Showing papers on "Energy conversion efficiency published in 2011"
TL;DR: Perovskite QD-sensitized 3.6 μm-thick TiO(2) film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm(-2)), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.
Abstract: Highly efficient quantum-dot-sensitized solar cell is fabricated using ca. 2–3 nm sized perovskite (CH3NH3)PbI3 nanocrystal. Spin-coating of the equimolar mixture of CH3NH3I and PbI2 in γ-butyrolactone solution (perovskite precursor solution) leads to (CH3NH3)PbI3 quantum dots (QDs) on nanocrystalline TiO2 surface. By electrochemical junction with iodide/iodine based redox electrolyte, perovskite QD-sensitized 3.6 μm-thick TiO2 film shows maximum external quantum efficiency (EQE) of 78.6% at 530 nm and solar-to-electrical conversion efficiency of 6.54% at AM 1.5G 1 sun intensity (100 mW cm−2), which is by far the highest efficiency among the reported inorganic quantum dot sensitizers.
2,781 citations
TL;DR: A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap and a deep highest occupied molecular orbital energy level.
Abstract: A new alternating copolymer of dithienosilole and thienopyrrole-4,6-dione (PDTSTPD) possesses both a low optical bandgap (1.73 eV) and a deep highest occupied molecular orbital energy level (5.57 eV). The introduction of branched alkyl chains to the dithienosilole unit was found to be critical for the improvement of the polymer solubility. When blended with PC71BM, PDTSTPD exhibited a power conversion efficiency of 7.3% on the photovoltaic devices with an active area of 1 cm2.
1,028 citations
TL;DR: A strong composition gradient in the absorber layer is identified as the main reason for inferior performance and it is shown that, by adjusting it appropriately, very high efficiencies can be obtained.
Abstract: Solar cells based on polycrystalline Cu(In,Ga)Se(2) absorber layers have yielded the highest conversion efficiency among all thin-film technologies, and the use of flexible polymer films as substrates offers several advantages in lowering manufacturing costs. However, given that conversion efficiency is crucial for cost-competitiveness, it is necessary to develop devices on flexible substrates that perform as well as those obtained on rigid substrates. Such comparable performance has not previously been achieved, primarily because polymer films require much lower substrate temperatures during absorber deposition, generally resulting in much lower efficiencies. Here we identify a strong composition gradient in the absorber layer as the main reason for inferior performance and show that, by adjusting it appropriately, very high efficiencies can be obtained. This implies that future manufacturing of highly efficient flexible solar cells could lower the cost of solar electricity and thus become a significant branch of the photovoltaic industry.
810 citations
TL;DR: The use of molybdenum oxide as the anode interfacial layer in conventional bulk heterojunction polymer solar cells leads to an improved power conversion efficiency and also dramatically increases the device stability, indicating that the engineering of improved anode interface materials is an important method by which to fabricate efficient and stable polymer cells.
Abstract: The use of molybdenum oxide as the anode interfacial layer in conventional bulk heterojunction polymer solar cells leads to an improved power conversion efficiency and also dramatically increases the device stability. This indicates that the engineering of improved anode interface materials is an important method by which to fabricate efficient and stable polymer solar cells.
612 citations
TL;DR: In this paper, a novel concept "D-A-π-A" organic sensitizer instead of traditional D-π -A ones is proposed, and the incorporated low bandgap, strong electron-withdrawing unit of benzothiadiazole shows several favorable characteristics.
Abstract: A novel concept “D-A-π-A” organic sensitizer instead of traditional D-π-A ones is proposed. Remarkably, the incorporated low bandgap, strong electron-withdrawing unit of benzothiadiazole shows several favorable characteristics in the areas of light-harvesting and efficiency: i) optimized energy levels, resulting in a large responsive range of wavelengths into NIR region; ii) a very small blue-shift in the absorption peak on thin TiO2 films with respect to that in solution; iii) an improvement in the electron distribution of the donor unit to distinctly increase the photo-stability of synthetic intermediates and final sensitizers. The stability and spectral response of indoline dye-based DSSCs are improved by the strong electron-withdrawing benzothiadizole unit in the conjugation bridge. The incident-photon-conversion efficiency of WS-2 reaches nearly 850 nm with a power conversion efficiency as high as 8.7% in liquid electrolyte and 6.6% in ionic-liquid electrolyte.
610 citations
TL;DR: In this paper, the authors describe the development status of high-efficiency heterojunction with intrinsic thin-layer (HIT) solar cells at SANYO Electric, and they have achieved a quite high open circuit voltage (Voc) of 743mV, and a high conversion efficiency of 22.8% using only a 98-μm-thick substrate.
435 citations
TL;DR: CdS quantum dots were bound onto crystalline P3HT nanowires through solvent-assisted grafting and ligand exchange, leading to controlled organic-inorganic phase separation and an improved maximum power conversion efficiency of 4.1% under AM 1.5 solar illumination.
Abstract: Quantum dots show great promise for fabrication of hybrid bulk heterojunction solar cells with enhanced power conversion efficiency, yet controlling the morphology and interface structure on the nanometer length scale is challenging. Here, we demonstrate quantum dot-based hybrid solar cells with improved electronic interaction between donor and acceptor components, resulting in significant improvement in short-circuit current and open-circuit voltage. CdS quantum dots were bound onto crystalline P3HT nanowires through solvent-assisted grafting and ligand exchange, leading to controlled organic–inorganic phase separation and an improved maximum power conversion efficiency of 4.1% under AM 1.5 solar illumination. Our approach can be applied to a wide range of quantum dots and polymer hybrids and is compatible with solution processing, thereby offering a general scheme for improving the efficiency of nanocrystal hybrid solar cells.
435 citations
Proceedings Article•
15 Jun 2011TL;DR: A 0.35µm CMOS energy processor with multiple inputs from solar, thermal and vibration energy sources is presented and a novel low power maximum power point tracking (MPPT) scheme with 95% tracking efficiency is introduced.
Abstract: A 0.35µm CMOS energy processor with multiple inputs from solar, thermal and vibration energy sources is presented. Dual-path architecture for energy harvesting is proposed that has up to 13% higher conversion efficiency compared to the conventional two stage storage-regulation architecture. To minimize the cost and form factor, a single inductor has been time shared for all converters. A novel low power maximum power point tracking (MPPT) scheme with 95% tracking efficiency is also introduced.
428 citations
19 Jun 2011
TL;DR: Alta Devices, Inc. as discussed by the authors fabricated a thin-film GaAs device on a flexible substrate with an independently-confirmed solar energy conversion efficiency of 27.6%, under AM1.5G solar illumination at 1 sun intensity.
Abstract: Alta Devices, Inc. has fabricated a thin-film GaAs device on a flexible substrate with an independently-confirmed solar energy conversion efficiency of 27.6%, under AM1.5G solar illumination at 1 sun intensity. This represents a new record for single-junction devices under non-concentrated sunlight. This surpasses the previous record, for conversion efficiency of a single-junction device under non-concentrated light, by more than 1%. This is due largely to the high open-circuit voltage (V oc ) of this device. The high V oc results from precise control of the dark current. The fact that this record result has been achieved with a thin-film shows that, for GaAs material systems, the majority of the growth substrate is not needed for device performance. This allows one to consider amortizing the potentially high cost of a GaAs growth substrate by growing a thin-film, lifting it off, and reusing the same substrate multiple times. This technology therefore has the potential to be a novel high-performance, thin-film option for terrestrial photovoltaics.
426 citations
TL;DR: Selective photoreduction of CO(2) to HCOO(-) was achieved in aqueous media, in which H( 2)O was used as both an electron donor and a proton source, and the so-called Z-scheme (or two-step photoexcitation) system operated with no external electrical bias.
Abstract: Photoelectrochemical reduction of CO2 to HCOO– (formate) over p-type InP/Ru complex polymer hybrid photocatalyst was highly enhanced by introducing an anchoring complex into the polymer By functionally combining the hybrid photocatalyst with TiO2 for water oxidation, selective photoreduction of CO2 to HCOO− was achieved in aqueous media, in which H2O was used as both an electron donor and a proton source The so-called Z-scheme (or two-step photoexcitation) system operated with no external electrical bias The selectivity for HCOO− production was >70%, and the conversion efficiency of solar energy to chemical energy was 003–004%
423 citations
TL;DR: In this paper, a colloidal quantum-dot solar cell with two junctions, each designed to absorb and convert different spectral bands of light within the solar spectrum, is presented.
Abstract: Researchers report a colloidal quantum-dot solar cell that features two junctions, each designed to absorb and convert different spectral bands of light within the solar spectrum. The device offers a power conversion efficiency of 4.2% and an open circuit voltage of 1.06 V.
TL;DR: PBB3 showed a long-lived excitonic state and the slowest electron transfer dynamics of the series of polymers, as well as the fastest recombination rate of the charge-separated (CS) species, indicating that electrons and holes are more tightly bound in these species.
Abstract: A new low band gap copolymer PBB3 containing [6,6′]bi[thieno[3,4-b]thiophenyl]-2,2′-dicarboxylic acid bis-(2-butyloctyl) ester (BTT) and 4,8-bis(2-butyloctyl)benzo[1,2-b:4,5-b′]dithiophene (BDT) units was synthesized and tested for solar cell efficiency. PBB3 showed a broad absorbance in the near-IR region with a substantially red-shifted (by more than 100 nm) λmax at 790 nm as compared to the PTB series of polymers, which have been previously reported. The PBB3 polymer also showed both a favorable energy level match with PCBM (with a LUMO energy level of −3.29 eV) and a favorable film domain morphology as evidenced by TEM images. Despite these seemingly optimal parameters, a bulk heterojunction (BHJ) photovoltaic device fabricated from a blend of PBB3 and PC71BM showed an overall power conversion efficiency (PCE) of only 2.04% under AM 1.5G/100 mW cm–2. The transient absorption spectra of PBB3 showed the absence of cationic and pseudo charge transfer states that were observed previously in the PTB series...
TL;DR: Transient photovoltage and photocurrent decay measurements showed that the enhanced performance achieved with C220 partially stems from the high charge collection efficiency over a wide potential range.
Abstract: The high molar absorption coefficient organic D-pi-A dye C220 exhibits more than 6% certified electric power conversion efficiency at AM 1.5G solar irradiation (100 mW cm(-2)) in a solid-state dye sensitized solar cell using 2,2',7,7'-tetrakis(N,N-dimethoxyphenylamine)-9,9'-spirobi-fluorene (Spiro-MeOTAD) as the organic hole transporting material. This contributes to a new record (6.08% by NREL) for this type of sensitized heterojunction photovoltaic device. Efficient charge generation is proved by incident photon-to-current conversion efficiency spectra. Transient photovoltage and photocurrent decay measurements showed that the enhanced performance achieved with C220 partially stems from the high charge collection efficiency over a wide potential range.
TL;DR: In this article, a detailed structure-property relationship study is presented, by identifying those chemical entities in the backbone of conjugated polymers that are responsible for the modification of optoelectronic properties towards high photovoltaic performance.
TL;DR: In this paper, the band gaps of the nanocrystals and the resulting solar cells were controlled by adjusting the Ge/(Ge+Sn) ratio of the precursors of the synthesized precursor.
Abstract: Cu2Zn(Sn1−xGex)S4 nanocrystals have been synthesized via batch reaction in oleylamine with no additional surfactants present. The nanocrystals are knife-coated on molybdenum substrates and then selenized to form a dense layer of Cu2Zn(Sn1−xGex)(S,Se)4, which is then used as the photoabsorbing layer in a thin film solar cell. The band gaps of the nanocrystals and the resulting solar cells are demonstrated to be controlled by adjusting the Ge/(Ge+Sn) ratio of the nanocrystal synthesis precursors. Solar cells fabricated from Cu2ZnGeS4 nanocrystal films yielded a power conversion efficiency of 0.51%. However, Cu2Zn(SnxGe1−x)S4 nanocrystals with a Ge/(Ge+Sn) ratio 0.7 yielded devices with an efficiency of 6.8% when synthesized to be Cu-poor and Zn-rich. This result opens the possibility of forming Ge gradients to direct minority carriers away from high recombination interfaces and significantly improve the device efficiency of CZTSSe-based solar cells.
TL;DR: Hierarchical anatase TiO2 spheres consisting of nanorods and nanoparticles are successfully prepared via a simple acid thermal method using titanium n-butoxide and acetic acid, which will overcome the kinetic and light-scattering limitations of nanoparticles and the surface area limitations of one-dimensional nanostructures, as photoelectrodes for dye-sensitized solar cells as mentioned in this paper.
Abstract: Hierarchical anatase TiO2 spheres consisting of nanorods and nanoparticles are successfully prepared via a simple acid thermal method using titanium n-butoxide and acetic acid, which will overcome the kinetic and light-scattering limitations of nanoparticles and the surface area limitations of one-dimensional nanostructures, as photoelectrodes for dye-sensitized solar cells. The as-prepared and calcined hierarchical spheres were characterized by transmission electron microscopy, scanning electron microscopy and X-ray powder diffraction. The DSSC based on hierarchical TiO2 spheres as the photoelectrode shows a highly efficient power conversion efficiency (10.34%) accompanied by 18.78 mA cm−2 in short-circuit photocurrent density and 826 mV in open-circuit voltage. The great improvements of photocurrent density and power conversion efficiency for hierarchical TiO2 spheres compared to P25 nanoparticle photoelectrodes are mainly attributed to a considerable surface area, a higher light scattering ability, and faster electron transport rates and slower recombination rates for the former.
TL;DR: A new architecture based on surface plasmon excitation within a metal-insulator-metal device that produces power based on spatial confinement of electron excitation through plAsmon absorption is shown.
Abstract: Conversion of light into direct current is important for applications ranging from energy conversion to photodetection, yet often challenging over broad photon frequencies. Here we show a new architecture based on surface plasmon excitation within a metal–insulator–metal device that produces power based on spatial confinement of electron excitation through plasmon absorption. Plasmons excited in the upper metal are absorbed, creating a high concentration of hot electrons which can inject above or tunnel through the thin insulating barrier, producing current. The theoretical power conversion efficiency enhancement achieved can be almost 40 times larger than that of direct illumination while utilizing a broad spectrum of IR to visible wavelengths. Here we present both theoretical estimates of the power conversion efficiency and experimental device measurements, which show clear rectification and power conversion behavior.
TL;DR: It is demonstrated that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO(3) interlayer between the PbS colloidal quantum dot film and the top-contact anode.
Abstract: The ability to engineer interfacial energy offsets in photovoltaic devices is one of the keys to their optimization. Here, we demonstrate that improvements in power conversion efficiency may be attained for ZnO/PbS heterojunction quantum dot photovoltaics through the incorporation of a MoO3 interlayer between the PbS colloidal quantum dot film and the top-contact anode. Through a combination of current–voltage characterization, circuit modeling, Mott–Schottky analysis, and external quantum efficiency measurements performed with bottom- and top-illumination, these enhancements are shown to stem from the elimination of a reverse-bias Schottky diode present at the PbS/anode interface. The incorporation of the high-work-function MoO3 layer pins the Fermi level of the top contact, effectively decoupling the device performance from the work function of the anode and resulting in a high open-circuit voltage (0.59 ± 0.01 V) for a range of different anode materials. Corresponding increases in short-circuit current...
TL;DR: This work demonstrated that the organic-inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%.
Abstract: Silicon nanowire arrays (SiNWs) on a planar silicon wafer can be fabricated by a simple metal-assisted wet chemical etching method. They can offer an excellent light harvesting capability through light scattering and trapping. In this work, we demonstrated that the organic–inorganic solar cell based on hybrid composites of conjugated molecules and SiNWs on a planar substrate yielded an excellent power conversion efficiency (PCE) of 9.70%. The high efficiency was ascribed to two aspects: one was the improvement of the light absorption by SiNWs structure on the planar components; the other was the enhancement of charge extraction efficiency, resulting from the novel top contact by forming a thin organic layer shell around the individual silicon nanowire. On the contrary, the sole planar junction solar cell only exhibited a PCE of 6.01%, due to the lower light trapping capability and the less hole extraction efficiency. It indicated that both the SiNWs structure and the thin organic layer top contact were cr...
TL;DR: An efficient energy harvester for RF-powered sensor networks is presented, based on an improved multi-stage rectifier, which exploits a fully passive threshold self-compensation scheme to overcome the limitation due to the input dead zone.
Abstract: This paper presents an efficient energy harvester for RF-powered sensor networks. The circuit is based on an improved multi-stage rectifier, which exploits a fully passive threshold self-compensation scheme to overcome the limitation due to the input dead zone. A CAD-oriented design methodology is also proposed, which is aimed at maximizing the overall power conversion efficiency of the harvester through an optimum trade-off among matching losses, power reflection and rectifier efficiency. According to the proposed methodology, a 915-MHz harvester comprising an integrated input matching network and a 17-stage self-compensated rectifier has been designed and fabricated in a 90-nm CMOS technology. The rectifier exhibits a remarkably low input power threshold, as it is able to deliver a 1-V dc output voltage to a capacitive load with a very small input power of -24 dBm (4 μW). When driving a 1-MΩ load, the device can supply a 1.2-V output with an input power of -18.8 dBm (13.1 μW). The achieved results exceed the performance of previously reported RF multi-stage rectifiers in standard analog CMOS technology.
TL;DR: In this paper, the dependence of power conversion efficiency on the polymer bandgap and the lowest unoccupied molecular orbital (LUMO) using several typical inorganic acceptors including TiO2, ZnO and CdSe are presented and may provide guidance for the engineering of donor polymers.
Abstract: Polymer–inorganic semiconductor hybrid solar cells have attracted extensive research and attention as a promising approach to achieve cost effective solar energy. Power conversion efficiencies exceeding 3% have been achieved for polymer–inorganic hybrid solar cells. However, these efficiencies are still lower than those of polymer-fullerene solar cells, which have recently reached up to 8.13%. In this article, we review the recent developments including device operation mechanism, cell structures, polymer and inorganic materials, and various approaches to improve cell performance. In addition, the dependence of power conversion efficiency on the polymer bandgap and the lowest unoccupied molecular orbital (LUMO) using several typical inorganic acceptors including TiO2, ZnO and CdSe are presented and may provide guidance for the engineering of donor polymers.
TL;DR: The photoanode is a mesoporous wideband-gap oxide semiconductor film with a high specific surface (typically a thousand times larger than the bulk counterpart) as discussed by the authors.
Abstract: exhibit the highest performance interms of energy conversion efficiency and long term stability,despite the fact that the efficiency remains below 13%because of the intrinsic limitation in charge transport. Thestructure of the photoelectrodes is crucial in determining thefunctional properties of the photoelectrochemical system. Inparticular, the photoanode consists of a mesoporous wide-band-gap oxide semiconductor film with a high specificsurface (typically a thousand times larger than the bulkcounterpart).
TL;DR: 3D-photonic crystal design was utilized to enhance incident photon-to-electron conversion efficiency (IPCE) of WO(3) photoanodes with inverse opal structure and can provide a potential and promising approach to effectively utilize solar energy in visible-light-responsive photoanode.
Abstract: In this study, 3D-photonic crystal design was utilized to enhance incident photon-to-electron conversion efficiency (IPCE) of WO3 photoanodes. Large-area and high-quality WO3 photonic crystal photoanodes with inverse opal structure were prepared. The photonic stop-bands of these WO3 photoanodes were tuned experimentally by variation of the pore size of inverse opal structures. It was found that when the red-edge of the photonic stop-band of WO3 inverse opals overlapped with the WO3 electronic absorption edge at Eg = 2.6–2.8 eV, a maximum of 100% increase in photocurrent intensity was observed under visible light irradiation (λ > 400 nm) in comparison with a disordered porous WO3 photoanode. When the red-edge of the stop-band was tuned well within the electronic absorption range of WO3, noticeable but less amplitude of enhancement in the photocurrent intensity was observed. It was further shown that the spectral region with a selective IPCE enhancement of the WO3 inverse opals exhibited a blue-shift in wav...
TL;DR: In this paper, an n-ZO thin-film layer, prepared with an appropriate thickness by low damage deposition, on high quality Cu2O sheets produced by the thermal oxidization of copper sheets, optimal thickness ranges from 30 to 50 nm.
Abstract: High conversion efficiencies were achieved in low cost n–p heterojunction oxide solar cells with an Al-doped ZnO (AZO)/non-doped ZnO (ZO)/Cu2O structure. This achievement was made possible by the formation of an n-ZO thin-film layer, prepared with an appropriate thickness by low damage deposition, on high quality Cu2O sheets produced by the thermal oxidization of copper sheets: n-ZO thin film optimal thickness ranges from 30 to 50 nm. Photovoltaic characteristics such as an open circuit voltage of 0.69 V, a fill factor of 0.55 and a conversion efficiency of 3.83% were attained under simulated AM1.5G solar illumination.
TL;DR: In this paper, a series-connected dye-sensitized solar cell (DSSC), a solar selective absorber (SSA), and a TE generator were combined to achieve high conversion efficiency.
Abstract: A novel photovoltaic–thermoelectric (PV–TE) hybrid device composed of a series-connected dye-sensitized solar cell (DSSC), a solar selective absorber (SSA) and a TE generator is created. The conversion efficiency of the DSSC was enhanced significantly by using the SSA and TE generator to utilize residual sunlight transmitted through the DSSC. The hybrid device comprising a DSSC as a “top cell” for high-energy photons and an SSA coated TE generator as a “bottom cell” for low-energy photons gave rise to an overall conversion efficiency larger than 13%. Although our hybrid device was not yet optimized but served as proof-of-principle for harvesting electricity from solar light and heat simultaneously with high conversion efficiency by a single device, this study would give some enlightenment for the development of high-performance PV–TE hybrid devices.
TL;DR: A vacuum-deposited organic solar cell employing DTDCTB combined with the electron acceptor C(70) achieved a record-high power conversion efficiency (PCE) of 5.81%.
Abstract: A novel donor–acceptor–acceptor (D–A–A) donor molecule, DTDCTB, in which an electron-donating ditolylaminothienyl moiety and an electron-withdrawing dicyanovinylene moiety are bridged by another electron-accepting 2,1,3-benzothiadiazole block, has been synthesized and characterized. A vacuum-deposited organic solar cell employing DTDCTB combined with the electron acceptor C70 achieved a record-high power conversion efficiency (PCE) of 5.81%. The respectable PCE is attributed to the solar spectral response extending to the near-IR region and the ultracompact absorption dipole stacking of the DTDCTB thin film.
TL;DR: Nanostructured Si eliminates several critical problems with Si photocathodes and dramatically improves a photoelectrochemical (PEC) reaction important to water-splitting in this article.
Abstract: Nanostructured Si eliminates several critical problems with Si photocathodes and dramatically improves a photoelectrochemical (PEC) reaction important to water-splitting Our nanostructured black Si photocathodes improve the H2 production by providing (1) near-ideal anti-reflection that enables the absorption of most incident light and its conversion to photogenerated electrons and (2) extremely high surface area in direct contact with water that reduces the overpotential needed for the PEC hydrogen half-reaction Application of these advances would significantly improve the solar H2 conversion efficiency of an ideal tandem PEC system Finally, the nanostructured Si surface facilitates bubble evolution and therefore reduces the need for surfactants in the electrolyte
TL;DR: An iodine-free dye-sensitized solar cell exhibiting an impressive power conversion efficiency of 7.0% at 100 mW cm(-2) air mass global (AM1.5G) conditions is presented.