If you want to rank on the first page or in the first spot, you need to focus on all three, and not just one or two out of three. The first component of Google's trust has to do with age. But it's not just the age when you first registered your website. The indexed age has to do with two factors: i the date that Google originally found your website, and; ii what happened between the time that Google found your website and the present moment in time.
Just think about any relationship for a moment. How long you've known a person is incredibly important. It's not the be-all-end-all, but it is fundamental to trust. If you've known someone for years and years and other people that you know who you already trust can vouch for that person, then you're far more likely to trust them, right?
But if you've just met someone, and haven't really vetted them so to speak, how can you possibly trust them? What's the authority of your website or webpage, or any other page on the internet for that matter where you're attempting to gain visibility? Authority is an important component of trust, and it relies heavily on quality links coming from websites that Google already trusts. Authority largely relates to the off-page optimization discipline of SEO that occurs away from the webpage as opposed to the on-page optimization that occurs directly on the webpage. For example, what are the quality and quantity of the links that have been created over time?
Are they natural and organic links stemming from relevant and high quality content, or are they spammy links, unnatural links or coming from bad link neighborhoods? Are all the links coming from the same few websites over time or is there a healthy amount of global IP diversification in the links? Content is king. It always has been and it always will be. Creating insightful, engaging and unique content should be at the heart of any online marketing strategy.
Too often, people simply don't obey this rule. The problem? This takes an extraordinary amount of work. However, anyone that tells you that content isn't important, is not being fully transparent with you. You cannot excel in marketing anything on the internet without having quality content. Quality content is more likely to get shared. Remember, this happens as a component of time.
Google knows you can't just go out there and create massive amounts of content in a few days. If you try to spin content or duplicate it in any fashion, you'll suffer a Google penalty and your visibility will be stifled. Okay, if you're still with me, fantastic. You're one of the few that doesn't mind wading through a little bit of hopeless murkiness to reemerge on the shores of hope. But before we jump too far ahead, it's important to understand what online marketing is and what it isn't. That definition provides a core understanding of what it takes to peddle anything on the web, whether it's a product, service or information.
When we talk about marketing on the internet, we're talking about driving traffic or boosting visibility via a number of means. Some of these can be broken down into organic marketing and others can be categorized as paid marketing. Organic, of course, is the allure of marketing professionals from around the planet. It's free and its unencumbered traffic that simply keeps coming.
Paid marketing, on the other hand, is still a very attractive proposition as long as the marketing pays for itself by having the right type of offer that converts. SEO should be a core tactic in any marketing strategy. While it might seem difficult to understand at first, as long as you find the right course , book or audiobook , and devote your time to learning, you'll be in good shape.
Organic SEO's flip-side offers up a paid method for marketing on search engines like Google. SEM provides an avenue for displaying ads through networks such as Google's Adwords and other paid search platforms that exist across the web throughout social media sites like Facebook, Instagram and even video sites like YouTube, which, invariably, is the world's second largest search engine.
By utilizing SEM, it provides you with a great avenue for getting the word out quickly and effectively. If you have the budget, then marketing on search engines for competitive keywords might be the right fit for you. But be prepared to pony up. The lower the competition, the lower the quality score and the lower the price. However, SEM doesn't just cover paying for clicks, but also paying for impressions.
That means, for example, that every times your ad is displayed, you pay a pre-arranged amount, regardless of whether anyone clicked on it or not. While this is a less popular form of advertising, it still exists today on some platforms. One of the hottest forms of marketing anything online right now is through social media channels such as Facebook and Instagram, amongst others. Social media provides a near-direct avenue for reaching the masses, but it most certainly isn't a simple or easy thing to achieve saturation, especially when we're talking about millions of followers.
However, getting that saturation is a frustrating process. Upconversion in solar cells was calculated to potentially lead to a maximum conversion efficiency of This optimum is reached for a solar cell material of approximately 2-eV bandgap. The analysis of the energy content of the incident AM1.
An extension to the models described above was presented in a study by Trupke et al. Using an AM1. For silicon, the limiting efficiency would be Badescu and Badescu [ 48 ] have presented an improved model that takes into account the refractive index of solar cell and converter materials in a proper manner. Two configurations are studied: cell and rear converter, the usual upconverter application, and front converter and cell FC-C. They confirm the earlier results of Trupke et al.
Also, the FC-C combination, i. Further, building on the work by Trupke et al. In practice, a converter layer may have a lower refractive index 1. Finally, a recent study on realistic upconverter and solar cell systems, in which non-ideal cell and upconverters were considered, corroborates the above findings [ 50 ]. In this study, non-ideal absorption and radiative recombination, as well as non-radiative relaxation in the upconverter, were taken into account.
Atre and Dionne also stressed that thin-film PV with wide-bandgap materials may benefit the most from including upconverters [ 50 ]. An efficiency of the solar cell of 2. Secondly, the design was such that not all emitted photons were directed to the solar cell. Richards and Shalav [ 51 ] showed upconversion under a lower excitation density of 2. This was for a system optimized for the wavelength of 1, nm. Intensity-dependent measurements showed that the upconversion efficiency was approaching its maximum due to saturation effects [ 51 , 52 ]. Under broadband excitation, upconversion was shown for the same system by Goldschmidt et al.
Since c-Si has a rather small bandgap 1. Hence, the efficiency gain for larger bandgap solar cells is expected to be higher. Upconversion of nm light was also demonstrated in DSSCs [ 54 , 55 ] and of nm light in ultrathin 50 nm a-Si:H solar cells in [ 56 ]. In the latter proof-of-principle experiment, for the first time, an organic upconverter was applied.
Typically, the active Si layer in the cells has a thickness of nm, and the generated current is The purpose of an upconverter is to tune the energy of the emitted photons to the energy where the spectral response shows a maximum. If the energy of the emitted photons is too close to the absorption limit the bandgap edge , then the absorption is too low and the upconverted light would not be fully used. These two effects can be achieved with the upconversion layer, combined with a highly reflecting back contact.
Besides a-Si, a material denoted as protocrystalline Si could be used; this is an amorphous material that is characterized by an enhanced medium-range structural order and a higher stability against light-induced degradation compared to standard amorphous silicon. An external quantum efficiency of 0. The resulting light emission in the green and red regions is very well absorbed by the cell with very good quantum efficiency for electron—hole generation.
The upconverter powder mixture was applied to the rear of the solar cells by first dissolving it in a solution of PMMA in chloroform, after which it was drop cast. With illumination from the back, the efficiency is lower because the generation profile is reversed within the cell, and thus, the photogenerated minority carriers have to travel the largest mean distance, rather than the majority carriers. The spectral response measured through the n-layer shows a quantum efficiency of 0. The thickness of the i-layer was chosen such that an interference maximum occurs at nm, increasing the transmission at this wavelength.
As a result, more light can be absorbed by the upconverter layer in the case of the flat solar cell configuration. Concentration levels of up to 25 times were reached using near-infrared light from a solar simulator. The absorption is highest around nm. The upconverter was already shown to be very efficient at low light intensities. Although the absorption at nm 1. This may be attributed to the perfectly resonant energy transfer step of nm 1.
Upconverted emission and absorption spectra of the upconverter in PMMA layer. For further experiments, the upconverter was excited at nm with a pulsed Opotek Opolette laser. Because upconversion is a two-photon process, the efficiency should be quadratically dependent on the excitation power density. The intensity of the laser light was varied with neutral density filters. Upconversion spectra were recorded in the range of to nm under identical conditions with varying excitation power.
By comparing the emission intensities, it becomes clear that the emission intensity is not increasing quadratically with excitation power density. Instead, emissions from higher and lower energy states are visible. Upconverted emission spectra under low and high excitation density. For the low excitation power, the green state was not yet saturated. The intensities may be compared. The sub-bandgap response in the near infrared due to the band tails of a-Si:H solar cells cannot be neglected [ 58 ]. To distinguish between upconverter response and sub-bandgap response, intensity-dependent current—voltage measurements are performed on solar cells with and without an upconverter at wavelengths longer than nm using a solar simulator and a nm-long pass filter.
Intrinsic response of the band tails is linearly dependent on the light intensity, while response due to upconverted light is expected to be quadratically increasing with the concentration. As expected, the sub-bandgap response linearly increases with light intensity and values of n larger than 1 are measured for the upconversion solar cells. Clearly, the current is not increasing quadratically with increasing concentration.
It is unlikely that the upconverter is saturated because the power density is far below the saturation level of 0. It is therefore more likely that the deviations are due to decreasing carrier collection efficiency with increasing concentration. This effect would play a larger role in textured solar cells because they have a higher defect density than flat solar cells. This may explain why the value of n is closer to 2 for flat solar cells than for textured solar cells. Current measured in the solar cells under illumination of sub-bandgap light.
In the upper graph, the total current of the reference and UC cells are plotted as a function of the concentration factor, while in the lower graph, the current generated by the upconverter is shown. The slope for sub-bandgap response is 1 for flat and textured solar cells. The contribution of the upconverter increases the slope slightly; when corrected for the sub-bandgap response, the slope is 1.
Monochromatic laser light with wavelength at nm and a power density of 0. Evidently, the contribution of sub-bandgap absorption is much smaller using monochromatic laser light.
The current due to the upconverter is comparable to the current measured under 20 sun: approximately 0. This is remarkable in two ways. First, the results are in contrast with previously reported experiments with broadband excitation of c-Si solar cells [ 53 ], where the current under broadband excitation was much smaller than that under laser light excitation. However, in [ 53 ], another upconverter was applied NaYF 4 and different processes occur in the upconverter, namely excited state absorption.
This is three times less than the power density of the laser. A large difference here is that for broadband illumination, a nm-long pass filter was used. Addition of other paths that lead to upconverted light may contribute to the current. Wavelengths required for these transitions are around 1, and 1, nm, which are present within the broad excitation spectrum. Contribution of these upconversion routes increases the emission and thereby the current in the solar cells.
Upconversion for solar cells is an emerging field, and the contribution of upconverter research to upconverter solar cell research increases rapidly. However, up to now, only proof-of-principle experiments have been performed on solar cells, mainly due to the high intensities that are deemed necessary. Some routes to enhance absorption are presently being developed, such as external sensitization and plasmonics. External sensitization can be achieved by, e. Quantum dots QDs can be incorporated in a concentrator plate where the QDs absorb over a broad spectral range in the IR and emit in a narrow line, e.
The viability of this concept was proven by Pan et al. With the QDs, more light was absorbed and upconverted, which was proven by measuring the excitation spectra for the upconverted emission. The increased upconverted emission resulted in higher currents in the solar cell. More challenging are options to enhance upconversion efficiencies by manipulating emission and excitation processes through plasmonic coupling [ 61 ].
The use of plasmonic effects with upconverter materials is a new and emerging field, with many possibilities and challenges. In general, plasmonic resonance can be used in two ways to increase the upconversion efficiency: by enhancing either the absorption strength or the emission strength. When the absorption strength is enhanced, the emission increases with the square of the enhancement in the non-linear regime.techkderhadubus.tk/another-christmas.php
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In the case of resonance between the plasmon and the optical transition, strong enhancement can be achieved. Recently, Atre et al. A fold increase in absorption as well as a fold increase in above-bandgap power emission toward the solar cell was calculated. A similar study has been performed using Au nanoparticles [ 63 ]. Experimental proof has recently been reported by Saboktakin et al. A related method is to enhance the absorption strength by nanofocusing of light in tapered metallic structures [ 65 ].
At the edges, enhancement has been reported due to focusing of the light in these areas. The other option is enhancing the emission. In this case, the emission of the upconverter is enhanced by nearby plasmon resonances [ 66 ]. Since the field enhancement decays away exponentially with the distance to metallic nanoparticle, the upconverter species have to be close to the surface of the nanoparticle to benefit from the field enhancement effects. For organic molecules, this presents no problem because the molecules are small enough to be placed in the field.
Besides a-Si, a material denoted as protocrystalline Si could be used; this is an amorphous material that is characterized by an enhanced medium range structural order and a higher stability against light-induced degradation compared to standard amorphous silicon. De Wild et al. An external quantum efficiency of 0. The resulting light emission in the green and red region is very well absorbed by the cell with very good quantum efficiency for electron-hole generation.
Upconversion systems consisting of lanthanide nanocrystals of YbPO 4 and LuPO 4 have been demonstrated to be visible by the naked eye in transparent solutions, however at efficiency lower than solid state up conversion phosphors Suyver et al. Further efficiency increase is possible by growing a shell of undoped NaYF 4 around the nanocrystal; in addition, surface modification is needed to allow dissolution in water, for use in biological labeling.
Porous silicon layers are investigated for use as up converter layers as host for rare-earth ions, because these ions can easily penetrate the host due to the large surface area and porosity. Sensitized triplet-triplet annihilation TTA using highly photostable metal-organic chromophores in conjunction with energetically appropriate aromatic hydrocarbons has been shown to be another alternative up conversion system Singh-Rachford et al.
This mechanism was shown to take place under ambient laboratory conditions, i. These chromophores porphyins in this case can be easily incorporated in a solid polymer so that the materials can be treated as thin film materials Islangulov et al. A problem with TTA upconverters is the spectral range. No efficient upconversion of NIR radiation at wavelengths beyond nm has been reported which limits the use to very wide bandgap solar cells Singh-Rachford et al, An extension to the models described above was presented in a study by Trupke et al.
Using an AM1. For silicon, the limiting efficiency would be Badescu and Badescu have presented an improved model, that according to them it appropriately takes into account the refractive index of solar cell and converter materials. Two configurations are studied: cell and rear converter C-RC , the usual up converter application, and front converter and cell FC-C , respectively.
They confirm the earlier results of Trupke et al. Also, the FC-C combination, i. Further, by studying the variation of refractive indexes of cell and converter separately, as opposed to Trupke et al. In practice, a converter layer may have a lower refractive index 1. Analogous to the model for up converters they studied FC-C and C-RC configurations, with down conversion or shifting properties. First, neglecting non-radiative recombination, Badescu et al.
Second, including radiative recombination for both converter and cell does only increase the efficiency for high near unity radiative recombination efficiency values. Interestingly, they report that in this case the C-RC combination cell-rear converter yields a higher efficiency than the FC-C combination in high-quality solar cells, while for low quality solar cells, this is reversed. More realistic device values and allowing for different refractive indices in cell and converter was studied by Badescu and De Vos , leading to the conclusion that in reality down converters may not always be beneficial.
However, extending the model once more, with the inclusion of anti-reflection coating and light trapping texture, showed a limiting efficiency of The model was used to select candidate materials for up- and down-conversion, but was set-up for use with rare-earth ions. Modelling downshifting layers on solar cells was also extended for non-AM1. Here, the PC1D model Basore and Clugston was used to model quantum dots dispersed in a PMMA layer on top of a multi-crystalline silicon cell mc-Si as function of the concentration of quantum dots.
The annual short circuit increase was determined at For mc-Si cells with improved surface passivation and a concomitant improved blue response the relative short current increase has been calculated to be lower Van Sark Modeling large area LSCs has indicated the importance of top-surface losses that occur through the escape cone Chatten et al. The photon concentration ratio, C, which is the ratio of the concentrated flux escaping the right-hand surface of the LSC to the flux incident on the top surface, is 4.
However, since the concentrated flux escaping the right-hand surface is a narrow-band matched to the spectral response of the cell it can all be converted and the idealized LSC would produce 8 times the current compared to the cell alone exposed to AM1. This lead to the use of wavelength-selective cholesteric liquid crystal coatings applied to the top surface in order to reduce the losses Debije et al.
Ray-tracing for LSCs uses basic ray-tracing principles, which means that a ray representing light of a certain wavelength travelling in a certain direction, is traced until it leaves the system e. The main extension to the standard ray-tracing model is the handling of the absorption and emission by the luminescent species in the LSC. With the ray-tracing model the efficiency of this plate together with a mc-Si solar cell was determined to be 2.
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Results for attaining efficiencies for other configurations are shown in Table 1 Van Sark et al. Thus, the use of GaAs or InGaP cells will result in higher efficiencies, but these cells are more expensive. A cost calculation must be performed to determine if the combination of the luminescent concentrator with this type of cells is an interesting alternative to mc-Si based solar technology.
A Lambertian mirror is one that reflects radiation isotropically. Currie et al.
Annual performance has been modeled using an LSC of which the properties and geometry resulted from a cost-per-unit-of-power optimization study by Bende et al. A square plate of The annual yield of this LSC was determined using realistic spectra representative for the Netherlands from Houshyani Hassanzadeh and collaborators and amounted to Two issues remain to be solved before downconverters can be applied in solar cells: the absorption strength needs to be increased as the transitions involved for the trivalent lanthanides are sharp and weak parity forbidden.
A second issue is concentration quenching. High Yb-concentrations are needed for efficient energy transfer as every donor Tb, Pr or Tm needs to have two Yb-neighbours for energy transfer. For these high concentrations, energy migration over the Yb-sublattice occurs and trapping of the migrating excitation energy by quenching sites strongly reduces the emission output. At present research is conducted to resolve these issues.
In principle, such sensitization can be realized in an efficient and cost-effective manner by the inclusion of a sensitizer ion. Concentration quenching may be limited by optimization of the synthesis conditions less quenching sites while also the synthesis of nanocrystals may be beneficial. In nanocrystals the volume probed by energy migration is limited due to the small size of the nanocrystal and for defect-free nanocrystals high quantum yields can be expected, similar to the increase in quantum yield observed for quantum dots vs.
For upconverters based on lanthanides absorption strengths need also to be increased and quenching decreased. In addition, upconversion could be useful for solar cells with band gap higher than that of crystalline silicon; thus, research is directed toward optimum matching of NIR absorption and visible emission with the band gap of the solar cell to which the up converter is attached. This is still an experimental challenge. The usefulness of down- and upconversion and downshifting depends on the incident spectrum and intensity.
While solar cells are designed and tested according to the ASTM standard ASTM , these conditions are rarely met outdoors, as discussed by Makrides and collaborators in Chapter 8 of this book.
Spectral conditions for solar cells vary from AM0 extraterrestrial via AM1 equator, summer and winter solstice to AM10 sunrise, sunset. The weighted average photon energy APE Minemoto et al. Further, overcast skies cause higher scattering leading to diffuse spectra, which are blue-rich, e. Thus, luminescent solar concentrators are expected to be deployed successfully in such regions Van Sark et al. In contrast, solar cells with UC layers will be performing well in countries with high direct irradiation fractions or in early morning and evening due to the high air mass resulting in low APE, albeit that the non-linear response to intensity may be limiting.
The variation of the incident spectra are of particular concern for series-connected multiple junction cells, such as triple a-Si:H Krishnan et al.
Broadband energy transfer to sensitizing dyes by mobile quantum dot mediators in solar cells
Current-mismatch due to spectral differences with respect to the AM1. It has been shown that the calculated limiting efficiency of a GaAs-based triple cell is reduced to A single cell with an UC layer, having an AM1. Successfully optimizing absorption strength and quenching in lanthanides based down converters will bring the theoretical limits within reach. Future use of DS layers on top of solar cells may be limited as blue response of present cells will advance to higher levels Van Sark On the other hand, these improvements might require additional expensive processing, while application of a DS layer is expected to be low-cost, as it only involves coating of a plastic with dispersed luminescent species.
Much progress has occurred, which is illustrated by the recent efficiency record of 7. Here, quantum dots or nanorods may have to be used, as their broad absorption spectrum is very favourable. Stability could be improved using multishell QDs Koole et al. An different approach was presented recently that employs resonance-shifting to circumvent reabsorption losses Giebink et al.
Alternatively, the originally proposed three-plate stack Goetzberger and Greubel could be further developed using perhaps a combination of organic dyes and nanocrystals, or even rare earth ions Rowan et al. The possibility to tune chemical and physical properties in nanosized materials could have a transformational effect on the performance of solar cells and one of the prominent research areas of nanomaterials for photovoltaics involves spectral conversion. In this chapter we reviewed pathways of spectrum modification for application in solar cells by means of down- and upconversion, and downshifting.
Nanoparticles, based on semiconductors or lanthanides, embedded in predominantly polymer layers on top or at the back of solar cells are an essential ingredient of spectral conversion mechanisms that may potentially lead to higher solar cell conversion efficiencies. Nanomaterial synthesis and nanotechnology will play a key role in this. The authors gratefully acknowledge numerous colleagues at Utrecht University and elsewhere who contributed to the presented work. Help us write another book on this subject and reach those readers.
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