2b. While blue light has roughly twice the energy of red light, that energy is not captured by devices with a single p-n junction. Trupke, T. & Wurfel, P. Improved spectral robustness of triple tandem solar cells by combined series/parallel interconnection. On contrary, the fact that the AgNWs partially sink into N-PEDOT can reduce the roughness of the NW networks, which is beneficial for building the upper few layers and further reduces the possibility of shunts in the top subcell. Cite this article. The sunlight intensity is a parameter in the ShockleyQueisser calculation, and with more concentration, the theoretical efficiency limit increases somewhat. These two problems are solved in Ozdemir-Barone method. However, commonly used tin-based narrow-bandgap perovskites have shorter carrier diffusion lengths and lower absorption coefficient than lead- (a) Equivalent electronic circuit of the series/series (SS) triple-junction organic solar cells. Acknowledgement 23. 6:7730 doi: 10.1038/ncomms8730 (2015). In a tandem cell conguration constructed from a single material, one can achieve two dierent eective bandgaps, thereby exceeding the ShockleyQueisser limit. To install the Shockley-Queisser limit calculator: just download it: Phys. By taking this into account, the theoretical efficiency of crystalline silicon solar cells was calculated to be 29.4%.[11]. (c) STEM image of the cross-section and EDS elemental (Ag, Zn, S) maps. In the Shockley-Quiesser limit, 100% light absorption is assumed above the band gap of the material. This relies on a practical IR cell being available, but the theoretical conversion efficiency can be calculated. For organic solar cells, we followed the model proposed by Dennler et al.14,15 to calculate the efficiency potential for the four types of triple-junction architectures as a function of the bandgaps of three absorbers. One can then use the formula. The middle AgNW layer in this triple-junction device serves as a common cathode to collect electrons created by the subcells. Sci. ( Am. Detailed description of the device fabrication procedure is presented in the Methods section and schematically illustrated in Supplementary Fig. It applies to most solar cell designs in the world, except for "tandem solar cells" and some additional obscure exceptions (discussed at the end of the document). There is a trade-off in the selection of a bandgap. We used an internal quantum efficiency of 100% for our simulation41. Commun. A polymer tandem solar cell with 10.6% power conversion efficiency. [29] In contrast, considerable progress has been made in the exploration of fluorescent downshifting, which converts high-energy light (e. g., UV light) to low-energy light (e. g., red light) with a quantum efficiency smaller than 1. Mater. ADS Using methods similar to the original ShockleyQueisser analysis with these considerations in mind produces similar results; a two-layer cell can reach 42% efficiency, three-layer cells 49%, and a theoretical infinity-layer cell 68% in non-concentrated sunlight.[5]. 1c), parallel/series (PS, Supplementary Fig. The calculation of the fundamental efficiency limits of these multijunction cells works in a fashion similar to those for single-junction cells, with the caveat that some of the light will be converted to other frequencies and re-emitted within the structure. [14][15] Another proposal suggests spreading out an array of microscopic solar cells on a surface, and focusing light onto them via microlens arrays,[16] while yet another proposal suggests designing a semiconductor nanowire array in such a way that light is concentrated in the nanowires.[17]. A wide variety of optical systems can be used to concentrate sunlight, including ordinary lenses and curved mirrors, fresnel lenses, arrays of small flat mirrors, and luminescent solar concentrators. This means that during the finite time while the electron is moving forward towards the p-n junction, it may meet a slowly moving hole left behind by a previous photoexcitation. & Miyasaka, T. Organometal halide perovskites as visible-light sensitizers for photovoltaic cells. (c) Calculated JSC values of the semitransparent, opaque perovskite cells and the proposed triple-junction devices (perovskite/DPPDPP) as a function of layer thickness of the perovskite. [9]), The rate of generation of electron-hole pairs not due to incoming sunlight stays the same, so recombination minus spontaneous generation is, I In a cell at room temperature, this represents approximately 7% of all the energy falling on the cell. 2). The calculations assume that the only recombination is radiative. Rep. 4, 7154 (2014) . Semitransparent DPPDPP reference tandem cells with top AgNW electrode and the single-junction reference devices (PCDTBT:PC70BM and OPV12:PC60BM) with bottom AgNW electrode were fabricated using the same procedure as these subcells in the SP triple-junction cells. Supplementary Figures 1-7, Supplementary Notes 1-2, Supplementary Methods and Supplementary References (PDF 476 kb), This work is licensed under a Creative Commons Attribution 4.0 International License. 135, 55295532 (2013) . This allows for higher theoretical efficiencies when coupled to a low bandgap semiconductor[26] and quantum efficiencies exceeding 100% have been reported. J. Phys. Nat. This leads to a higher interest in lowering the bandgap of perovskite. where Vs is the voltage equivalent of the temperature of the sun. Herein, we chose ZnO and neutral PEDOT:PSS (N-PEDOT) as the N- and P-type charge extraction materials, respectively, because the work functions of the two materials match well with the energy levels of the donor DPP and acceptor PC60BM20,23. The majority of tandem cells that have been produced to date use three layers, tuned to blue (on top), yellow (middle) and red (bottom). 32, 236241 (2007) . Currently, the efficiency of our SP triple-junction devices is mainly limited by the mismatch of the VOC of the top subcell with the VOC of the bottom series-connected tandem subcells. 23, 43714375 (2011) . / The purpose of this study is to determine the optimum location for intermediate band in the middle of band gap of an ideal solar cell for maximum performance. Taking the photocurrent of the top subcell PCDTBT:PC70BM into consideration, the resulting contour plot of the current density distribution of the entire triple-junction solar cells as a function of the thicknesses of two DPP:PC60BM layers is depicted in Fig. In brighter light, when it is concentrated by mirrors or lenses for example, this effect is magnified. [4] According to the authors, this ratio is well approximated by ln(fQs/Qc), where f is the combination of factors fsfts/(2tc), in which f is the solid angle of the sun divided by . Due to the well-matched VOC between the perovskite cell and the series-connected tandem cell, the photocurrent delivered by the organic tandem cell, up to 2mAcm2, directly contributes to the performance enhancement of the perovskite cell. Semonin, O. E. et al. Li, N. et al. Triple junction polymer solar cells. In combination with our previous findings that the as-designed intermediate layer was able to resist high boiling-point solvent rinsing (chlorobenzene and dichlorobenzene)16, we expect that the successively established two intermediate layers are capable of coupling the series- and parallel-connected three cells into a monolithically deposited triple-junction stack. Guo, F. et al. Afterwards, ZnO and N-PEDOT were again deposited onto the second DPP:PC60BM layer using the same coating parameters as for the first deposition. It is used for semiconductors to generate electricity, as a result of solar radiation. High-performance semitransparent perovskite solar cells with solution-processed silver nanowires as top electrodes. Google Scholar. Figure 4a shows the schematic illustration of the SP triple-junction cell design, where the bottom series-connected tandem subcells in a normal structure are electrically connected in parallel with the top inverted subcell. 9, 617624 (2008) . A single material can show dierent eective bandgap, set by its absorption spectrum, which depends on its photonic structure. Get the most important science stories of the day, free in your inbox. 22, E77E80 (2010) . Eventually enough will flow across the boundary to equalize the Fermi levels of the two materials. 8, 689692 (2008) . However, radiative recombinationwhen an electron and hole recombine to create a photon that exits the cell into the airis inevitable, because it is the time-reversed process of light absorption. [12] According to Shockley-Quiesser limit, solar cell efficiency of semiconductors depend on the band gap of the material. They also can be used in concentrated photovoltaic applications (see below), where a relatively small solar cell can serve a large area. The hybrid platform offers sunlight-to-electricity conversion efficiency exceeding that imposed by the S-Q limit on the corresponding PV cells across a broad range of bandgap energies, under low optical concentration (1-300 suns), operating temperatures in the range 900-1700 K, and in simple flat panel designs. Nanoscale 7, 16421649 (2015) . This rate of generation is called Ish because it is the "short circuit" current (per unit area). In 1961, Shockley and Queisser developed a theoretical framework for determining the limiting efficiency of a single junction solar cell based on the principle of detailed balance equating the. Luque, A., Marti, A. Prog. Phys. Wide bandgap metal halide perovskites materials are of interest for application as top subcells in multijunction devices. Modern commercial mono-crystalline solar cells produce about 24% conversion efficiency, the losses due largely to practical concerns like reflection off the front of the cell and light blockage from the thin wires on the cell surface. <E g (light blue) and cool (green . 2.8 Summary and Conclusions 22. Since the act of moving an electron from the valence band to the conduction band requires energy, only photons with more than that amount of energy will produce an electron-hole pair. The multi-junction concept is the most relevant approach to overcome the ShockleyQueisser limit for single-junction photovoltaic cells. 86, 487496 (1999) . In our parallel-connected constituent subcells, the two top subcells showed series resistance of 1cm2 which is almost eight times lower than those of bottom DPPDPP subcells (Table 2). carried out the semi-empirical modelling. 2a. Adv. [20] The upconversion efficiency can be improved by controlling the optical density of states of the absorber[21] and also by tuning the angularly-selective emission characteristics. For a converter with a bandgap of 0.92 eV, efficiency is limited to 54% with a single-junction cell, and 85% for concentrated light shining on ideal components with no optical losses and only radiative recombination.[32]. Appl. They used blackbody radiation . The light intensity at each wavelength was calibrated with a standard single-crystal Si solar cell. Second ed. There are in total four types of device configurations for a triple-junction solar cell, designated as series/series (SS, Fig. Sign up for the Nature Briefing newsletter what matters in science, free to your inbox daily. Energy Mater. Phys. Nat. Under normal conditions, the atom will pull off an electron from a surrounding atom in order to neutralize itself. Based on the convenient solution-processing along with the impressive high FFs, we expect that significant enhancement in efficiency can be achieved by exploiting high-performance wide bandgap materials with matched VOC in the back subcell. Am. The ShockleyQueisser limit is calculated by examining the amount of electrical energy that is extracted per photon of incoming sunlight. Mater. The final thickness of the liftout sample was kept <100nm, to enable high quality conventional transmission electron microscopy (CTEM) imaging at an acceleration voltage of 200kV. Internet Explorer). 6, 31503170 (2013) . Prog. 2c) exhibits a VOC of 1.10V, which is identical to the reference tandem cell, suggesting the effective incorporation of AgNWs as the top electrode. The record efficiencies of few solar technologies, such as single-crystal silicon, CuInGaSe2, CdTe and GaAs solar cells are constantly shrinking the gap to their fundamental efficiency limits2. Soc. The optical simulations reveal that the as-proposed SP triple-junction organic solar cells hold the potential to achieve high efficiencies close to those of the fully series-connected counterparts, but allowing a much wider choice of material combinations. The STEM energy dispersive X-ray spectrometry (EDS) elemental maps (Ag, Zn and S) of the cross-section shown in Fig. After all the solution-processed layers were completed, Q-tips dipped with toluene were used to clean the edges of the substrate to expose the bottom ITO and middle AgNW contacts. Sista, S., Hong, Z. R., Park, M. H., Xu, Z. Christoph J. Brabec. 5b. Devos, A. A series-connected organic tandem solar cell absorbing photons in the NIR range is stacked in a four-terminal configuration behind a semitransparent perovskite cell. Google Scholar. In particular, to exceed the ShockleyQueisser limit, it is necessary for the fluorescent material to convert a single high-energy photon into several lower-energy ones (quantum efficiency > 1). overcome the ShockleyQueisser limit. Sci. The product of the short-circuit current Ish and the open-circuit voltage Voc Shockley and Queisser call the "nominal power". Electron. This is a feasible approach as there are indeed several types of far NIR semiconductors like organic donors10,11 and quantum dots12,13 with an extended absorption beyond 1,000nm. The SP and PS configurations are distinguished by the stacking sequence of the two interconnections (parallel and series) depending on which interconnection the light passes through first. A lamella containing a cross-section of the solar cell was then attached to a TEM half grid for final thinning. Since someone asked me: "I release this document and code to the public domain." Pronunciation of "Queisser": Hans-Joachim Queisser was German, so a German-speaker helped me guess how the name is pronounced. Alternatively, our results predict a significantly growing interest in ultra-low bandgap semiconductors allowing for more efficient light-harvesting for these SP triple-junction solar cells. An efficient solution-processed intermediate layer for facilitating fabrication of organic multi-junction solar cells. ACS Nano 4, 37433752 (2010) . 5c,d, if we mathematically add the JV curves of the DPPDPP subcells with the top PCDTBT or OPV12 subcell at each voltage bias (Vbias), a perfect fitting of the constructed JV curve with the experimentally measured JV curve of the triple-junction device is observed, which is consistent with Kirchhoff's law. Other recombination processes may also exist (see "Other considerations" below), but this one is absolutely required. A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells. As shown in Fig. Mater. However, the best PCEs of reported ideal-bandgap (1.3-1.4 eV) Sn-Pb PSCs with a higher 33% theoretical efficiency limit are <18%, mainly because of . To illustrate the versatile applicability of the proposed triple-junction concept, organic and organic-inorganic hybrid triple-junction solar cells are constructed by printing methods. (a) Device architecture of the SP triple-junction solar cell. The scale bar, 400nm. F.G. and C.J.B. Thermalization of photoexcited carriers with energies in excess of the bandgap limits the power conversion efficiency (PCE) 1, requiring semiconductor absorbers with longer visible-wavelength . 20, 579583 (2008) . The origin of high efficiency in low-temperature solution-processable bilayer organometal halide hybrid solar cells. However, due to finite temperature, optical excitations are possible below the optical gap. On top of the dried PEDOT:PSS, the first photoactive layer consisting of DPP and PC60BM (1:2 wt.% dissolved in a mixed solvent of chloroform and o-dichlorobenzene (9:1 vol.%)) was deposited at 45C to obtain a thickness of 50nm. . 2.7 Beyond the Shockley Queisser Limit 20. In a traditional solid-state semiconductor such as silicon, a solar cell is made from two doped crystals, one an n-type semiconductor, which has extra free electrons, and the other a p-type semiconductor, which is lacking free electrons, referred to as "holes." Subsequent calculations have used measured global solar spectra, AM 1.5, and included a back surface mirror which increases the maximum solar conversion efficiency to 33.16% for a single-junction solar cell with a bandgap of 1.34 eV. Recombination places an upper limit on the rate of production; past a certain rate there are so many holes in motion that new electrons will never make it to the p-n junction. Liftout sample for TEM was prepared with FEI Helios Nanolab 660 DualBeam FIB, from the area-of-interest containing all layers of the solar cell. (b) Contour plot of current density distribution of the entire triple-junction devices (DPPDPP/PCDTBT) as a function of the thicknesses of bottom DPP:PC60BM layers. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/, Guo, F., Li, N., Fecher, F. et al. Am. MRS Bull. Tandem polymer solar cells featuring a spectrally matched low-bandgap polymer. Q In the most common design, a high-bandgap solar cell sits on top, absorbing high-energy, shorter-wavelength light, and transmitting the rest. A current density of up to 3mAcm2 is calculated for the series-connected DPPDPP tandem cell, as a benefit of the average 53.4% transmittance (650 and 850nm) of the semitransparent perovksite cell (Supplementary Fig. Sci. V.R.R. Hirst, L. C. & Ekins-Daukes, N. J. In cases where outright performance is the only consideration, these cells have become common; they are widely used in satellite applications for instance, where the power-to-weight ratio overwhelms practically every other consideration. For a zoc of 32.4, we find zm equal to 29.0. https://doi.org/10.1038/ncomms8730. When there is a load, then V will not be zero and we have a current equal to the rate of generation of pairs due to the sunlight minus the difference between recombination and spontaneous generation: The open-circuit voltage is therefore given (assuming fc does not depend on voltage) by. The author has an hindex of 5, co-authored 8 publication(s) receiving 63 citation(s). Energy Mater. One way to reduce this waste is to use photon upconversion, i.e. We propose to deposit a transparent counter electrode and parallel-connect these semitransparent high-efficiency cells with one or more deep NIR sensitizers as back subcells. {\displaystyle f_{\omega }Q_{s}} Q {\displaystyle I_{0}[\exp(V/V_{c})-1]. 3, 15971605 (2013) . The thickness of the front perovskite layer is fixed to 200nm which corresponds to the thickness of the optimized reference cells. These cells require the use of semiconductors that can be tuned to specific frequencies, which has led to most of them being made of gallium arsenide (GaAs) compounds, often germanium for red, GaAs for yellow, and GaInP2 for blue. In the case of DPPDPP/PCDTBT triple-junction devices, for the purpose of simplicity we fixed the thickness of the top PCDTBT:PC70BM to be 80nm corresponding to the thickness of optimized single-junction reference cells. Second, the VOC of the back cell, which is consisting of a series-connection of deep NIR absorbers, can be custom fabricated by stacking an arbitrary sequence of semiconductors with different bandgaps in series. Mater. 16, 141149 (2008) . Sci. This first calculation used the 6000K black-body spectrum as an approximation to the solar spectrum. The author has contributed to research in topic(s): Solar cell & Solar cell research. To guarantee the incident light to be able to illuminate on all the three electrodes with an overlapped active area, during the JV measurement a mask with an aperture of 4.5mm2 was used to define the cell area. Nature Communications (Nat Commun) It should be noted that, even though interlayer mixing between the AgNWs and the underlying N-PEDOT layer is observed, it does not negatively affect the device performance since the N-PEDOT in the stack purely acts as a solvent protection layer. ZnO nanoparticles dispersed in isopropanol (Product N-10) and AgNW dispersion (ClearOhm Ink) were supplied by Nanograde AG and Cambrios Technologies Corporation, respectively. For a variety of reasons, holes in silicon move much more slowly than electrons. Prior to device fabrication, the laser-patterned ITO substrates were cleaned by ultra-sonication in acetone and isopropanol for 10min each. (A) Breakdown of the different loss processes leading to the band gap-dependent Shockley-Queisser limit for single junction solar cells (out, dark blue). J. In crystalline silicon, even if there are no crystalline defects, there is still Auger recombination, which occurs much more often than radiative recombination. When this occurs, the electron recombines at that atom, and the energy is lost (normally through the emission of a photon of that energy, but there are a variety of possible processes). F.G. and N.L. Guo, F. et al. [27], Also in materials where the (excited) electrons interact strongly with the remaining electrons such as Mott insulators multiple excitons can be generated. (c) Equivalent electronic circuit of the series/parallel (SP) triple-junction devices. 26, 67786784 (2014) . Kim, J. Y. et al. 136, 1213012136 (2014) . In fact this expression represents the thermodynamic upper limit of the amount of work that can be obtained from a heat source at the temperature of the sun and a heat sink at the temperature of the cell. Mater. 172054 and No. It is obvious that to maximize the use of incident photons, the thicknesses of the two DPP:PC60BM active layers should follow the red dashed line where the photocurrents generated in the two subcells are identical. Figure 6a shows the calculated JSC distribution of the three subcells of the hybrid triple-junction device as a function of the thicknesses of the back two DPP cells. In this way, sunlight creates an electric current.[6]. Having successfully constructed the individual bottom semitransparent tandem subcells and top subcell, in combination with the verified robust intermediate layers we now complete the fabrication of the entire SP triple-junction solar cells. It should be no surprise that there has been a considerable amount of research into ways to capture the energy of the carriers before they can lose it in the crystal structure. We then extend the concept to the recently emerging perovskite solar cells. I ITO-coated glass substrates (2.5 2.5)cm2 with a sheet resistance of 15sq1 were purchased from Weidner Glas and patterned with laser before use. In March 1961, an article entitled Detailed Balance Limit of Efficiency of p-n Junction Solar Cells by William Shockley and Hans Joachim Queisser appeared in the Journal of Applied Physics (Shockley & Queisser, 1961).Following an earlier rejection by the journal (Marx, 2014; Queisser, 2007) and barely noticed for several years after publication, this article has now become an . Compared with the reference DPPDPP tandem cell, the slightly reduced VOC of 0.020.03V can be attributed to shadow effect36, because a mask with an aperture smaller than either electrode was adopted to define the active area during the JV measurement. Nat Commun 6, 7730 (2015). c Design rules for donors in bulk-heterojunction solar cells - Towards 10% energy-conversion efficiency. The ratio of the open-circuit voltage to the band-gap voltage Shockley and Queisser call V. Under open-circuit conditions, we have. 96, 23472351 (2004) . AM1.5 Spectrum An efficient triple-junction polymer solar cell having a power conversion efficiency exceeding 11%. (At that value, 22% of the blackbody radiation energy would be below the band gap.) (c) Typical JV curves of the single-junction DPP reference cell, tandem DPPDPP reference cell and the semitransparent tandem DPPDPP cell with AgNW top electrode. 3). That atom will then attempt to remove an electron from another atom, and so forth, producing an ionization chain reaction that moves through the cell. conceived the device concept. The Shockley-Queisser limit for the efficiency of a solar cell, without concentration of solar radiation. t exp Hendriks, K. H., Li, W. W., Wienk, M. M. & Janssen, R. A. J. Small-bandgap semiconducting polymers with high near-infrared photoresponse. The cell may be more sensitive to these lower-energy photons. Org. Light absorbers DPP, OPV12 and PCDTBT were purchased from BASF, Polyera and 1-Materials, respectively. These cells use multiple p-n junctions, each one tuned to a particular frequency of the spectrum. Efficient organic solar cells with solution-processed silver nanowire electrodes. where Moreover, it should be noted that although our triple-junction cells have achieved PCEs of 5.35 and 5.43%, which are higher than either one of the single-junction reference devices, those values are still 0.4% lower than the sum PCEs of the incorporated subcells. 4. However, the parallel-connection is more difficult to adapt and optimize for the high-performance semiconductors with non-tunable bandgaps, such as single-crystal silicon or CdTe. Shockley and Queisser call the ratio of power extracted to IshVoc the impedance matching factor, m. (It is also called the fill factor.) Adv. and C.J.B. Like electrons, holes move around the material, and will be attracted towards a source of electrons. Thermal upconversion is based on the absorption of photons with low energies in the upconverter, which heats up and re-emits photons with higher energies. Letting ts be 1, and using the values mentioned above of 44%, 77%, and 86.5% for the three factors gives about 29% overall efficiency. Using the above-mentioned values of Qs and Qc, this gives a ratio of open-circuit voltage to thermal voltage of 32.4 (Voc equal to 77% of the band gap). The Shockley-Queisser-limit is a theoretical limit for solar cells. These results demonstrated the excellent functionality of the ZnO/N-PEDOT intermediate layer in the series-connected tandem architecture. A more recent reference gives, for a single-junction cell, a theoretical peak performance of about 33.7%, or about 337 W/m2 in AM1.5.[1][10]. Simultaneously, optical simulations based on the transfer matrix formalism were carried out to calculate the current generation in the individual subcells34,35, which can provide valuable guidance for optimization of our SP triple-junction devices. Nevertheless, these results in combination with the high FFs of up to 68% eventually suggest that the engineered intermediate layers have efficiently coupled the three cells into triple-junction with an integrated SP interconnection. The theory is described by W. Shockley and H. J. Queisser in Journal of Applied Physics 32 (1961). The semitransparent perovskite device shows a JSC=16.28mAcm2, VOC=0.94V and FF=65.6%, yielding a PCE of 10.04%. Thus, the novel triple-junction concept demonstrated in this work provides an easy but elegant way to manufacture highly efficient photovoltaic cells, not only for conventional but also for the emerging solar technologies. Efficient tandem and triple-junction polymer solar cells.
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