these 2D/3D perovskites jeopardize their device performance and stability. Herein, doping of hydroxyl‐rich d‐sorbitol into hole transport layer poly(3,4‐ethenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) can effectively address the PEDOT:PSS/perovskite interfacial issues. The multihydroxyl groups from d‐sorbitol can sufficiently anchor iodide ions ([SnI6]4− or free I−) of PEA0.1(FA0.75MA0.25)0.9SnI3 perovskite via hydrogen bond, which not only introduces more nucleation sites with improved crystallinity along the preferential crystal orientations, but also reduces the trap states’ density and suppresses the iodide ions’ migration. In the meanwhile, the content of SnI2 is reduced in the resulting perovskite films. All of these are conducive to form compact and smooth high‐quality perovskite films with less traps and enhanced stability. Benefitting from these, an inverted PSC with a champion PCE of 10.46% and a lifetime of 700 h (25% attenuation in N2) is eventually achieved. This work provides a promising approach to manufacture highly efficient and stable Sn‐based PSCs based on 2D/3D mixed perovskites.

Perovskite semiconductor-engineered cascaded molecular energy levels in naturally-sensitized photoanodes

Naturally-sensitized photoanodes in dye-sensitized solar cells (DSSCs) are promising alternatives to enhance photoabsorption, electron excitation/injection, but voltage loss remains a challenge. Here, we focus on understanding the cascading of energy levels in perovskite semiconductor cosensitized naturally-sensitized photoanodes to leverage forward charge transport addressing the voltage loss arising from ITO/TiO2 heterojunction's built-in potential. The β-carotene-sensitized TiO2 photoanode modified with methylammonium lead iodide (MAPbI3) co-sensitizer causes an upward shifting in TiO2 Fermi level (EF). This phenomenon is predominantly attributed to increased initially injected electrons due to low MAPbI3 bandgap and high visible-light absorption. Enhanced charge separation and injection mechanisms at the TiO2/MAPbI3 interface increase the effective density-of-states (DOS >2.46 × 1021 cm−3) in the TiO2 conduction band (CB) and hence decrease its work function to 4.82 eV. The decrease in TiO2 work function suppressed CB bending at ITO/TiO2 heterojunction, which minimized the photoinduced electrostatic potential barrier up to 13.1%. The reduced Schottky barrier (φSBH<0.52 eV) only allows electrons tunneling, while inhibited back-electron transport reduced both current leakage and voltage loss yielding in high open-circuit voltage (Voc increase by 120%) and power conversion efficiency (PCE increase by 240%). The MAPbI3 incorporation also broadened photoanode absorbance by 2-fold, paving the way towards perovskite semiconductor cosensitization to avoid voltage loss from bio-integrated photoanodes for photovoltaic and other optoelectronic and photonic applications. Future works will focus on studying the series resistance, cathode electrode coating uniformity, recombination kinetics, solid electrolytes, as well as other aspects typically related to increasing the photocurrent levels of this β-carotene-sensitized solar cell.

Effect of PEDOT:PSS composition on photovoltaic performance of PEDOT:PSS/n-Si hybrid solar cells

Poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonic acid) (PEDOT:PSS) with different composition ratios (α = [PSS]/[PEDOT]) was newly synthesized by chemical oxidative polymerization and organic/inorganic heterojunction hybrid solar cells were fabricated by spin-coating of the PEDOT:PSS water dispersion on n-type silicon wafer. It was found that the photovoltaic performance of the hybrid solar cells was strongly affected by electrical and optical properties of the PEDOT:PSS, where at α = 2.8 the short-circuit current (J sc), open-circuit voltage (V oc), and power conversion efficiency attained 32.1 mA cm−2, 0.521 V, and 11.1%, respectively.

An Ultra-Low-Power, Self-Start-Up DC-DC Boost Converter for Self-Powered IoT Node

This paper presents an ultra-low-power boost converter for self-powered IoT applications to self-start and power-up IoT devices from scratch without any requirement of an external start-up. The proposed converter and its clock generator operate in sub-threshold utilizing bulk-driven technique for low-power operation. The bulk-driven technique improves charge transfer switches for effective switching using auxiliary transistors. This approach enables a MOSFET to operate on supplies lower than its threshold voltage with a significant reduction in the reverse charge transfer and switching loss while increasing the voltage conversion efficiency and output voltage. To validate the performance of the proposed architecture, the post-layout simulation is carried out in standard CMOS 0.18[Formula: see text][Formula: see text]m technology. Under low-voltage supply of 0.4[Formula: see text]V, the simulated transient output voltage takes 110[Formula: see text][Formula: see text]s to reach 1.92[Formula: see text]V with 0.15[Formula: see text] output voltage ripple, while consuming the power of 772[Formula: see text]nW.

A High Power-Conversion-Efficiency Voltage Boost Converter with MPPT for Wireless Sensor Nodes.

A high power-conversion-efficiency voltage boost converter with MPPT for wireless sensor nodes (WSNs) is proposed in this paper. Since tiny wireless sensor nodes are all over complex environments, an efficient power management system (PMS) must be equipped to achieve long-term self-power supply and maintain regular operation. It is common to use Photovoltaic cells (PV) to harvest sunlight in the environment. However, most existing interface boost integrated circuits for the PV cell have low efficiency. This paper presents a voltage boost converter (VBC) with high power conversion efficiency (PCE) for WSNs. The integrated circuit (IC) designed in this paper includes a novel four-phase high-efficiency charge pump module, an ultra-low-power perturbation observation (P&O) MPPT control circuit module, a feedback control module, a nano-ampere current reference, etc. Manufactured in a standard 0.35 um complementary metal-oxide-semiconductor (CMOS) technology, the chip area is 3.15 mm × 2.43 mm. Test results demonstrate that when the output voltage of the PV cell is more than 0.5 V, VBC can improve the voltage to 3Vin, and the calculated voltage conversion efficiency can reach 99.4%. P&O MPPT algorithm makes output power improving 8.53%. Furthermore, when the output load current is 297uA, the output PCE achieves 85.1%.

Design and Analysis of DC/DC Boost Converter Using Vertical GaN Power Device.

In this study, a high-performance vertical gallium nitride (GaN) power transistor is designed by using two-dimensional technology computer-aided design simulator. The vertical GaN transistor is used to analyze the DC/DC boost converter. The systems requiring high voltages of 1000 V or more, such as electric vehicles, need wide devices to achieve a high breakdown voltage when using conventional power devices. However, vertical GaN transistors can be fabricated with small device area and high breakdown voltage. The proposed device has an off-current of 4.72×10-10 A/cm², an on-current of 17,528 A/cm², and a high breakdown voltage of 1,265 V due to good gate controllability and the very long gate-to-drain length. Using the designed device, a boost converter that doubles the input voltage was constructed and is characteristics were examined. The designed boost converter obtained an output voltage of 1,951 V and the voltage conversion efficiency was considerably high at 97.55% when the input voltage was 1,000 V.

Composite electron transport layer for efficient N-I-P type monolithic perovskite/silicon tandem solar cells with high open-circuit voltage

Perovskite/silicon tandem solar cells (PSTSCs) have exhibited huge technological potential for breaking the Shockley-Queisser limit of single-junction solar cells. The efficiency of P-I-N type PSTSCs has surpassed the single-junction limit, while the performance of N-I-P type PSTSCs is far below the theoretical value. Here, we developed a composite electron transport layer for N-I-P type monolithic PSTSCs with enhanced open-circuit voltage (VOC) and power conversion efficiency (PCE). Lithium chloride (LiCl) was added into the tin oxide (SnO2) precursor solution, which simultaneously passivated the defects and increased the electron injection driving force at the electron transfer layer (ETL)/perovskite interface. Eventually, we achieved monolithic PSTSCs with an efficiency of 25.42% and VOC of 1.92 V, which is the highest PCE and VOC in N-I-P type perovskite/Si tandem devices. This work on interface engineering for improving the PCE of monolithic PSTSCs may bring a new hot point about perovskite-based tandem devices.

Methylamine Gas Treatment Affords Improving Semitransparency, Efficiency, and Stability of CH3NH3PbBr3‐Based Perovskite Solar Cells

High bandgap semitransparent solar cells based on CH3NH3PbBr3 perovskites are attractive for building integration, tandem cells, and electrochemical applications. The lack of control of the CH3NH3PbBr3 perovskite growth limit the exploitation of CH3NH3PbBr3‐based perovskite solar cells. Herein, a post‐treatment is carried out after the initial CH3NH3PbBr3 crystallization based on methylamine gas that drastically enhances the perovskite quality leading to a highly crystalline film with improved average visible transmittance (AVT) close to 56%. Opaque devices showed outstanding results in terms of open‐circuit voltage and power conversion efficiency (PCE) reaching 1.54 V and 9.2%, respectively. These achievements are ascribed to a film with reduced morphological defects and better interface quality and reduced nonradiative pathways. For the first time, the fabrication of semitransparent CH3NH3PbBr3‐based solar cells is demonstrated reaching a maximum PCE equal to 7.6%, an AVT of the full stack device of 52%, and an excellent light stability at maximum‐power point tracking.