The detailed balance method is used to study the potential of the intermediate band solar cell (IBSC), which can improve the efficiency of the Si-based solar cell with a bandgap between 1.1 eV to 1.7 eV. It shows that a crystalline silicon solar cell with an intermediate band located at 0.36 eV below the conduction band or above the valence band can reach a limiting efficiency of 54% at the maximum light concentration, improving greatly than 40.7% of the Shockley—Queisser limit for the single junction Si solar cell. The simulation also shows that the limiting efficiency of the silicon-based solar cell increases as the bandgap increases from 1.1 eV to 1.7 eV, and the amorphous Si solar cell with a bandgap of 1.7 eV exhibits a radiative limiting efficiency of 62.47%, having a better potential. 相似文献
In an attempt to take full advantage of near-infrared part of the solar spectrum, Gd2(MoO4)3:Er3+ nanophosphors have been proposed as potential luminescent materials to enhance the response of the silicon solar-cell. Upon
excitation with low-energy near-infrared photons, intense upconverted emissions at 545, 665, 800, and 980 nm, for which energies
higher than the bandgap of silicon solar-cell, have been achieved with conversion efficiencies of 0.12%, 0.05%, 0.83%, and
1.35%, respectively. Development of nanophosphors for photovoltaic purposes could open up an approach in achieving high-efficiency
silicon-based solar-cell by means of the up-conversion of the sub-bandgap near-infrared part of the solar spectrum (E < 1.12 eV) to visible/near-infrared photons. 相似文献
Hydrogenated nanocrystalline silicon germanium thin films (nc-SiGe:H) is an interesting alternative material to replace hydrogenated
nanocrystalline silicon (nc-Si:H) as the narrow bandgap absorber in an a-Si/a-SiGe/nc-SiGe(nc-Si) triple-junction solar cell
due to its higher optical absorption in the wavelength range of interest. In this paper, we present results of optical, structural
investigations and electrical characterization of nc-SiGe:H thin films made by hot-wire chemical vapor deposition (HW-CVD)
with a coil-shaped tungsten filament and with a disilane/germane/hydrogen gas mixture. The optical band gaps of a-SiGe:H and
nc-SiGe:H thin-films, which are deposited with the same disilane/germane/hydrogen gas mixture ratio of 3.4 : 1.7 : 7, are
about 1.58 eV and 2.1 eV, respectively. The nc-SiGe:H thin film exhibits a larger optical absorption coefficient of about
2–4 in the 600–900 nm range when compared to nc-Si:H thin film. Therefore, a thinner nc-SiGe:H layer of ∼500 nm thickness
may be sufficient for the narrow bandgap absorber in an a-Si based multiple-junction solar cell. We enhanced the transport
properties as measured by the photoconductivity frequency mixing technique. These improved alloys do not necessarily show
an improvement in the degree of structural heterogeneity on the nanometer scale as measured by smallangle X-ray scattering.
Decreasing both the filament temperature and substrate temperature produced a film with relatively low structural heterogeneity
while photoluminescence showed an order of magnitude increase in defect density for a similar change in the process.
相似文献
The efficient photon harvesting in near infrared wavelength range is still a challenging problem for high performance Cu(In1-x, Gax)Se2 (CIGS) solar cell. Herein, adjusting the energy band distribution of CIGS solar cell could provide significant academic guidance for devices with superior output electric power. To understand the role of each functional layer, the optimal 3000 nm CIGS absorber layer with 1.3 eV bandgap and 30 nm CdS buffer layer were firstly obtained via simulating the uniform band-gap structures. By introducing CIGS absorber layer with a double grading Ga/(Ga+In) profile, the power conversion efficiency of the double gradient band gap cell is superior to that of uniform band-gap cell through extending absorption of near-infrared wavelength range. Upon optimization, the best power conversion efficiency of CIGS with a double gradient band gap solar cell is improved significantly to 24.90%, among the best values reported in literatures, which is an 8.17% relative increase compared with that of the uniform band-gap cell. Our findings provide a theoretical guide toward the design of high performance solar cells and enrich the understandings of the energy band engineering for developing of novel semiconductor devices. 相似文献
The optoelectronic properties of a selected group of Cu-III-VI2 chalcopyrites-based materials are deeply investigated by using the modified Becke-Johnson (mBJ) potential, combined with DFT + U approach. The obtained results are further used to calculate these materials’ theoretical efficiency limit for solar cell applications. The bandgap findings indicate a reliable ±0.2 eV agreement. After evaluating the electronic and optical properties, the spectroscopic limited maximum efficiency (SLME) model was used as a metric for the screening. Besides the bandgap value considered in the Shockley–Queisser model, the SLME requires that the absorption spectra, the radiative recombination losses, and the absorber layer thickness must be considered to adequately calculate the efficiency of considered cells. Our findings unveil that some candidates, such as CuInS2, where an SLME of 30.25% is achieved at a film width of 500 nm can be classified in the category of materials with higher power conversion efficiency. 相似文献
The Cu–CdSe–Cu nanowire heterojunctions were fabricated by sequential electrochemical deposition of layers of Cu metal and
CdSe semiconductor within the nano-pores of anodic alumina membrane templates. X-ray diffraction reveals the cubic phase for
Cu and hexagonal phase for CdSe in the electrodeposited Cu–CdSe–Cu nanowire heterojunctions. The composition of the nanowire
heterojunction segments is characterized by energy dispersive X-ray spectroscopy. The morphological study of nanowire heterojunctions
has been made using scanning electron microscope and high resolution transmission microscopy. The nanowire heterojunctions
grown in 100 and 300 nm nano-pore size templates have been found to have optical band gaps of 1.92 and 1.75 eV, respectively.
The absorption spectra of 100 nm nanowire heterojunctions show a blue shift of 0.18 eV. The collective nonlinear current–voltage
(I–V) characteristics of the 300 and 100 nm nanowire heterojunctions show their rectifying and asymmetric behaviour, respectively. 相似文献
Colloidal zinc telluride (ZnTe) nanostructures were successfully processed through a simple and facile ultrasonic (sonochemical) treatment for photoelectronic applications. The particle-like morphological features, phase and nature of valence state of various metal ions existing in ZnTe were examined using electron and X-ray photoelectron spectroscopic tools. Raman spectroscopic measurements revealed the dominance of exciton-phonon coupling and occurrence of TeO2 traces in ZnTe through the corresponding vibrations. Optical bandgap of the ZnTe suspension was estimated to be around 2.15 eV, authenticating the direct allowed transitions. The p-type electrical conductivity and charge carrier density of ZnTe were additionally estimated from the Bode, Nyquist and Mott-Schottky type impedance plots. The photoelectrical properties of ZnTe were investigated by fabricating p-ZnTe/n-Si heterostructures and studying their corresponding current-voltage characteristics under dark and white light illumination. The diodes revealed excellent rectifying behaviour with significant increase in reverse current under illumination. The stability of the devices were also affirmed through the time-dependent photoresponse characteristics, which actually suggested the improved and effective separation of photo generated electron hole pairs across the integrated heterojunctions. The obtained results also augment the potential of sonochemically processed ZnTe for application in photo detection and sensor related functions. 相似文献
The Ⅲ-V alloys and doping to tune the bandgap for solar cells and other optoelectronic devices has remained a hot topic of research for the last few decades. In the present article, the bandgap tuning and its influence on optical properties of In1-xGaxN/P, where (x = 0.0, 0.25, 0.50, 0.75, and 1.0) alloys are comprehensively analyzed by density functional theory based on full-potential linearized augmented plane wave method (FP-LAPW) and modified Becke and Johnson potentials (TB-mBJ). The direct bandgaps turn from 0.7 eV to 3.44 eV, and 1.41 eV to 2.32 eV for In1-xGaxN/P alloys, which increases their potentials for optoelectronic devices. The optical properties are discussed such as dielectric constants, refraction, absorption, optical conductivity, and reflection. The light is polarized in the low energy region with minimum reflection. The absorption and optical conduction are maxima in the visible region, and they are shifted into the ultraviolet region by Ga doping. Moreover, static dielectric constant ε1(0) is in line with the bandgap from Penn's model. 相似文献
Fabrication and electrical characterisation of microscale air bridges consisting of GaN heavily doped with silicon is described.
These were made from GaN–AlInN–GaN epitaxial trilayers on sapphire substrates, in which the AlInN was close to the composition
lattice matched to GaN at ∼17% InN fraction. The start of the fabrication sequence used inductively coupled plasma etching
with chlorine chemistry to define mesas. In situ monitoring by laser reflectometry indicated an AlInN vertical etch rate of
400 nm/minute, ∼70% of the etch rate of GaN. Processing was completed by lateral wet etching of the AlInN in hot nitric acid
to leave GaN microbridges supported between anchor posts at both ends. Deposition of Ti–Au contact pads onto the anchor posts
allowed study of the electrical characteristics. At low applied voltages, vertical conduction through the undoped AlInN layers
was minimal in comparison with the current path through the Si:GaN bridges. Typical structures showed highly linear current-voltage
characteristics at low applied voltages, and had resistances of 1050 Ω. The observed resistance values are compared with the
predicted value based on materials parameters and an idealised geometry. The microbridges showed damage from Joule heating
only at current densities above 2×105 A cm−2. 相似文献
Silicon‐based technologies provide an ideal platform for the monolithic integration of photonics and microelectronics. In this context, a variety of passive and active silicon photonic devices have been developed to operate at telecom and datacom wavelengths, at which silicon has minimal optical absorption ‐ due to its bandgap of 1.12 eV. Although in principle this transparency window limits the use of silicon for optical detection at wavelengths above 1.1 μm, in recent years tremendous advances have been made in the field of all‐silicon sub‐bandgap photodetectors at telecom and datacom wavelengths. By taking advantage of emerging materials and novel structures, these devices are becoming competitive with the more well‐established technologies, and are opening new and intriguing perspectives. In this paper, a review of the state‐of‐the‐art is presented. Devices based on defect‐mediated absorption, two‐photon absorption and the internal photoemission effect are reported, their working principles are elucidated and their performance discussed and compared.
On three different samples of crystallinep-siliconn+p-junctions have been prepared by coating the surface with a phosphorous glass and a subsequent diffusion at 915°C for 30 min. From the measurement of the short circuit current density and the open circuit voltage under high illumination conditions the diffusion current of the solar cells has been determined as a function of the temperature between 77K and 300 K. The contribution of the emitter and the base region to the diffusion current was examined. Under the assumption of Auger recombination governing the hole lifetime in the emitter the narrowing of the mobility bandgap due to the high density of states within the bandgap of the emitter was determined. A shrinkage as high as 0.18 eV was observed in the case of a 0.2 cm sample of lower purity. For high purity 6 cm silicon the reduction of the mobility bandgap was determined as 0.10 eV. A polycrystalline sample exhibits a shrinkage of 0.15 eV. The reduction of the mobility bandgap was found to determine the lower limit of the current losses due to carrier diffusion in our solar cells at current densities around 1×10–7 Am–2. 相似文献
ZnMgAlO films with a broad spectral range of optical transmission and high conductivity were prepared by pulsed laser deposition. The optical and electrical properties of ZnMgAlO films could be controlled by adjusting Al and Mg contents. As the Mg content increased from 10 to 30 at.%, the bandgap value could be modulated from 3.78 to 4.66 eV, and the transparent wavelength range was widened within near-UV, visible and near-IR regions. The optimized ZnMgAlO film possesses a wide bandgap of 4.5 eV and a low resistivity of cm. The broad spectral range of optical transmission and high conductivity maked ZnMgAlO films are of interest as TCO window materials for optoelectronic devices. 相似文献
Using first principles total energy calculations within the full-potential linearized augmented plane wave method, we have
studied the structural and electronic properties of yttrium nitride (YN) in the three phases, namely wurtzite, caesium chloride
and rocksalt structures. The calculations are performed at zero and under hydrostatic pressure. In agreement with previous
findings, it is found that the favored phase for YN is the rocksalt-like structure. We predict that at zero pressure YN in
the rocksalt structure is a semiconductor with an indirect bandgap of 0.8 eV. A phase transition from a rocksalt to a caesium
chloride structure is found to occur at ∼134 GPa. Besides, a transition from an indirect (Γ−X) bandgap semiconductor to a direct (X−X) one is predicted at pressure of ∼84 GPa. For the electron effective mass of rocksalt YN, these are the first results, to
our knowledge. The information derived from the present study may be useful for the use of YN as an active layer in electronic
devices such as diodes and transistors. 相似文献
This work proposes a new texturing technique of monocrystalline silicon surface for solar cells with sodium hypochlorite. A mixed solution consisting of 5 wt% sodium hypochlorite and 10 vl% ethanol has been found that results in a homogeneous pyramidal structure, and an optimal size of pyramids on the silicon surface. The textured silicon surface exhibits a lower average reflectivity (about 10.8%) in the main range of solar spectrum (400–1000 nm). 相似文献
Solar cells that combine single-crystalline silicon(Si) with graphene(G) have been widely researched in order to develop next-generation photovoltaic devices. However, the power conversion efficiency(PCE) of G/Si solar cell without chemical doping is commonly low due to the relatively high resistance of graphene. In this work, through combining graphene with carbon nanotube(CNT) networks, we fabricated three kinds of hybrid nanocarbon film/Si heterojunction solar cells in order to increase the PCE of the graphene based Si solar cell. We investigated the characteristics of different nanocarbon film/Si solar cells and found that their performance depends on the heterojunctions. Specifically, a doping-free G-CNT/Si solar cell demonstrated a high PCE of 7.9%, which is nearly equal to the combined value of two individuals(G/Si and CNT/Si). This high efficiency is attributed to the synergistic effect of graphene and CNTs, and can be further increased to 9.1% after applying a PMMA antireflection coating. This study provides a potential way to further improve the Si based heterojunction solar cells. 相似文献
Black silicon,produced by irradiating the surface of a silicon wafer with femtosecond laser pulses in the presence of a sulfur-bearing gas,is widely believed to be a potential material for efficient multi-intermediate-band silicon solar cells.Taking chalcogen as an example,we analyse the loss of sunlight for silicon with two impurity bands and we find that loss of the sunlight can be minimized to 0.332 when Te 0 (0.307 eV) and Te + (0.411 eV) are doped into microstructured silicon.Finally,problems needed to be resolved in analysing the relationship between conversion efficiency of the ideal four-band silicon solar cell and the position of the introduced two intermediated bands in silicon according to detailed balance theory are pointed out with great emphasis. 相似文献
We present joint experimental and theoretical results on the elastic scattering of spin-polarized electrons from an epitaxial Au film on a W(110) substrate in the energy range from 8 eV to 27 eV. A time-of-flight technique with a position-sensitive detector is applied to measure secondary emission spectra for spin-up and spin-down primary electrons in a specular geometry. The spin-asymmetry of coherently scattered electrons is obtained by selecting the diffraction spot on the detector. Regions of large asymmetries – with a maximum of about ?60 % – are identified for electron energies of about 14 eV. Relativistic multiple-scattering calculations produce spin-orbit-induced asymmetries which are in agreement with their experimental counterparts. They further reveal that large asymmetries are associated with high intensities. This offers the possibility of an efficient new spin polarimeter with a figure of merit of about 1.5 · 10?2. 相似文献