Electric Power Conversion Efficiency Research Articles

Theoretical study of the strong piezo-phototronic effect in 2D monochalcogenides for multi-junction solar cells

The piezophototronic effect is a new scientific area that investigates the synergistic interactions of piezoelectric, semiconductor, and photoexcitation features. This effect is seen in crystals lacking inversion symmetry, where applied strain alters electronic transport and provides a way to modify material properties. Monolayer 2D semiconductors, such as transition metal dichalcogenides (TMDCs) and group IV monochalcogenides, have higher piezoelectric coefficients than conventional piezoelectric materials. This study proposes the development of a stable, high-performance multijunction solar cell (MJSC) leveraging the piezo-phototronic effect. The emphasis is on single-type 5-layer 2D monochalcogenides (SnS, SnSe, GeS, and GeSe) with the assistance of strain engineering. Surprisingly, the ultrathin parallel-connected solar cell achieves an electric power conversion efficiency of over 31% when tested under blackbody radiation, surpassing the recognized Shockley–Queisser (S-Q) limit. The piezophototronic effect improves solar cell performance while also addressing voltage mismatch issues. This work introduces a novel approach to developing and manufacturing high-efficiency and robust monolayer multijunction photovoltaic solar cells (MJPSC) based on 2D monochalcogenides.

Impacts of thermal and electric contact resistance on the material design in segmented thermoelectric generators

Segmented thermoelectric generators (STEGs) can exhibit present superior performance than those of the conventional thermoelectric generators. Thermal and electrical contact resistances exist between the thermoelectric material interfaces in each thermoelectric leg. This may significantly hinder performance improvement. In this study, a five-layer STEG with three pairs of thermoelectric (TE) materials was investigated considering the thermal and electrical contact resistances on the material contact surface. The STEG performance under different contact resistances with various combinations of TE materials were analyzed. The relationship between the material sequence and performance indicators under different contact resistances is established by machine learning. Based on the genetic algorithm, for each contact resistance combination, the optimal material sequences were identified by maximizing the electric power and energy conversion efficiency. To reveal the underlying mechanism that determines the heat-to-electrical performance, the total electrical resistance, output voltage, ZT value, and temperature distribution under each optimized scenario were analyzed. The STEG can augment the heat-to-electricity performance only at small contact resistances. A large contact resistance significantly reduces the performance. At an electrical contact resistance of RE = 10–3 K·m2·W−1 and thermal contact resistance of RT = 10–8 Ω·m2, the maximum electric power was reduced to 5.71 mW (90.86 mW without considering the contact resistance). And the maximum energy conversion efficiency is lowered to 2.54% (12.59% without considering the contact resistance).

Impacts of membrane fouling on nanofluidic salinity gradient energy conversion process

Fouling in the membrane interior of engineered large sized charged nanopores can significantly impact the transmembrane ion transportation characteristic. Here impacts of fouling characteristics on the energy conversion performance are investigated. When the fouling located near the low concentration end, the shadowing effect that decreases the effective charged surface area plays a dominant role, which weakens the EDL overlapping degree, and lowers the energy conversion performance. Fouling also brings about blocking effect that narrows the ion transportation channel, and improves ion separation. When the fouling located near the high concentration side, the blocking effect could override the shadowing effect, leading to upgraded energy conversion performance. Due to the coupling of the shadowing effect and blocking effect, the electric power and energy conversion efficiency could overwhelm the performance with no fouling existed. The electric power and energy conversion efficiency under the fouling of r=25 nm are increased by 26.47% and 7.43%, respectively.

Ultrafast-programmable two-dimensional p–n homojunction for high-performance photovoltaics and optoelectronics

Two-dimensional (2D) materials are considered to be promising candidates for constructing revolutionary electronic devices. However, difficulties in controlling the polarity, concentration, and spatial distribution of charge carriers in 2D materials make the construction of 2D p–n junctions rather challenging. Here, we report the successful construction of ultrafast-programmable 2D p–n homojunctions with a semi-floating-gate configuration based on a vertically stacked molybdenum disulfide (MoS2)/hexagonal boron nitride/multilayer graphene van der Waals heterostructure. By partially electrostatically doping the MoS2 channel under different control-gate voltage pulses, three types of 2D homojunctions, including p–n, n+–n, and n–n, can be constructed. The 2D p–n homojunction can be programmed at an ultrafast speed of within 160 ns and exhibits a large rectification ratio of ∼104. Based on a modified Shockley equation, an ideality factor of ∼2.05 is extracted, indicating that the recombination process dominated the transport mechanism. The MoS2 2D p–n homojunction shows a maximum electrical power conversion efficiency of up to 2.66% under a weak light power of 0.61 nW and a high photovoltage responsivity of 5.72 × 109 V W−1. These results indicate that the ultrafast-programmable 2D p–n homojunction has great potential for use in high-performance photovoltaics and optoelectronics.

Thermal mapping of photovoltaic module cooling via radiation-based phase change material matrix: A case study of a large-scale solar farm in Thailand

Under tropical conditions, an increase in solar irradiance abruptly increases the operating temperature of a Photovoltaic (PV) module. This, in turn, deteriorates the electric power conversion efficiency. Several studies have attempted to reduce the PV module temperature using Phase Change Materials (PCM), which is predominant among sensible heat storage materials. The main objective of this study is to examine the thermal variation over the surface of a PV module with a PCM matrix integrated behind the PV module without using physical contact. The contactless PCM matrix spaced 6 mm behind the PV module demonstrates remarkable cooling with controlled heat re-conduction during the off-peak sunshine hours. Our statistical approach to the PV module temperature clearly states that the distance between PV module and ground, wind direction, and stress in thermal dissipation are the key factors affecting thermal variation. Furthermore, the power production capacity of the developed PCM matrix is emphasised in a large-scale solar farm of 15 MWp under Thailand's climatic conditions. Notably, contactless PCM matrix is favourable for cooling the PV module by a maximum of 13.20 °C, compared with the other months and the corresponding power production is 12.05 MW.

Evaluation of mitigation strategies for radioactive fission gases in fluoride-salt-cooled high-temperature reactors

The Fluoride-salt-cooled High-temperature Reactor (FHR) is a promising Generation IV nuclear reactor due to its improved safety design, near atmospheric working pressure, and high electric power conversion efficiency. However, control of radioactive fission gases, such as tritium, is a critical issue in FHRs due to the significantly larger production rate and potentially larger leakage rate of tritium compared to those in Light Water Reactors (LWRs). Therefore, this study proposes two mitigation strategies for tritium in FHRs: Double-Wall Heat eXchanger with a Tritium Carrier (DWHX-TC) option and Single-Wall Heat eXchanger with a Tritium Barrier (SWHX-TB) option. For the DWHX-TC option, two tube surface configurations, i.e., plain and fluted tubes, and four tritium carriers, i.e., helium, FLiBe, FLiNaK, and KF-ZrF4, are initially considered, among which the best tube configuration and promising tritium carrier are then selected and used for design optimization of the DWHX. For the SWHX-TB option, two cases, tritium barriers with and without cracks, are investigated in this study. In addition, the two mitigation strategies are evaluated by an in-house, one-dimensional, coupled HEat and MAss Transfer (HEMAT) code developed to predict the leakage rate of tritium in nuclear systems. Our analysis shows that (1) a double-wall configuration using fluted tubes as both the inner and outer tubes is better than other double-wall configurations investigated; (2) helium, as a tritium carrier, is superior to other candidates, including FLiBe, FLiNaK, and KF-ZrF4; (3) the leakage rate of tritium (into the atmosphere) is reduced from 3400 Ci/day, taking the Advanced High-Temperature Reactor (AHTR) as a reference, to 4.0 Ci/day for an optimum design of the DWHX-TC option using helium as the tritium carrier and 1.7 Ci/day for an optimum design of the SWHX-TB option using 30-µm thick silicon carbide (SiC) as the tritium barrier (no cracks); and (4) potential cracks in tritium barriers may significantly deteriorate mass transfer performance of the SWHX-TB option. For example, a cracking rate of 0.1% leads to an increase of 694.1% in the leakage rate under the conditions investigated.

Minimizing Scaling Losses in High-Performance Quantum Dot Luminescent Solar Concentrators for Large-Area Solar Windows.

While luminescent solar concentrators (LSCs) have been researched for several decades, there is still a lack of commercially available systems, mostly due to scalability, performance, aesthetics, or some combination of these challenges. These obstacles can be overcome by the systematic optimization of a laminated glass LSC design, demonstrated herein. In particular, we first show that it is possible to improve optical and electrical efficiencies of an LSC by fine-tuned optimization of the constituent fluorophore-containing interlayer resin. Further still, an increased understanding of commercially available solar cells allows us to establish a direct correlation between the device's optical and electrical efficiency. Next, optical characterization of LSCs of varying sizes allows us to elucidate the main loss mechanisms in our LSCs, as well as ways to mitigate them. Altogether these optimization steps create opportunities for high-performance multi-interlayer LSC devices with demonstrated electrical power conversion efficiency as high as 1.1% to 4.9% at visual light transmission of 74% to 5%. Furthermore, careful examination of different blue-color (red-band absorbing) dyes provides a path for color-tunability of LSC windows toward neutral regimes. Design iterations of multiple device form factors enabled a color-neutral prototype without significant performance losses by separating color-neutralizing and LSC layers into different panes of an insulated glass unit. This work demonstrates the importance of LSC design optimization in achieving high-performance solar window technology with commercially acceptable aesthetics.

A Modified Hexagonal Pyramidal InP nanowire Solar Cell structure for Efficiency Improvement: Geometrical Optimisation and Device Analysis

Vertically stacked nanostructure arrays are considered as promising candidates for photovoltaic (PV) applications. High absorption and excellent carrier collection efficiency along the axial direction with reductions inreflection and transmission losses have contributed significantly to increasing the efficiency of nanostructure-based InP solar cells (SCs). We investigated the optical and electrical behaviour of three distinct InP nanostructure geometries in this paper: hexagonal nanowire (HNW) SC, hexagonal nanopyramid (HNP) SC, and our proposed Hybrid hexagonal pyramidal nanowire (HHPNW) SC. The optimisation of the geometrical parameters of InP nanostructures grown on an InP substrate, such as diameter (D), period (p), and filling ratio (FR), offers a wide range of variations of the optical and device characteristics as a function of structural morphology. Finite Difference Time Domain (FDTD) simulation of HNW, HNP, and HHPNW structures reveals that our proposed HHPNW SC has a higher generation rate, better absorption, and higher optical short circuit current density (Jsc) of 34.2 mA/cm2 than the HNW (32.5 mA/cm2) and HNP (32.86 mA/cm2). The generation rate profile of all optimised nanostructures is transferred to Lumerical's Device Charge Solver module to investigate the electrical analysis in terms of PV parameters namely electrical Jsc, open-circuit voltage (Voc), Fill Factor (FF), and Power conversion efficiency (PCE). In the electrical analysis, we performed a comparative analysis of the p-n junction and p-i-n junction for all three structures under consideration, and it was observed that our proposed structure, InP HHPNW, outperforms the InP HNW and InP HNP with a conversion efficiency of 19.15 % and 23% for p-n and p-i-n junction, respectively.

45-nm CdS QDs photoluminescent filter for photovoltaic conversionefficiency recovery

Different energy loss mechanisms have restricted the breakthroughs in concentrated photovoltaic/thermal (CPVT) hybrid solar systems that use photoluminescent filters. Re?ected and transmitted light, emission spectrum, nonideal absorption, Stokes shift (proportional to $f_1 f_2$), overlapping absorption, and scattering of light are mechanisms in photoluminescent filters that restrict optical efficiency to below theoretical limits. In addition, increases in temperature by light concentration affect the operation of photovoltaic cells and photoluminescent filters because of an increase in molecular motion and collisions that consequently lead to energy loss. Meanwhile, nanocrystals or quantum dots (QDs) from groups II VI hold electrical, optical, chemical, and physical properties that can be used to mitigate the aforementioned limitations. In this study, cadmium sulfide QDs with a diameter of 45 nm and absorption and photoluminescent spectra centered at 480 and 600 nm, respectively, were deposited in a soda-lima glass to obtain a 200-nm-thick film photoluminescent filter. The photoluminescent filter was matched to a silicon solar cell and used as an electrical power efficiency recovery filter in a hybrid CPVT solar system. A recovery of electrical power conversion efficiency higher than 3.1\% at temperatures greater than 100$^{\circ}$C was theoretically predicted and practically confirmed. A predicted trend of increases in recovered electrical power parameters as temperature increases was also verified.

Impacts of transmembrane pH gradient on nanofluidic salinity gradient energy conversion

Solution pH can impact the nanochannel surface charge density, thus, to regulate the transmembrane ion transportation. Here, the performance of nanofluidic salinity gradient energy conversion is investigated, where the solution pH at the high/low concentration side varies separately, rendering asymmetric pH configurations. Results reveal that the solution pH at the low concentration side (pHL) exhibits a significant impact on the salinity gradient energy conversion. When pHL < Isoelectric Point (IEP), the energy conversion indicators are most stable under various solution pH at the high concentration side (pHH). The surface charge density of the nanochannel at the low concentration end determines the transmembrane ion transportation characteristics, dominating the energy conversion performance. The energy conversion performance via nanochannels of different lengths under asymmetric pH configurations is also studied. There exists optimal nanochannel length corresponding to the maximum electric power, which differs under various pH configurations. For longer nanochannels, the ion concentration polarization effect is weakened, allowing for a more effective energy extraction performance via pH-adjusted salinity gradients. At the length of 2000 nm, the electric power and energy conversion efficiency under the co-direction configuration is 78% and 97.9%, respectively, larger than those under the reverse direction configuration.

Inkjet-printed indium sulfide buffer layer for Cu(In,Ga)(S,Se)2 thin film solar cells

We report an environmentally friendly inkjet-printed indium sulfide (In2S3) buffer layer using benign chemistry and processing conditions. A pre-synthesized indium-thiourea compound is dissolved in a mixture of water and ethanol, inkjet printed on a Cu(In,Ga)(S,Se)2 absorber and annealed in air. The buffer layer shows a β-In2S3 structure with few organic impurities and band gap in the range of 2.3 eV. An ultraviolet ozone treatment applied to the surface of the absorber prior to inkjet printing of the precursor is used to improve the wettability of the ink and therefore the surface coverage of the buffer on the absorber layer. The device with a fully covering In2S3 layer shows better open circuit voltage and fill factor than the device with a partially covering In2S3 layer. The best In2S3 device showed a light to electric power conversion efficiency similar to the reference cadmium sulfide buffer layer device. Good wettability conditions are therefore essential for higher efficiency solar cells when the buffer layer is inkjet-printed.

Segmental material design in thermoelectric devices to boost heat-to-electricity performance

In this study, a seven-layer segmented thermoelectric generator (STEG) is presented with four pairs of TE materials imposed on each semiconductor leg. Firstly, the performance of the STEG with every possible combination (16384 material sequences) of the leg materials for either leg is analyzed when the other leg is equipped with selected material. Machine learning is further employed to reveal the relationship of the electric power and the energy conversion efficiency with the leg material sequences via the ensemble-based regression model whose hyper-parameters are adjusted by the Bayesian optimization. The criteria of maximum output power and maximum energy conversion efficiency are employed to identify the optimal material sequences for each semiconductor leg, thus the overall optimal material sequences. Comparing to the traditional TEG, when operating between 600 K and 293 K, the electric power and energy conversion efficiency of STEG is 184.1 mW and 16.7%, which presents enhancement of 86.14% and 31.19%, respectively. Counterintuitively, the optimal sequence does not arrange in strict conformity with ZT value which has never been reported in the previous studies. The underling mechanisms are revealed via analyzing the temperature distribution, electric resistance, ZT value and voltage of each layers. The results in this study contributes to the rational design and fabrication of satisfied STEGs.

(Plenary) Integrate to Extend the Reach of Solid Oxide Fuel Cells

Solid Oxide Fuel Cells (SOFCs) offer the potential for compelling thermo-economic value propositions in wide range of stationary and transportation applications through their potential for high conversion efficiency and their inherent fuel flexibility. Furthermore, many of the core SOFC materials, component, and system technologies have tremendous potential in electrolysis applications where fuels or chemicals could be produced using renewable electricity. However, to date, the wide-spread commercialization of SOFC/SOEC systems has been hampered by their high cost and durability challenges.Fortunately, high temperature solid oxide-based energy conversion systems are well suited for integration with thermal-mechanical energy conversion systems in configurations that offer the potential for significant cost and thermodynamic performance synergies. Specifically, their integration with gas turbines or internal combustion engines offers the potential for ultra-high (>70%) efficiency at an attractive manufacturing cost (<$1/W). In these hybrid systems, engines or turbines are used to convert stack waste exergy to additional useful work resulting in higher overall efficiency and lower power-specific cost (e.g., $/kW) compared to SOFC-only systems.Furthermore, in the case of SOFC and gas turbine hybrid systems, the SOFC stacks are typically located downstream of the gas turbine compressor and are at elevated pressure—enabling increased Nernst potential and decreased overpotentials and thereby higher power density at constant voltage. This benefit translates into a significant power-specific stack cost reduction. Additionally, the gas turbine compressor and recuperator may serve as the SOFC stack blower and recuperator—yielding further cost synergies via the elimination of duplicative balance of plant components.In 2017, ARPA-E launched the INTEGRATE program to develop hybrid system concepts and enabling component technologies that if realized would result in 100kW-scale distributed generation systems with >70% fuel to electricity conversion efficiencies and system manufacturing costs of <$1/W. In the initial two-year Phase I portion of the program, nine teams developed a suite of hybrid system concepts. Given these concepts, the teams then proceeded to develop 1) durable SOFC stacks that are capable of operating at high (~4 bar) pressure, 2) high temperature (>600 °C) and low-cost heat exchangers, and 3) innovative control system approaches. In 2019, three of the original nine teams were selected to design, build and demonstrate 100kW-scale systems by 2023.In the interest of focusing limited financial resources on foundational development risks, while avoiding the weight, volume, and fuel flexibility challenges associated with transportation applications and mitigating the financial risks associated with adopting new technologies at utility (e.g., >100MW) scale, natural gas fueled distributed generation (DG) systems were selected as the initial INTEGRATE application target. These DG systems would offer a fuel to electric power conversion efficiency that is roughly double that of the fossil fueled portion of the US electric grid. Furthermore, as renewable fuels such as hydrogen, ammonia, and bio- or electro- derived hydrocarbons (e.g., renewable natural gas or synthetic kerosene) become available, these systems would be capable of operating on them with relatively minor fuel processing system adjustments.Moving beyond stationary DG applications, SOFC hybrid systems can leverage their fuel flexibility in the pursuit of a decarbonized of long-distance transportation sector—if the systems can be made both light and small enough. To this end, ARPA-E recently launched three programs that have taken on the challenge of developing ultra-efficient, yet compact and light weight carbon-neutral electrified propulsion systems for commercial aviation.One of these programs is focused on carbon-neutral fuel to electric power conversion sub-systems—Range Extenders for Electric Aviation with Low Carbon and High Efficiency (REEACH). In the two-year Phase 1 of this program, six of nine selected teams will develop SOFC/gas turbine/battery hybrid systems that are fueled with renewable natural gas or synthetic kerosene. Phase 1 focuses on system conceptual design and fuel conversion component risk reduction, while full system design and prototype demonstration of a sub-scale fuel-to-electric power conversion device using a carbon-neutral liquid fuel is planned for Phase 2.If the REEACH-envisioned systems are successfully developed, they would enable economically attractive all-electric commercial aircraft up to a narrow body airframe with dramatically reduced (ideally zero) net carbon emissions. Furthermore, INTEGRATE/REEACH hybrid system technologies would also have attractive value propositions in maritime, rail, or heavy-duty vehicle applications.

Opto-electronic properties and solar cell efficiency modelling of Cu2ZnXS4 (X = Sn, Ge, Si) kesterites

In this work, first-principles calculations of Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4 are performed to highlight the impact of the cationic substitution on the structural, electronic and optical properties of kesterite compounds. Direct bandgaps are reported with values of 1.32, 1.89 and 3.06 eV respectively for Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4 and absorption coefficients of the order of 104 cm−1 are obtained, indicating the applicability of these materials as absorber layer for solar cell applications. In the second part of this study, ab initio results are used as input data to model the electrical power conversion efficiency of kesterite-based solar cells. In that perspective, we used an improved version of the Shockley–Queisser model including non-radiative recombination via an external parameter defined as the internal quantum efficiency. Based on predicted optimal absorber layer thicknesses, the variation of the solar cell maximal efficiency is studied as a function of the non-radiative recombination rate. Maximal efficiencies of 25.71%, 19.85% and 3.10% are reported respectively for Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4 for vanishing non-radiative recombination rate. Using an internal quantum efficiency value providing experimentally comparable values, cell efficiencies of 15.88%, 14.98% and 2.66% are reported respectively for Cu2ZnSnS4, Cu2ZnGeS4 and Cu2ZnSiS4. We confirm the suitability of Cu2ZnSnS4 in single junction solar cells, with a possible efficiency improvement of nearly 10% enabled through the reduction of the non-radiative recombination rate. In addition, Cu2ZnGeS4 appears to be an interesting candidate as top cell absorber layer for tandem approaches whereas Cu2ZnSiS4 might be interesting for transparent photovoltaic windows.

Significantly Enhanced Performance of Nanofluidic Osmotic Power Generation by Slipping Surfaces of Nanopores

High-performance osmotic energy conversion (OEC) with a perm-selective porous membrane requires both high ionic selectivity and permeability simultaneously. Here hydrodynamic slip is considered on the surfaces of nanopores to break the trade-off between ionic selectivity and permeability, because it decreases the viscous friction at solid–liquid interfaces which can promote ionic diffusion during OEC. Taking advantage of simulations, influences from individual slipping surfaces on the OEC performance have been investigated, i.e., the slipping inner surface (surfaceinner) and exterior surfaces on the low- and high-concentration sides (surfaceL and surfaceH). Results show that the slipping surfaceL is crucial for high-performance OEC. For nanopores with various lengths, the slipping surfaceL simultaneously increases both ionic permeability and selectivity of nanopores, which results in both significantly enhanced electric power and energy conversion efficiency. For nanopores longer than 30 nm, the slipping surfaceinner plays a dominant role in the increase of electric power, which induces a considerable decrease in energy conversion efficiency due to enhanced transport of both cations and anions. Considering the difficulty in hydrodynamic slip modification to the surfaceinner of nanopores, the surface modification to the surfaceL may be a better choice to achieve high-performance OEC. Our results provide feasible guidance to the design of porous membranes for high-performance osmotic energy harvesting.

Investigating anode off-gas under spark-ignition combustion for SOFC-ICE hybrid systems

Solid oxide fuel cell – internal combustion engine (SOFC-ICE) hybrid systems are an attractive solution for electricity generation. The system can achieve up to 70% theoretical electric power conversion efficiency through energy cascading enabled by utilizing the anode off-gas from the SOFC as the fuel source for the ICE. Experimental investigations were conducted with a single cylinder Cooperative Fuel Research (CFR) engine by altering fuel-air equivalence ratio (ϕ), and compression ratio (CR) to study the engine load, combustion characteristics, and emissions levels of dry SOFC anode off-gas consisting of 33.9% H2, 15.6% CO, and 50.5% CO2. The combustion efficiency of the anode off-gas was directly evaluated by measuring the engine-out CO emissions. The highest net-indicated fuel conversion efficiency of 31.3% occurred at ϕ = 0.90 and CR = 13:1. These results demonstrate that the anode off-gas can be successfully oxidized using a spark ignition combustion mode. The fuel conversion efficiency of the anode tail gas is expected to further increase in a more modern engine architecture that can achieve increased burn rates in comparison to the CFR engine. NOx emissions from the combustion of anode off-gas were minimal as the cylinder peak temperatures never exceeded 1800 K. This experimental study ultimately demonstrates the viability of an ICE to operate using an anode off-gas, thus creating a complementary role for an ICE to be paired with a SOFC in a hybrid power generation plant.

Synergy analysis for ion selectivity in nanofluidic salinity gradient energy harvesting

For salinity gradient energy harvesting, membrane ion selectivity plays an important role, which is often qualitatively analysed via the electric double layer (EDL) overlapping degree in conventional studies. However, the degree of EDL overlapping is hard to be quantitatively evaluated. Here, we systematically analyze the synergy relations between physical vectors that determining the energy conversion process to quantitatively illustrate the EDL overlapping degree and ion selectivity. Three synergy angles are proposed to describe the synergy relations between the ion diffusion and the electrostatic migration driven forces. A synergy degree parameter is further defined, which could offer a quantitative way to analyze the cation transference number under different concentration ratios, channel length, and asymmetric channel geometries. In addition, an alternative way to use large size nanochannels to efficiently harvest the salinity gradient energy is developed by employing nanowire blockers. The inserted nanowire blocker can significantly enlarge the synergy degree parameter, thus to enhance the ion selectivity, upgrade the membrane potential, and bring a significant augment on the electric power and energy conversion efficiency. This study offers a novel insight into quantitatively analyzing the ion selectivity and paves an alternative way for efficiently salinity gradient energy harvesting via large size nanochannels.

Synergistic Effect of Fluorinated Passivator and Hole Transport Dopant Enables Stable Perovskite Solar Cells with an Efficiency Near 24%

Long-term durability is critically important for the commercialization of perovskite solar cells (PSCs). The ionic character of the perovskite and the hydrophilicity of commonly used additives for the hole-transporting layer (HTL), such as lithium bis(trifluoromethanesulfonyl)imide (Li-TFSI) and tert-butylpyridine (tBP), render PSCs prone to moisture attack, compromising their long-term stability. Here we introduce a trifluoromethylation strategy to overcome this drawback and to boost the PSC's solar to electric power conversion efficiency (PCE). We employ 4-(trifluoromethyl)benzylammonium iodide (TFMBAI) as an amphiphilic modifier for interfacial defect mitigation and 4-(trifluoromethyl)pyridine (TFP) as an additive to enhance the HTL's hydrophobicity. Surface treatment of the triple-cation perovskite with TFMBAI largely suppressed the nonradiative charge carrier recombination, boosting the PCE from 20.9% to 23.9% and suppressing hysteresis, while adding TFP to the HTL enhanced the PCS's resistance to moisture while maintaining its high PCE. Taking advantage of the synergistic effects resulting from the combination of both fluoromethylated modifiers, we realize TFMBAI/TFP-based highly efficient PSCs with excellent operational stability and resistance to moisture, retaining over 96% of their initial efficiency after 500 h maximum power point tracking (MPPT) under simulated 1 sun irradiation and 97% of their initial efficiency after 1100 h of exposure under ambient conditions to a relative humidity of 60-70%.

Origin of a large difference of power conversion efficiency between the hexagonal LuMnO3 and the hexagonal LuFeO3 ferroelectric photovoltaics

Hexagonal LuMnO3 (h-LMO) and LuFeO3 (h-LFO) compounds, in their ferroelectric phases (space group P63cm), are promising ferroelectric photovoltaic materials for converting sunlight into electricity. However, the recent experimental studies demonstrate that the h-LMO exhibits much higher solar to electric power conversion efficiency (PCE) than the h-LFO. In this study, we explain the origin of this difference, basing our analysis on the electronic structure of both compounds, determined from the first-principles calculations at the density functional theory level. Our results demonstrate that the h-LMO PCE is higher than the h-LFO PCE because of the two facts: (1) the effective mass of the photogenerated charges in the h-LFO is larger than in the h-LMO, (2) the binding energy of the photogenerated electron-hole pairs (excitons) is higher in the h-LFO than in the h-LFO. We also report a high anisotropy of the electronic photocurrent in both compounds: due to much larger electron effective mass along the c-axis direction, the photocurrent flow along any direction within the hexagonal basal plane is much more efficient.

Large-Area Transparent 'Quantum Dot Glass' for Building Integrated Photovoltaics

A concept of transparent “Quantum Dot Glass” (TQDG) is proposed for a combination of quantum dot (QD) based glass luminescent solar concentrator (LSC) and its edge-attached solar cells, as a type of transparent photovoltaics (TPV) for building-integrated photovoltaics (BIPV). Different from conventional LSCs, which typically serve as pure optical devices, TQDGs have to fulfill requirements both as power-generating components and building envelop construction materials. In this work, we demonstrate large-area (400 cm2) TQDGs based on environmentally benign silicon QDs in a triplex glass configuration. Balanced photovoltaic performance and aesthetic quality of the TQDGs were achieved by optimization of Si QDs/polymer interlayer thickness and QD loading in the devices. As a result, an overall electrical power conversion efficiency (PCE) of 1.57% was obtained with back-reflection for a highly transparent TQDG (average visible transmittance of 84%, with color rendering index of 94 and low haze ≤ 3%), contributing to a high light utilization efficiency (LUE) of 1.3%, which is among the top of reported TPVs based on LSC technology with similar size. Most importantly, these TQDGs are shown to have better thermal and sound insulation property compared to normal float glass, as well as improved mechanical performance and safety, which significantly pushes the TPV technology towards practical building integration and construction. TQDGs simultaneously exhibiting favorable photovoltaic, aesthetic and building-envelope characteristics, can serve as a multifunctional material for the realization of nearly zero-energy building concept.