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1.
Artigo em Inglês | MEDLINE | ID: mdl-32402191

RESUMO

Efficient and stable electron selective materials compatible with commercial production are essential to the fabrication of dopant-free silicon solar cells. In this work, we report an air-stable TiN (titanium nitride) polycrystalline film, deposited using radio frequency sputtering process, as an electron selective contact in silicon solar cells. TiN films deposited at 300 W and 1.5 mTorr exhibit a low contact resistivity of 2.0 mΩ·cm2. Furthermore, the main factors and mechanisms affecting the carrier selectivity properties are also explored. TiN layers as full area rear electron contacts in n-type silicon solar cells have been successfully implemented, even though TiN film contains some oxygen. This process yields a 17% increment in relative efficiency in comparison with reference devices (n-Si/Al contact). Hence, considering the low thermal budget, scalable technique, and low contact resistivity, the TiN layers can pave the way to fabricate high-efficiency selective contact silicon solar cells with a higher degree of reproducibility.

2.
Opt Lett ; 44(19): 4865-4868, 2019 Oct 01.
Artigo em Inglês | MEDLINE | ID: mdl-31568462

RESUMO

To unlock the full potential of the perovskite solar cell (PSC) photocurrent density and power conversion efficiency, the topic of optical management and design optimization is of absolute importance. Here, we propose a gradient-index optical design of the PSC based on a Gaussian-type front-side glass structure. Numerical simulations clarify a broadband light-harvesting response of the new design, showing that a maximal photocurrent density of 23.35 mA/cm2 may be expected, which is an increase by 1.21 mA/cm2 compared with that of the traditional flat-glass counterpart (22.14 mA/cm2). Comprehensive analysis of the electric field distributions elucidates the light-trapping mechanism. Furthermore, PSCs having the Gaussian index profile display superior optical properties and performance compared to those of the uniform index counterpart under varying conditions of perovskite layer thicknesses and incident angles. The simulation results in this study provide an effective design scheme to promote optical absorption in PSCs.

3.
ACS Appl Mater Interfaces ; 11(40): 36727-36734, 2019 Oct 09.
Artigo em Inglês | MEDLINE | ID: mdl-31525907

RESUMO

Tin oxide (SnO2) is widely used in perovskite solar cells (PSCs) as an electron transport layer (ETL) material. However, its high surface trap density has already become a strong factor limiting PSC development. In this work, phosphoric acid is adopted to eliminate the SnO2 surface dangling bonds to increase electron collection efficiency. The phosphorus mainly exists at the boundaries in the form of chained phosphate groups, bonding with which more than 47.9% of Sn dangling bonds are eliminated. The reduction of surface trap states depresses the electron transport barriers, thus the electron mobility increases about 3 times when the concentration of phosphoric acid is optimized with 7.4 atom % in the SnO2 precursor. Furthermore, the stability of the perovskite layer deposited on the phosphate-passivated SnO2 (P-SnO2) ETL is gradually improved with an increase of the concentration. Due to the higher electron collection efficiency, the P-SnO2 ETLs can dramatically promote the power conversion efficiency (PCE) of the PSCs. As a result, the champion PSC has a PCE of 21.02%. Therefore, it has been proved that this simple method is efficient to improve the quality of ETL for high-performance PSCs.

4.
Nanotechnology ; 30(43): 435202, 2019 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-31304918

RESUMO

AlGaN-based deep ultraviolet (DUV) multiple-quantum-wells (MQWs) incorporating strain-modulated nanostructures are proposed, demonstrating enhanced degree of polarization (DOP) and improved light extraction efficiency (LEE). The influence of Al composition and bi-axial strains on the optical behaviors of the DUV-MQWs were carefully examined. Compared with planar DUV-MQWs, strain-modulated nanostructure patterned MQWs show three times higher photoluminescence and increased DOP from -0.43 to -0.16. Moreover, nanostructure patterned DUV-MQWs under compressive strains further illustrate higher DOP and LEE values than those under tensile strains due to more efficient diffraction of the guided modes of the transverse electric (TE) polarized light. Our work demonstrates, for the first time, that a combination of compressive in-plane strain and surface nanostructure show unambiguous advantages in facilitating TE mode emission, thus have great promises in the design and optimization of highly efficient polarized DUV optoelectronic devices.

5.
Opt Express ; 27(11): 16195-16205, 2019 May 27.
Artigo em Inglês | MEDLINE | ID: mdl-31163803

RESUMO

The optical properties of hexagonal GaN microdisk arrays grown on sapphire substrates by selective area growth (SAG) technique were investigated both experimentally and theoretically. Whispering-gallery-mode (WGM) lasing is observed from various directions of the GaN pyramids collected at room temperature, with the dominant lasing mode being Transverse-Electric (TE) polarized. A relaxation of compressive strain in the lateral overgrown region of the GaN microdisk is illustrated by photoluminescence (PL) mapping and Raman spectroscopy. A strong correlation between the crystalline quality and lasing behavior of the GaN microdisks was also demonstrated.

6.
ACS Nano ; 13(6): 6356-6362, 2019 Jun 25.
Artigo em Inglês | MEDLINE | ID: mdl-31017761

RESUMO

In order to achieve a high performance-to-cost ratio to photovoltaic devices, the development of crystalline silicon (c-Si) solar cells with thinner substrates and simpler fabrication routes is an important step. Thin-film heterojunction solar cells (HSCs) with dopant-free and carrier-selective configurations look like ideal candidates in this respect. Here, we investigated the application of n-type silicon/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HSCs on periodic nanopyramid textured, ultrathin c-Si (∼25 µm) substrates. A fluorine-doped titanium oxide film was used as an electron-selective passivating layer showing excellent interfacial passivation (surface recombination velocity ∼10 cm/s) and contact property (contact resistivity ∼20 mΩ/cm2). A high efficiency of 15.10% was finally realized by optimizing the interfacial recombination and series resistance at both the front and rear sides, showing a promising strategy to fabricate high-performance ultrathin c-Si HSCs with a simple and low-temperature procedure.

7.
Nanotechnology ; 30(19): 195401, 2019 May 10.
Artigo em Inglês | MEDLINE | ID: mdl-30673648

RESUMO

PEDOT: PSS/silicon heterojunction solar cell has recently attracted much attention due to the fact that it can be simply and cost-effectively fabricated. It is crucial to suppress the interfacial recombination rate between silicon (Si) and organic film for improving device efficiency. In this study, we demonstrated a thickness-dependent passivation effect, i.e. the passivation quality over Si substrate was promoted dramatically with increasing the thickness of PEDOT:PSS layer. The effective minority carrier lifetime increased from 32 µs for 50 nm to 360 µs for 200 nm, which corresponds to a change in implied open circuit voltage (V oc-implied) from 545 to 635 mV. Back-junction hybrid solar cells featuring PEDOT:PSS films at rear side were designed to enable adoption of thick PEDOT:PSS layers without having to worry about parasitic absorption, showing a power conversion efficiency (PCE) of 16.3%. Combined with a proper pre-condition on the Si substrate, the back-junction hybrid solar cell with 200 nm PEDOT:PSS layer received an enhanced PCE of 16.8%. In addition, the improved long-term stability for the back-junction device was also observed. The PCE remained 90% (unsealed) after being stored in ambient atmosphere for 30 days and over 80% (sealed) after 150 days.

8.
Nanotechnology ; 29(45): 45LT01, 2018 Nov 09.
Artigo em Inglês | MEDLINE | ID: mdl-30160239

RESUMO

Enhanced photoluminescence and improved internal quantum efficiency were demonstrated for ultraviolet light emitting diodes (UV-LEDs) with Al nanohole arrays deposited on the top surface. The effects of the thickness and periodicity of the plasmonic structures on the optical properties of UV-LEDs were studied, and an optimized nanohole array parameter was illustrated. Classical electrodynamic simulations showed that the radiated power is mostly concentrated along the edge of the Al nanohole arrays. Even though no obvious dip was observed in the transmission spectra associated with localized surface plasmon resonance, significant improvements in radiatiative recombination and light extraction efficiency were demonstrated, indicating the influence of Al nanohole arrays on the light emission control of UV-LEDs. It is anticipated that the enhanced luminescence can be obtained for various emitting wavelengths by directly adjusting the periodicity and morphology of the Al nanohole arrays and this new technology can alleviate crystal quality requirements of III-nitride thin films in the development of high efficiency UV optoelectronic devices.

9.
Small ; 14(15): e1704493, 2018 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-29488322

RESUMO

Surface nanotexturing with excellent light-trapping property is expected to significantly increase the conversion efficiency of solar cells. However, limited by the serious surface recombination arising from the greatly enlarged surface area, the silicon (Si) nanotexturing-based solar cells cannot yet achieve satisfactory high efficiency, which is more prominent in organic/Si hybrid solar cells (HSCs) where a uniform polymer layer can rarely be conformably coated on nanotextured substrate. Here, the HSCs featuring advanced surface texture of periodic upright nanopyramid (UNP) arrays and hole-conductive conjugated polymers, poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS), are investigated. The tetramethylammonium hydroxide etching is used to smooth the surface morphologies of the Si-UNPs, leading to reduced surface defect states. The uniform Si-UNPs together with silane chemical-incorporated PEDOT:PSS solution enable the simultaneous realization of excellent broadband light absorption as well as enhanced electrical contact between the textured Si and the conducting polymer. The resulting PEDOT:PSS/Si HSCs textured with UNP arrays show a promising power conversion efficiency of 13.8%, significantly higher than 12.1% of the cells based on the-state-of-the-art surface texture with random pyramids. These results provide a viable route toward shape-controlled nanotexturing-based high-performance organic/Si HSCs.

10.
Adv Sci (Weinh) ; 5(3): 1700547, 2018 03.
Artigo em Inglês | MEDLINE | ID: mdl-29593956

RESUMO

By combining the most successful heterojunctions (HJ) with interdigitated back contacts, crystalline silicon (c-Si) solar cells (SCs) have recently demonstrated a record efficiency of 26.6%. However, such SCs still introduce optical/electrical losses and technological issues due to parasitic absorption/Auger recombination inherent to the doped films and the complex process of integrating discrete p+- and n+-HJ contacts. These issues have motivated the search for alternative new functional materials and simplified deposition technologies, whereby carrier-selective contacts (CSCs) can be formed directly with c-Si substrates, and thereafter form IBC cells, via a dopant-free method. Screening and modifying CSC materials in a wider context is beneficial for building dopant-free HJ contacts with better performance, shedding new light on the relatively mature Si photovoltaic field. In this review, a significant number of achievements in two representative dopant-free hole-selective CSCs, i.e., poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate)/Si and transition metal oxides/Si, have been systemically presented and surveyed. The focus herein is on the latest advances in hole-selective materials modification, interfacial passivation, contact resistivity, light-trapping structure and device architecture design, etc. By analyzing the structure-property relationships of hole-selective materials and assessing their electrical transport properties, promising functional materials as well as important design concepts for such CSCs toward high-performance SCs have been highlighted.

11.
ACS Nano ; 11(12): 12687-12695, 2017 12 26.
Artigo em Inglês | MEDLINE | ID: mdl-29215861

RESUMO

Carrier recombination and light management of the dopant-free silicon/organic heterojunction solar cells (HSCs) based on poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) are the critical factors in developing high-efficiency photovoltaic devices. However, the traditional passivation technologies can hardly provide efficient surface passivation on the front surface of Si. In this study, a photoinduced electric field was induced in a bilayer antireflective coating (ARC) of polydimethylsiloxane (PDMS) and titanium oxide (TiO2) films, due to formation of an accumulation layer of negative carriers (O2- species) under UV (sunlight) illumination. This photoinduced field not only suppressed the silicon surface recombination but also enhanced the built-in potential of HSCs with 84 mV increment. In addition, this photoactive ARC also displayed the outstanding light-trapping capability. The front PEDOT:PSS/Si HSC with the saturated O2- received a champion PCE of 15.51% under AM 1.5 simulated sunlight illumination. It was clearly demonstrated that the photoinduced electric field was a simple, efficient, and low-cost method for the surface passivation and contributed to achieve a high efficiency when applied in the Si/PEDOT:PSS HSCs.

12.
Nanotechnology ; 28(47): 474001, 2017 Nov 24.
Artigo em Inglês | MEDLINE | ID: mdl-29098987

RESUMO

2D metallic arrays with binary nanostructures derived from a nanosphere lithography (NSL) method have been rarely reported. Here, we demonstrate a novel NSL strategy to fabricate highly ordered 2D gold arrays with disc-in-hole binary (DIHB) nanostructures in large scale by employing a sacrificing layer combined with a three-step lift-off process. The structural parameters of the resultant DIHB arrays, such as periodicity, hole diameter, disc diameter and thicknesses can be facilely controlled by tuning the nanospheres size, etching condition, deposition angle and duration, respectively. Due to the intimate interactions between two subcomponents, the DIHB arrays exhibit both an extraordinary high surface-enhanced Raman scattering enhancement factor up to 5 × 108 and a low sheet resistance down to 1.7 Ω/sq. Moreover, the DIHB array can also be used as a metal catalyzed chemical etching catalytic pattern to create vertically-aligned Si nano-tube arrays for anti-reflectance application. This strategy provides a universal route for synthesizing other diverse binary nanostructures with controlled morphology, and thus expands the applications of the NSL to prepare ordered nanostructures with multi-function.

13.
Sci Rep ; 7(1): 14575, 2017 11 06.
Artigo em Inglês | MEDLINE | ID: mdl-29109447

RESUMO

Recently, silicon single nanowire solar cells (SNSCs) serving as the sustainable self-power sources have been integrated into optoelectronic nanodevices under the driver of technology and economy. However, conventional SNSC cannot provide the minimum energy consumption for the operation of nanodevices due to its low power conversion efficiency (PCE). Here, we propose an innovative approach to combine the n-type silicon nanowires (SiNWs) with p-type poly(3,4-ethylthiophene):poly(styrenesulfonate) (PEDOT:PSS) to form the p + n heterojunction, which shows superior opto-electric performances. Besides, PEDOT:PSS also acts as a natural anti-reflection coating (ARC) with an excellent light-trapping capability, especially in the short-wavelength range. Importantly, the photovoltaic performances of Si/PEDOT:PSS SNSC can be well maintained even in large surface recombination velocity, due to the efficient field-effect passivation of PEDOT:PSS. The minority carrier concentration at outer surface of shallow p + n heterojunction is greatly reduced by the electric field, drastically suppressing the surface recombination compared to the conventional p-i-n homojunction SNSC. Furthermore, larger junction area of p + n heterojunction facilitates the separation of photo-generated charge carriers. These results demonstrate that the Si/PEDOT:PSS SNSC is a promising alternative for micro power application.

14.
ACS Appl Mater Interfaces ; 9(44): 38373-38380, 2017 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-29027466

RESUMO

Electron-selective layers (ESLs) and hole-selective layers (HSLs) are critical in high-efficiency organic-inorganic lead halide perovskite (PS) solar cells for charge-carrier transport, separation, and collection. We developed a procedure to assess the quality of the ESL/PS junction by measuring potential distribution on the cross section of SnO2-based PS solar cells using Kelvin probe force microscopy. Using the potential profiling, we compared three types of cells made of different ESLs but otherwise having an identical device structure: (1) cells with PS deposited directly on bare fluorine-doped SnO2 (FTO)-coated glass; (2) cells with an intrinsic SnO2 thin layer on the top of FTO as an effective ESL; and (3) cells with the SnO2 ESL and adding a self-assembled monolayer (SAM) of fullerene. The results reveal two major potential drops or electric fields at the ESL/PS and PS/HSL interfaces. The electric-field ratio between the ESL/PS and PS/HSL interfaces increased in devices as follows: FTO < SnO2-ESL < SnO2 + SAM; this sequence explains the improvements of the fill factor (FF) and open-circuit voltage (Voc). The improvement of the FF from the FTO to SnO2-ESL cells may result from the reduction in voltage loss at the PS/HSL back interface and the improvement of Voc from the prevention of hole recombination at the ESL/PS front interface. The further improvements with adding an SAM is caused by the defect passivation at the ESL/PS interface, and hence, improvement of the junction quality. These nanoelectrical findings suggest possibilities for improving the device performance by further optimizing the SnO2-based ESL material quality and the ESL/PS interface.

15.
Nanoscale ; 9(40): 15477-15483, 2017 Oct 19.
Artigo em Inglês | MEDLINE | ID: mdl-28976517

RESUMO

Poor light extraction efficiency (LEE) has been one of the major challenges responsible for the low external quantum efficiency of AlGaN-based ultraviolet light emitting Diodes (UV-LEDs). In this study, AlGaN nanostructure arrays were fabricated using a large-scale nanosphere self-assembly technique followed by reactive ion etching, and the transmission property of the AlGaN thin film and the photoluminescence (PL) behavior of AlGaN/GaN multiple-quantum-wells (MQWs) were investigated. A 90% light transmission value was obtained for the AlGaN thin film and a 2.5-fold increase in the band edge luminescence of the MQWs were obtained with an optimized nanostructure periodicity. Essentially, a general rule of periodicity-MQW emission wavelength matching criteria-was provided. Both the light transmission properties of the Al0.55Ga0.45N/AlN/sapphire thin film and the photoluminescence (PL) behavior of the AlGaN/GaN MQWs contribute to an improved understanding of the light extraction mechanism of PhC patterned UV-LEDs. Raman spectra also demonstrated the strain relaxation inside the MQW after nanostructure fabrication and thermal annealing. This study provides a pathway towards higher efficiency UV-LEDs with the help of a periodicity-wavelength matched nanostructure array.

16.
Opt Express ; 25(9): 10464-10472, 2017 May 01.
Artigo em Inglês | MEDLINE | ID: mdl-28468418

RESUMO

Surface-texture with silicon (Si) nanopyramid arrays has been considered as a promising choice for extremely high performance solar cells due to their excellent anti-reflective effects and inherent low parasitic surface areas. However, the current techniques of fabricating Si nanopyramid arrays are always complicated and cost-ineffective. Here, a high throughput nanosphere patterning method is developed to form periodic upright nanopyramid (UNP) arrays in wafer-scale. A direct comparison with the state-of-the-art texture of random pyramids is demonstrated in optical and electronic properties. In combination with the antireflection effect of a SiNx coating layer, the periodic UNP arrays help to provide a remarkable improvement in short-wavelength response over the random pyramids, attributing to a short-current density gain of 1.35 mA/cm2. The advanced texture of periodic UNP arrays provided in this work shows a huge potential to be integrated into the mass production of high-efficiency Si solar cells.

17.
Opt Lett ; 42(10): 1891-1894, 2017 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-28504752

RESUMO

A large-scale nanostructured low-temperature solar selective absorber is demonstrated experimentally. It consists of a silicon dioxide thin film coating on a rough refractory tantalum substrate, fabricated based simply on self-assembled, closely packed polystyrene nanospheres. Because of the strong light harvesting of the surface nanopatterns and constructive interference within the top silicon dioxide coating, our absorber has a much higher solar absorption (0.84) than its planar counterpart (0.78). Though its absorption is lower than that of commercial black paint with ultra-broad absorption, the greatly suppressed absorption/emission in the long range still enables a superior heat accumulation. The working temperature is as high as 196.3°C under 7-sun solar illumination in ambient conditions-much higher than those achieved by the two comparables.

18.
Sci Rep ; 7: 44576, 2017 03 14.
Artigo em Inglês | MEDLINE | ID: mdl-28291229

RESUMO

Among new flexible transparent conductive electrode (TCE) candidates, ultrathin Ag film (UTAF) is attractive for its extremely low resistance and relatively high transparency. However, the performances of UTAF based TCEs critically depend on the threshold thickness for growth of continuous Ag films and the film morphologies. Here, we demonstrate that these two parameters could be strongly altered through the modulation of substrate surface energy. By minimizing the surface energy difference between the Ag film and substrate, a 9 nm UTAF with a sheet resistance down to 6.9 Ω sq-1 can be obtained using an electron-beam evaporation process. The resultant UTAF is completely continuous and exhibits smoother morphologies and smaller optical absorbances in comparison to the counterpart of granular-type Ag film at the same thickness without surface modulation. Template-stripping procedure is further developed to transfer the UTAFs to flexible polymer matrixes and construct Al2O3/Ag/MoOx (AAM) electrodes with excellent surface morphology as well as optical and electronic characteristics, including a root-mean-square roughness below 0.21 nm, a transparency up to 93.85% at 550 nm and a sheet resistance as low as 7.39 Ω sq-1. These AAM based electrodes also show superiority in mechanical robustness, thermal oxidation stability and shape memory property.

19.
Adv Mater ; 29(15)2017 Apr.
Artigo em Inglês | MEDLINE | ID: mdl-28151568

RESUMO

Silicon/poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) heterojunction solar cells with 16.2% efficiency and excellent stability are fabricated on pyramid-textured silicon substrates by applying a water-insoluble ester as capping layer. This shows that a conformal coating of PEDOT:PSS on textured silicon can greatly improve the junction quality with the main stability failure routes related to the moisture-induced poly(3,4-ethylenedioxythiophene) aggregations and the tunneling silicon oxide autothickening.

20.
Nanoscale Res Lett ; 12(1): 26, 2017 Dec.
Artigo em Inglês | MEDLINE | ID: mdl-28070837

RESUMO

The organic/silicon (Si) hybrid heterojunction solar cells (HHSCs) have attracted considerable attention due to their potential advantages in high efficiency and low cost. However, as a newly arisen photovoltaic device, its current efficiency is still much worse than commercially available Si solar cells. Therefore, a comprehensive and systematical optoelectronic evaluation and loss analysis on this HHSC is therefore highly necessary to fully explore its efficiency potential. Here, a thoroughly optoelectronic simulation is provided on a typical planar polymer poly (3,4-ethylenedioxy thiophene):polystyrenesulfonate (PEDOT:PSS)/Si HHSC. The calculated spectra of reflection and external quantum efficiency (EQE) match well with the experimental results in a full-wavelength range. The losses in current density, which are contributed by both optical losses (i.e., reflection, electrode shield, and parasitic absorption) and electrical recombination (i.e., the bulk and surface recombination), are predicted via carefully addressing the electromagnetic and carrier-transport processes. In addition, the effects of Si doping concentrations and rear surface recombination velocities on the device performance are fully investigated. The results drawn in this study are beneficial to the guidance of designing high-performance PEDOT:PSS/Si HHSCs.

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