Showing papers on "Energy conversion efficiency published in 2016"

Energy-Level Modulation of Small-Molecule Electron Acceptors to Achieve over 12% Efficiency in Polymer Solar Cells

Abstract: Fine energy-level modulations of small-molecule acceptors (SMAs) are realized via subtle chemical modifications on strong electron-withdrawing end-groups. The two new SMAs (IT-M and IT-DM) end-capped by methyl-modified dicycanovinylindan-1-one exhibit upshifted lowest unoccupied molecular orbital (LUMO) levels, and hence higher open-circuit voltages can be observed in the corresponding devices. Finally, a top power conversion efficiency of 12.05% is achieved.

Bandgap-tunable cesium lead halide perovskites with high thermal stability for efficient solar cells

Abstract: Highest reported efficiency cesium lead halide perovskite solar cells are realized by tuning the bandgap and stabilizing the black perovskite phase at lower temperatures. CsPbI2Br is employed in a planar architecture device resulting in 9.8% power conversion efficiency and over 5% stabilized power output. Offering substantially enhanced thermal stability over their organic based counterparts, these results show that all-inorganic perovskites can represent a promising next step for photovoltaic materials.

Scalable water splitting on particulate photocatalyst sheets with a solar-to-hydrogen energy conversion efficiency exceeding 1%

Abstract: Photocatalytic water splitting using semiconductors is attractive for converting solar energy into hydrogen. An efficient and scalable system based on particulate photocatalyst sheets is now shown to exhibit energy conversion efficiency exceeding 1%. Photocatalytic water splitting using particulate semiconductors is a potentially scalable and economically feasible technology for converting solar energy into hydrogen1,2,3. Z-scheme systems based on two-step photoexcitation of a hydrogen evolution photocatalyst (HEP) and an oxygen evolution photocatalyst (OEP) are suited to harvesting of sunlight because semiconductors with either water reduction or oxidation activity can be applied to the water splitting reaction4,5. However, it is challenging to achieve efficient transfer of electrons between HEP and OEP particles6,7. Here, we present photocatalyst sheets based on La- and Rh-codoped SrTiO3 (SrTiO3:La, Rh; ref. 8) and Mo-doped BiVO4 (BiVO4:Mo) powders embedded into a gold (Au) layer. Enhancement of the electron relay by annealing and suppression of undesirable reactions through surface modification allow pure water (pH 6.8) splitting with a solar-to-hydrogen energy conversion efficiency of 1.1% and an apparent quantum yield of over 30% at 419 nm. The photocatalyst sheet design enables efficient and scalable water splitting using particulate semiconductors.

Fast charge separation in a non-fullerene organic solar cell with a small driving force

Abstract: Fast and efficient charge separation is essential to achieve high power conversion efficiency in organic solar cells (OSCs). In state-of-the-art OSCs, this is usually achieved by a significant driv ...

Enhanced electronic properties in mesoporous TiO2 via lithium doping for high-efficiency perovskite solar cells

Abstract: Perovskite solar cells are one of the most promising photovoltaic technologies with their extraordinary progress in efficiency and the simple processes required to produce them. However, the frequent presence of a pronounced hysteresis in the current voltage characteristic of these devices arises concerns on the intrinsic stability of organo-metal halides, challenging the reliability of technology itself. Here, we show that n-doping of mesoporous TiO2 is accomplished by facile post treatment of the films with lithium salts. We demonstrate that the Li-doped TiO2 electrodes exhibit superior electronic properties, by reducing electronic trap states enabling faster electron transport. Perovskite solar cells prepared using the Li-doped films as scaffold to host the CH3NH3PbI3 light harvester produce substantially higher performances compared with undoped electrodes, improving the power conversion efficiency from 17 to over 19% with negligible hysteretic behaviour (lower than 0.3%).

Highly efficient and stable planar perovskite solar cells by solution-processed tin oxide

Abstract: Perovskite solar cells (PSCs) are one of the most promising lab-scale technologies to deliver inexpensive solar electricity. Low-temperature planar PSCs are particularly suited for large-scale manufacturing. Here, we propose a simple, solution-processed technological approach for depositing SnO2 layers. The use of these layers in planar PSCs yields a high stabilized power conversion efficiency close to 21%, exhibiting stable performance under real operating conditions for over 60 hours. In addition, this method yielded remarkable voltages of 1214 mV at a band gap of 1.62 eV (approaching the thermodynamic limit of 1.32 V) confirming the high selectivity of the solution-processed layers. PSCs aged under 1 sun illumination and maximum power point tracking showed a final PCE of 20.7% after ageing and dark storage, which is slightly higher than the original efficiency. This approach represents an advancement in the understanding of the role of electron selective layers on the efficiency and stability of PSCs. Therefore, the newly proposed approach constitutes a simple, scalable method paving the way for industrialization of perovskite solar cells.

All-Polymer Solar Cells Based on Absorption-Complementary Polymer Donor and Acceptor with High Power Conversion Efficiency of 8.27%.

Abstract: High-efficiency all-polymer solar cells with less thickness-dependent behavior are demonstrated by using a low bandgap n-type conjugated polymer N2200 as acceptor and an absorption-complementary difluorobenzotriazole-based medium-bandgap polymer J51 as donor.

High-efficiency robust perovskite solar cells on ultrathin flexible substrates

Abstract: Wide applications of personal consumer electronics have triggered tremendous need for portable power sources featuring light-weight and mechanical flexibility. Perovskite solar cells offer a compelling combination of low-cost and high device performance. Here we demonstrate high-performance planar heterojunction perovskite solar cells constructed on highly flexible and ultrathin silver-mesh/conducting polymer substrates. The device performance is comparable to that of their counterparts on rigid glass/indium tin oxide substrates, reaching a power conversion efficiency of 14.0%, while the specific power (the ratio of power to device weight) reaches 1.96 kW kg(-1), given the fact that the device is constructed on a 57-μm-thick polyethylene terephthalate based substrate. The flexible device also demonstrates excellent robustness against mechanical deformation, retaining >95% of its original efficiency after 5,000 times fully bending. Our results confirmed that perovskite thin films are fully compatible with our flexible substrates, and are thus promising for future applications in flexible and bendable solar cells.

A polymer scaffold for self-healing perovskite solar cells.

Abstract: Advancing of the lead halide perovskite solar cells towards photovoltaic market demands large-scale devices of high-power conversion efficiency, high reproducibility and stability via low-cost fabrication technology, and in particular resistance to humid environment for long-time operation. Here we achieve uniform perovskite film based on a novel polymer-scaffold architecture via a mild-temperature process. These solar cells exhibit efficiency of up to ∼16% with small variation. The unencapsulated devices retain high output for up to 300 h in highly humid environment (70% relative humidity). Moreover, they show strong humidity resistant and self-healing behaviour, recovering rapidly after removing from water vapour. Not only the film can self-heal in this case, but the corresponding devices can present power conversion efficiency recovery after the water vapour is removed. Our work demonstrates the value of cheap, long chain and hygroscopic polymer scaffold in perovskite solar cells towards commercialization. Perovskite solar cells exhibit large conversion efficiencies, but their stability still represents a bottleneck. Here, the authors integrate a hygroscopic polymer scaffold to the perovskite active layer and fabricate efficient and stable devices that recover after being exposed to a humid environment.

Enhanced Efficiency and Stability of Inverted Perovskite Solar Cells Using Highly Crystalline SnO2 Nanocrystals as the Robust Electron-Transporting Layer

Abstract: Highly crystalline SnO2 is demonstrated to serve as a stable and robust electron-transporting layer for high-performance perovskite solar cells. Benefiting from its high crystallinity, the relatively thick SnO2 electron-transporting layer (≈120 nm) provides a respectable electron-transporting property to yield a promising power conversion efficiency (PCE)(18.8%) Over 90% of the initial PCE can be retained after 30 d storage in ambient with ≈70% relative humidity.

Bidirectional conversion between microwave and light via ferromagnetic magnons

Abstract: Coherent conversion of microwave and optical photons in the single quantum level can significantly expand our ability to process signals in various fields. Efficient up-conversion of a feeble signal in the microwave domain to the optical domain will lead to quantum-noise-limited microwave amplifiers. Coherent exchange between optical photons and microwave photons will also be a stepping stone to realize long-distance quantum communication. Here we demonstrate bidirectional and coherent conversion between microwave and light using collective spin excitations in a ferromagnet. The converter consists of two harmonic oscillator modes, a microwave cavity mode and a magnetostatic mode called the Kittel mode, where microwave photons and magnons in the respective modes are strongly coupled and hybridized. An itinerant microwave field and a traveling optical field can be coupled through the hybrid system, where the microwave field is coupled to the hybrid system through the cavity mode, while the optical field addresses the hybrid system through the Kittel mode via Faraday and inverse Faraday effects. The conversion efficiency is theoretically analyzed and experimentally evaluated. The possible schemes for improving the efficiency are also discussed.

Efficient perovskite solar cells by metal ion doping

Abstract: Realizing the theoretical limiting power conversion efficiency (PCE) in perovskite solar cells requires a better understanding and control over the fundamental loss processes occurring in the bulk of the perovskite layer and at the internal semiconductor interfaces in devices. One of the main challenges is to eliminate the presence of charge recombination centres throughout the film which have been observed to be most densely located at regions near the grain boundaries. Here, we introduce aluminium acetylacetonate to the perovskite precursor solution, which improves the crystal quality by reducing the microstrain in the polycrystalline film. At the same time, we achieve a reduction in the non-radiative recombination rate, a remarkable improvement in the photoluminescence quantum efficiency (PLQE) and a reduction in the electronic disorder deduced from an Urbach energy of only 12.6 meV in complete devices. As a result, we demonstrate a PCE of 19.1% with negligible hysteresis in planar heterojunction solar cells comprising all organic p and n-type charge collection layers. Our work shows that an additional level of control of perovskite thin film quality is possible via impurity cation doping, and further demonstrates the continuing importance of improving the electronic quality of the perovskite absorber and the nature of the heterojunctions to further improve the solar cell performance.

Highly efficient quantum dot near-infrared light-emitting diodes

Abstract: Embedding quantum dots in a perovskite matrix yields efficient light emitters. Colloidal quantum dots (CQDs) are emerging as promising materials for constructing infrared sources in view of their tunable luminescence, high quantum efficiency and compatibility with solution processing1. However, CQD films available today suffer from a compromise between luminescence efficiency and charge transport, and this leads to unacceptably high power consumption. Here, we overcome this issue by embedding CQDs in a high-mobility hybrid perovskite matrix. The new composite enhances radiative recombination in the dots by preventing transport-assisted trapping losses; yet does so without increasing the turn-on voltage. Through compositional engineering of the mixed halide matrix, we achieve a record electroluminescence power conversion efficiency of 4.9%. This surpasses the performance of previously reported CQD near-infrared devices two-fold, indicating great potential for this hybrid QD-in-perovskite approach.

Efficient solar-driven water splitting by nanocone BiVO4-perovskite tandem cells.

Abstract: Bismuth vanadate (BiVO4) has been widely regarded as a promising photoanode material for photoelectrochemical (PEC) water splitting because of its low cost, its high stability against photocorrosion, and its relatively narrow band gap of 2.4 eV. However, the achieved performance of the BiVO4 photoanode remains unsatisfactory to date because its short carrier diffusion length restricts the total thickness of the BiVO4 film required for sufficient light absorption. We addressed the issue by deposition of nanoporous Mo-doped BiVO4 (Mo:BiVO4) on an engineered cone-shaped nanostructure, in which the Mo:BiVO4 layer with a larger effective thickness maintains highly efficient charge separation and high light absorption capability, which can be further enhanced by multiple light scattering in the nanocone structure. As a result, the nanocone/Mo:BiVO4/Fe(Ni)OOH photoanode exhibits a high water-splitting photocurrent of 5.82 ± 0.36 mA cm−2 at 1.23 V versus the reversible hydrogen electrode under 1-sun illumination. We also demonstrate that the PEC cell in tandem with a single perovskite solar cell exhibits unassisted water splitting with a solar-to-hydrogen conversion efficiency of up to 6.2%.

Passivation Using Molecular Halides Increases Quantum Dot Solar Cell Performance

Abstract: A solution-based passivation scheme is developed featuring the use of molecular iodine and PbS colloidal quantum dots (CQDs). The improved passivation translates into a longer carrier diffusion length in the solid film. This allows thicker solar-cell devices to be built while preserving efficient charge collection, leading to a certified power conversion efficiency of 9.9%, which is a new record in CQD solar cells.

Boosted output performance of triboelectric nanogenerator via electric double layer effect

Abstract: For existing triboelectric nanogenerators (TENGs), it is important to explore unique methods to further enhance the output power under realistic environments to speed up their commercialization. We report here a practical TENG composed of three layers, in which the key layer, an electric double layer, is inserted between a top layer, made of Al/polydimethylsiloxane, and a bottom layer, made of Al. The efficient charge separation in the middle layer, based on Volta's electrophorus, results from sequential contact configuration of the TENG and direct electrical connection of the middle layer to the earth. A sustainable and enhanced output performance of 1.22 mA and 46.8 mW cm-2 under low frequency of 3 Hz is produced, giving over 16-fold enhancement in output power and corresponding to energy conversion efficiency of 22.4%. Finally, a portable power-supplying system, which provides enough d.c. power for charging a smart watch or phone battery, is also successfully developed.

Rational Strategies for Efficient Perovskite Solar Cells

Abstract: ConspectusA long-standing dream in the large scale application of solar energy conversion is the fabrication of solar cells with high-efficiency and long-term stability at low cost. The realization of such practical goals depends on the architecture, process and key materials because solar cells are typically constructed from multilayer heterostructures of light harvesters, with electron and hole transporting layers as a major component. Recently, inorganic–organic hybrid lead halide perovskites have attracted significant attention as light absorbers for the fabrication of low-cost and high-efficiency solar cells via a solution process. This mainly stems from long-range ambipolar charge transport properties, low exciton binding energies, and suitable band gap tuning by managing the chemical composition. In our pioneering work, a new photovoltaic platform for efficient perovskite solar cells (PSCs) was proposed, which yielded a high power conversion efficiency (PCE) of 12%. The platform consisted of a pill...

Stable Low‐Bandgap Pb–Sn Binary Perovskites for Tandem Solar Cells

Abstract: A low-bandgap (1.33 eV) Sn-based MA0.5 FA0.5 Pb0.75 Sn0.25 I3 perovskite is developed via combined compositional, process, and interfacial engineering. It can deliver a high power conversion efficiency (PCE) of 14.19%. Finally, a four-terminal all-perovskite tandem solar cell is demonstrated by combining this low-bandgap cell with a semitransparent MAPbI3 cell to achieve a high efficiency of 19.08%.

Optoelectronic Properties of (CH3NH3)3Sb2I9 Thin Films for Photovoltaic Applications

Abstract: We present solution-based fabrication and characterization of the lead-free perovskite-related methylammonium antimony iodide (CH3NH3)3Sb2I9 compound. By photothermal deflection spectroscopy (PDS), we determined a peak absorption coefficient α ≈ 105 cm–1 and an optical band gap of 2.14 eV for amorphous films of (CH3NH3)3Sb2I9. Compared to the related Bi compound, the Sb-perovskite shows no exciton peak in its absorption spectrum. The photoluminescence emission (PL) is observed at 1.58 eV, and the Urbach tail energy of this amorphous compound is Eu = 62 meV, indicating a substantial amount of energetic disorder. We fabricate a planar heterojunction solar cell with a (CH3NH3)3Sb2I9 absorber layer that yields a power conversion efficiency of η ≈ 0.5%, already featuring a decent fill factor (FF) of 55% and open-circuit voltage of 890 mV but low photocurrent densities. The result of this basic study on (CH3NH3)3Sb2I9 shows that this compound is a possible starting point for further research into Sb-based lead-...

An Approach to Design Highly Durable Piezoelectric Nanogenerator Based on Self-Poled PVDF/AlO-rGO Flexible Nanocomposite with High Power Density and Energy Conversion Efficiency

Abstract: Till date, fabrication of piezoelectric nanogenerator (PNG) with highly durable, high power density, and high energy conversion efficiency is of great concern. Here a flexible, sensitive, cost effective hybrid piezoelectric nanogenerator (HPNG) developed by integrating flexible steel woven fabric electrodes into poly(vinylidene fluoride) (PVDF)/aluminum oxides decorated reduced graphene oxide (AlO-rGO) nanocomposite film is reported where AlO-rGO acts as nucleating agent for electroactive β-phase formation. The HPNG exhibits reliable energy harvesting performance with high output, fast charging capability, and high durability compared with previously reported PVDF based PNGs. This HPNG is capable for harvesting energy from a variety and easy accessible biomechanical and mechanical energy sources such as, body movements (e.g., hand folding, jogging, heel pressing, and foot striking, etc.) and machine vibration. The HPNG exhibits high output power density and energy conversion efficiency, facilitating direct light on different color of several commercial light-emitting diodes instantly and powers up many portable electronic devices like wrist watch, calculator, speaker, and mobile liquid crystal display (LCD) screen through capacitor charging. More importantly, HPNG retains its performance after long compression cycles (≈158 400), demonstrating great promise as a piezoelectric energy harvester toward practical applications in harvesting biomechanical and mechanical energy for self-powered systems.

An ultra-thin, un-doped NiO hole transporting layer of highly efficient (16.4%) organic–inorganic hybrid perovskite solar cells

Abstract: NiO is a wide band gap p-type oxide semiconductor and has potential for applications in solar energy conversion as a hole-transporting layer (HTL). It also has good optical transparency and high chemical stability, and the capability of aligning the band edges to the perovskite (CH3NH3PbI3) layers. Ultra-thin and un-doped NiO films with much less absorption loss were prepared by atomic layer deposition (ALD) with highly precise control over thickness without any pinholes. Thin enough (5–7.5 nm in thickness) NiO films with the thickness of few time the Debye length (LD = 1–2 nm for NiO) show enough conductivities achieved by overlapping space charge regions. The inverted planar perovskite solar cells with NiO films as HTLs exhibited the highest energy conversion efficiency of 16.40% with high open circuit voltage (1.04 V) and fill factor (0.72) with negligible current–voltage hysteresis.

Polymer Acceptor Based on Double B←N Bridged Bipyridine (BNBP) Unit for High-Efficiency All-Polymer Solar Cells.

Abstract: A novel polymer acceptor based on the double B←N bridged bipyridine building block is reported. All-polymer solar cells based on the new polymer acceptor show a power conversion efficiency of as high as 6.26% at a photon energy loss of only 0.51 eV.

The role of surface passivation for efficient and photostable PbS quantum dot solar cells

Abstract: For any emerging photovoltaic technology to become commercially relevant, both its power conversion efficiency and photostability are key parameters to be fulfilled. Colloidal quantum dot solar cells are a solution-processed, low-cost technology that has reached an efficiency of about 9% by judiciously controlling the surface of the quantum dots to enable surface passivation and tune energy levels. However, the role of the quantum dot surface on the stability of these solar cells has remained elusive. Here we report on highly efficient and photostable quantum dot solar cells with efficiencies of 9.6% (and independently certificated values of 8.7%). As a result of optimized surface passivation and the suppression of hydroxyl ligands—which are found to be detrimental for both efficiency and photostability—the efficiency remains within 80% of its initial value after 1,000 h of continuous illumination at AM1.5G. Our findings provide insights into the role of the quantum dot surface in both the stability and efficiency of quantum dot solar cells. Controlling the surface of quantum dots has enabled higher efficiency in quantum dot solar cells. Now, the role of surface passivation and suppression of hydroxyl ligands in the performance and photostability of cells with an efficiency of 9.6% is unveiled.

UV Degradation and Recovery of Perovskite Solar Cells

Abstract: Although the power conversion efficiency of perovskite solar cells has increased from 3.81% to 22.1% in just 7 years, they still suffer from stability issues, as they degrade upon exposure to moisture, UV light, heat, and bias voltage. We herein examined the degradation of perovskite solar cells in the presence of UV light alone. The cells were exposed to 365 nm UV light for over 1,000 h under inert gas at <0.5 ppm humidity without encapsulation. 1-sun illumination after UV degradation resulted in recovery of the fill factor and power conversion efficiency. Furthermore, during exposure to consecutive UV light, the diminished short circuit current density (Jsc) and EQE continuously restored. 1-sun light soaking induced recovery is considered to be caused by resolving of stacked charges and defect state neutralization. The Jsc and EQE bounce-back phenomenon is attributed to the beneficial effects of PbI2 which is generated by the decomposition of perovskite material.

Constructing Black Titania with Unique Nanocage Structure for Solar Desalination.

Abstract: Solar desalination driven by solar radiation as heat source is freely available, however, hindered by low efficiency. Herein, we first design and synthesize black titania with a unique nanocage structure simultaneously with light trapping effect to enhance light harvesting, well-crystallized interconnected nanograins to accelerate the heat transfer from titania to water and with opening mesopores (4–10 nm) to facilitate the permeation of water vapor. Furthermore, the coated self-floating black titania nanocages film localizes the temperature increase at the water–air interface rather than uniformly heating the bulk of the water, which ultimately results in a solar–thermal conversion efficiency as high as 70.9% under a simulated solar light with an intensity of 1 kW m–2 (1 sun). This finding should inspire new black materials with rationally designed structure for superior solar desalination performance.

Highly Efficient Organic Solar Cells with Improved Vertical Donor–Acceptor Compositional Gradient Via an Inverted Off‐Center Spinning Method

Abstract: A novel, yet simple solution fabrication technique to address the trade-off between photocurrent and fill factor in thick bulk heterojunction organic solar cells is described. The inverted off-center spinning technique promotes a vertical gradient of the donor-acceptor phase-separated morphology, enabling devices with near 100% internal quantum efficiency and a high power conversion efficiency of 10.95%.