https://doi.org/10.1038/ncomms8730. For thick enough materials this can cause significant absorption. Chalcogenophene comonomer comparison in small band gap diketopyrrolopyrrole-based conjugated polymers for high-performing field-effect transistors and organic solar cells. Luque, Antonio, and Antonio Mart. It should be noted that the absorption of the DPP polymer donor shows a red-shift of only 50nm compared with the perovskite and, therefore, we expect a significant enhancement when deeper NIR sensitizers are used as back series-connected tandem cells. 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. Commun. 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 is worth mentioning that our second intermediate layer with incorporated AgNWs exhibits an average transmittance of 84.5% (400800nm), which is a distinct advantage over evaporated thin metal films with low transmittance of 3050% as middle electrode in realizing parallel-connection.31,32 Noticeably, the semitransparent tandem DPPDPP cell shows an average transmittance of 35.6% in the range of 450650nm, which ensures for most wide bandgap materials to be applicable as top subcell to effectively harvest the transmitted photons. F.G. and K.F. Photovoltaics 19, 286293 (2011) . J. Appl. c Google Scholar. 1a) and parallel/parallel (PP, Supplementary Fig. The dominant losses responsible for the Shockley-Queisser limit are below band-gap and thermalization (hot carrier) losses; together, they account for >55% of the total absorbed solar energy. Chem. Devos, A. The calculations assume that the only recombination is radiative. Hadipour, A., de Boer, B. An efficient solution-processed intermediate layer for facilitating fabrication of organic multi-junction solar cells. Sign up for the Nature Briefing newsletter what matters in science, free to your inbox daily. ADS The most widely explored path to higher efficiency solar cells has been multijunction photovoltaic cells, also known as "tandem cells". overcome the ShockleyQueisser limit. . Therefore, many high-performance semiconductors with high external quantum efficiency (EQE) in the NIR absorption range exhibit limited applicability for multi-junction operation, as the perfectly matching semiconductor for the front or back subcells is missing. Figure 6b shows the measured JV curves of the experimentally constructed hybrid triple-junction solar cell and the corresponding subcells. Sci. The Shockley-Queisser limit can be exceeded by tandem solar cells, concentrating sunlight onto the cell, and other methods. Mater. Rep. 4, 7154 (2014) . Dennler, G. et al. 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 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. This is a very small effect, but Shockley and Queisser assume that the total rate of recombination (see below) when the voltage across the cell is zero (short circuit or no light) is proportional to the blackbody radiation Qc. exp of states. Our recent work demonstrated that a thin layer of ZnO nanoparticles can effectively conduct electrons to the AgNW electrode and, more importantly, enable the deposition of the AgNW electrode by doctor blading from water-based solution.16,17 However, both ZnO and AgNW layers are obviously not compact enough to protect the underlying subcells from solvent infiltration during the top subcell deposition. They used blackbody radiation . To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/, Guo, F., Li, N., Fecher, F. et al. This is due to the fact that the charge injections in the top subcells are higher than in the bottom subcells at Vbias>VOC. The sunlight intensity is a parameter in the ShockleyQueisser calculation, and with more concentration, the theoretical efficiency limit increases somewhat. Fei Guo and Ning Li: These authors contributed equally to this work. Due to the lack of the back reflective electrode, the semitransparent tandem device shows a relatively low short circuit current (JSC) of 5.16mAcm2. The outcome of the simulations is shown in Fig. The middle AgNW layer in this triple-junction device serves as a common cathode to collect electrons created by the subcells. Design rules for donors in bulk-heterojunction tandem solar cells-towards 15% energy-conversion efficiency. Using an AM 1.5 solar spectrum, a solar cell with an ideal band gap light absorber (band gap, Eg = 1.4 eV) could have an upper limit on PCE of 33.7%, 6 i.e., a maximum electrical power generation of 337 W m2. However, the reverse process must also be possible, according to the principle of detailed balance: an electron and a hole can meet and recombine, emitting a photon. Article As the ratio Vc/Vs goes to zero, the open-circuit voltage goes to the band-gap voltage, and as it goes to one, the open-circuit voltage goes to zero. Based on rational interface engineering, two fully solution-processed intermediate layers are successively developed, allowing effectively coupling the three cells into a SP interconnected triple-junction configuration. 96, 23472351 (2004) . Sci. 44, 75327539 (2005) . In this manuscript, we present an interconnection approach as a technologically attractive solution to address all these challenges. the bandgap energy Eg=1.4 eV. Thus the spectrum losses represent the vast majority of lost power. Efficient tandem and triple-junction polymer solar cells. 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 . 3). Mater. 22, E77E80 (2010) . ADS 9, 617624 (2008) . Zhao, N. et al. In physics, the radiative efficiency limit (also known as the detailed balance limit, ShockleyQueisser limit, Shockley Queisser Efficiency Limit or SQ Limit) is the maximum theoretical efficiency of a solar cell using a single p-n junction to collect power from the cell where the only loss mechanism is radiative recombination in the solar cell. The factor of 2 was included on the assumption that radiation emitted by the cell goes in both directions. Organometal halide perovskites have emerged as promising materials that enable fabrication of highly efficient solar cells by solution deposition38,39,40. Solar energy falling on the plate, typically black-painted metal, is re-emitted as lower-energy IR, which can then be captured in an IR cell. Module datasheets normally list this temperature dependency as TNOCT (NOCT - Nominal Operating Cell Temperature). It is not actually possible to get this amount of power out of the cell, but we can get close (see "Impedance matching" below). & Nozik, A. J. MRS Bull. To verify the compatibility of the two wide bandgap donors with the AgNW electrode, single-junction reference cells of PCDTBT:PC70BM and OPV12:PC60BM were first processed on both indium tin oxide (ITO) and AgNWs-coated glass substrates for comparison (Fig. 4, 1446 (2013) . The scale bar, 200nm. (a) Calculated JSC distribution of the three subcells as a function of the back two DPP:PC60BM film thicknesses. 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. The V loss t otal of OSCs can be expressed in terms of E 1, E 2, and E 3 in V loss total = (E g PV /q V oc SQ) + (V oc SQ V oc Rad) + (V oc Rad V oc PV) = E 1 + E 2 + E 3, where q, E g PV, V oc SQ, V oc rad, and V oc PV are the elementary charge, photovoltaic band gap, maximum voltage in the Shockley-Queisser (SQ) limit . 300 K . One way to reduce this waste is to use photon upconversion, i.e. 2b. & Peumans, P. Solution-processed metal nanowire mesh transparent electrodes. 1 16, 141149 (2008) . Electrons can be excited by light as well as by heat. Am. Am. 2.8 Summary and Conclusions 22. In the extreme limit, for a multi-junction solar cell with an infinite number of layers, the corresponding limit is 68.7% for normal sunlight,[4] or 86.8% using concentrated sunlight[5] (see solar cell efficiency). Recombination between electrons and holes is detrimental in a solar cell, so designers try to minimize it. The liftout sample was prepared using a focused ion beam (FIB, FEI Helios NanoLab 660) and imaged subsequently with the TITAN3 aberration-corrected TEM. Nat. These photons will pass through the solar cell without being absorbed by the device. Among them, the multi-junction concept is one of the most promising candidates that allows to simultaneously address the two dominant loss mechanisms4, namely, sub-bandgap transmission and thermalization losses, which account for >55% of the total energy of the solar radiation9. C.J.B., F.G. and N.L. However, one distinct drawback of the series-connected configuration is the stringent current-matching criterion, which requires careful bandgap engineering in combination with an excellent control of the thicknesses of the respective subcells. Nat Commun 6, 7730 (2015). State-of-the-art halide perovskite solar cells have bandgaps larger than 1.45 eV, which restricts their potential for realizing the Shockley-Queisser limit. Microcavity-enhanced light-trapping for highly efficient organic parallel tandem solar cells. <E g (light blue) and cool (green . acknowledge financial support from the Ministry of Education, Science and Technological Development of the Republic of Serbia (Grants No. and V.V.R. Org. D. Appl. Given that the perovskite single cell (mixed halide CH3NH3PbI3xClx) provides a high VOC of 1V, which is comparable to our series-connected DPPDPP cells, it is straightforward to fabricate a PS connected triple-junction device by placing a DPPDPP cell behind a semitransparent perovskite cell, and thereby adding up the total current density for the hybrid triple-junction device. Limiting solar cell efficiency as a function of the material bandgap for one-sun illumination. 136, 1213012136 (2014) . Hereafter, we shall experimentally show that the SP triple-junction configuration can be fabricated with the intermediate electrode and all the semiconducting layers solution-processed. The incident solar spectrum is approximated as a 6000 K blackbody spectrum. 6, Erlangen, 91052, Germany, Carina Bronnbauer,Yi Hou&Christoph J. Brabec, Center for Nanoanalysis and Electron Microscopy (CENEM), Friedrich-Alexander University Erlangen-Nrnberg, Cauerstrasse 6, Erlangen, 91058, Germany, Vuk V. Radmilovi,Velimir R. Radmilovi&Erdmann Spiecker, Innovation Center, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade, 11120, Serbia, Nanotechnology and Functional Materials Center, Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, Belgrade, 11120, Serbia, You can also search for this author in Phys. One can see that maximum photocurrents of 10mAcm2 are achievable for our DPPDPP/PCDTBT triple-junction devices when the thicknesses of the bottom and top DPP:PC60BM subcells are in the range of 3060nm and 3580nm, respectively. The author has contributed to research in topic(s): Spontaneous emission & Light-emitting diode. In a tandem cell conguration constructed from a single material, one can achieve two dierent eective bandgaps, thereby exceeding the ShockleyQueisser limit. The origin of high efficiency in low-temperature solution-processable bilayer organometal halide hybrid solar cells. Green, M. A., Emery, K., Hishikawa, Y., Warta, W. & Dunlop, E. D. Solar cell efficiency tables (Version 45). Detailed balance limit of the efficiency of tandem solar-cells. The slightly lower FFs for the devices fabricated on AgNWs as compared with the ITO counterparts can be ascribed to the higher series resistance (RS), probably resulting from the contact resistance between the AgNWs and ZnO. Considering the spectrum losses alone, a solar cell has a peak theoretical efficiency of 48% (or 44% according to Shockley and Queisser their "ultimate efficiency factor"). To push the performances of these solar technologies beyond the ShockleyQueisser limit, several approaches have been proposed, for instance, up-conversion3, multi-junction configuration4,5,6, multiple exciton generation7,8 and concentrator cells, and so on. Taking advantage of the fact that parallel-connection does not require current matching, and therefore balancing the current flow in the bottom series-tandem DPPDPP cells is of critical significance. (a) Device architecture of inverted solar cells with AgNW bottom electrode. The curve is wiggly because of IR absorption bands in the atmosphere. The transmittance spectrum of ZnO/N-PEDOT, the first intermediate layer, is depicted in Fig. The calculated bandgap required for the semiconductor to achieve the Shockley-Queisser limit is 1.34 eV , which is higher than the average band gap of perovskite materials. J. Appl. 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. The Shockley-Queisser-limit is a theoretical limit for solar cells. where If the band gap is too high, most daylight photons cannot be absorbed; if it is too low, then most photons have much more energy than necessary to excite electrons . Sci. Kim, J. Y. et al. For series-connected tandem solar cells, the essential component is to construct an efficient intermediate layer serving as charge recombination zone for electrons and holes generated from subcells6,18,19,20,21,22,23,24,25. 4c confirms a well-organized layer stack. High fill factors up to 68% without resistive losses are achieved for both organic and hybrid triple-junction devices. A major loss factor is related to the energy mismatch between the broad wavelength distribution of sunlight and the mono-band gap of . 2). The semitransparent perovskite device shows a JSC=16.28mAcm2, VOC=0.94V and FF=65.6%, yielding a PCE of 10.04%. A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells. You are using a browser version with limited support for CSS. Similar simulation results for the triple-junction DPPDPP/OPV12 devices are presented in Supplementary Fig. Energy Mater. Energy Environ. From a practical point of view, however, the PP interconnection is too complex to process due to the necessity of introducing two transparent intermediate electrodes. (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. 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. : . 172054 and No. By integrating series- and parallel-interconnections into a triple-junction configuration, we find significantly relaxed material selection and current-matching constraints. Adebanjo, O. et al. where Vs is the voltage equivalent of the temperature of the sun. Since these can be viewed as the motion of a positive charge, it is useful to refer to them as "holes", a sort of virtual positive electron. For example, one photon with more than double the bandgap energy can become two photons above the bandgap energy. J. Appl. Prog. 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. If a very efficient system were found, such a material could be painted on the front surface of an otherwise standard cell, boosting its efficiency for little cost. Secondly, reflectance of the material is non-zero, therefore absorbance cannot be 100% above the band gap. In other words, photons of red, yellow and blue light and some near-infrared will contribute to power production, whereas radio waves, microwaves, and most infrared photons will not. Together with the high FF of 64.5% and VOC of 0.95V, the hybrid triple-junction device shows a PCE value of 11.34%, corresponding to a PCE enhancement by 12.5%. Luque, A., Marti, A. These results demonstrated the excellent functionality of the ZnO/N-PEDOT intermediate layer in the series-connected tandem architecture. 2, the absorption profiles of the two active layers are complementary with that of DPP:PC60BM, suggesting they are appropriate material combinations for manufacturing multi-junction devices. Illumination was provided by a solar simulator (Oriel Sol 1 A from Newport) with AM1.5G spectrum and light intensity of 100mWcm2, which was calibrated by a certified silicon solar cell. Provided by the Springer Nature SharedIt content-sharing initiative. A generic concept to overcome bandgap limitations for designing highly efficient multi-junction photovoltaic cells. 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. (b,c) Typical JV curves of single-junction reference cells of PCDTBT:PC70BM (b) and OPV12:PC60BM (c) deposited on ITO and AgNWs-coated glass substrates. The authors derive the equation, which can be solved to find zm, the ratio of optimal voltage to thermal voltage. Li, N. et al. Electron. In practice, however, this conversion process tends to be relatively inefficient. 5a, illustrating the interplay of the photocurrent generation in the three subcells. All the materials were used as received without further purification. performed the optical simulations. We would like to thank Cambrios Technology Corporation, Dr Mathieu Turbiez from BASF and Dr Norman Lchinger from Nanograde for the supply of AgNWs, DPP and ZnO dispersion, respectively. Solution-processed parallel tandem polymer solar cells using silver nanowires as intermediate electrode. To evaluate the as-designed recombination contacts, series-connected reference tandem cells using DPP:PC60BM as two identical active layers (denoted as DPPDPP) were first constructed. C.O.R.Q., C.B. The record efficiencies of several types of solar. F.W.F. 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. Energy Mater. For very low illumination, the curve is more or less a diagonal line, and m will be 1/4. If the resistance of the load is too high, the current will be very low, while if the load resistance is too low, the voltage drop across it will be very low. 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. 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. We chose silver nanowires (AgNWs) as the intermediate electrode for our triple-junction devices because of their high transparency and low sheet resistance as well as the facile solution processability26,27,28,29,30. CAS The light intensity at each wavelength was calibrated with a standard single-crystal Si solar cell. 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. We show a material bandgap of 1.82-1.96 eV to allow a limiting 51-57% PCE for a single-junction device under various indoor illuminations. You, J. 10.5% efficient polymer and amorphous silicon hybrid tandem photovoltaic cell. 32, 236241 (2007) . Here we report a generic concept to alleviate this limitation. Chem. 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). }, where 18, 789794 (2006) . [28], Another possibility for increased efficiency is to convert the frequency of light down towards the bandgap energy with a fluorescent material. In silicon, this transfer of electrons produces a potential barrier of about 0.6 V to 0.7 V.[6], When the material is placed in the sun, photons from the sunlight can be absorbed in the p-type side of the semiconductor, causing electrons in the valence band to be promoted in energy to the conduction band. Mater. Hendriks, K. H., Li, W. W., Wienk, M. M. & Janssen, R. A. J. Small-bandgap semiconducting polymers with high near-infrared photoresponse. = Successively, an electron extraction layer of ZnO was deposited on top of AgNWs using the same parameters, followed by blading the third active blend of PCDTBT:PC70BM at 60C. This process is known as photoexcitation. Optimal Location of the Intermediate Band Gap Energy in the Intermediate Band Solar Cell Previous search for low-bandgap (1.2 to 1.4 eV) halide perovskites has resulted in several candidates, but all are hybrid organic-inorganic compositions, raising potential concern regarding . 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Typical JV characteristics of the as-prepared single-junction devices are displayed in Fig. Google Scholar. Nano Lett. In silicon this reduces the theoretical performance under normal operating conditions by another 10% over and above the thermal losses noted above. He . 4b. In addition, as indicated in Supplementary Fig. (At that value, 22% of the blackbody radiation energy would be below the band gap.) : John Wiley & Sons, 2011. Appl. {\displaystyle I_{0}=2qt_{c}Q_{c}/f_{c}. By submitting a comment you agree to abide by our Terms and Community Guidelines. 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. (q being the charge of an electron). Other recombination processes may also exist (see "Other considerations" below), but this one is absolutely required. These PCE losses are mainly attributed to the relatively low VOC of triple-junction that is close to the top subcells, and this suppression can be readily eliminated by employing high-performance top subcells with VOC matched to the bottom series-connected subcells. On this Wikipedia the language links are at the top of the page across from the article title. If, however, the intense light heats up the cell, which often occurs in practice, the theoretical efficiency limit may go down all things considered. Beiley, Z. M. & McGehee, M. D. Modeling low cost hybrid tandem photovoltaics with the potential for efficiencies exceeding 20%. Science 334, 15301533 (2011) . Phys. Another important contributor to losses is that any energy above and beyond the bandgap energy is lost. These factors include the relative cost per area of solar cells versus focusing optics like lenses or mirrors, the cost of sunlight-tracking systems, the proportion of light successfully focused onto the solar cell, and so on. 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. Shockley and Queisser calculated that the best band gap for sunlight happens to be 1.1 eV, the value for silicon, and gives a u of 44%. 1.5-1.6 eV bandgap Pb-based perovskite solar cells (PSCs) with 30-31% theoretical efficiency limit by the Shockley-Queisser model achieve 21-24% power conversion efficiencies (PCEs). This relies on a practical IR cell being available, but the theoretical conversion efficiency can be calculated. However, the stringent current-matching criterion presents primarily a material challenge and permanently requires developing and processing novel semiconductors with desired bandgaps and thicknesses. Triple junction polymer solar cells. ACS Appl. 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. 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. It is worth mentioning that we have employed a simple modified doctor blading technique to coat the AgNW electrode16, which enables the deposition of the NW film in a stripe and thereby eliminates any subsequent patterning steps. (a) Equivalent electronic circuit of the series/series (SS) triple-junction organic solar cells. Photonics 6, 180185 (2012) . Kojima, A., Teshima, K., Shirai, Y. would like to acknowledge the funding from the China Scholarship Council and the Joint Project Helmholtz-Institute Erlangen Nrnberg (HI-ERN) under project number DBF01253, respectively. Enjoy! This is why the efficiency falls if the cell heats up. Thus the rate of recombination, in this model, is proportional to exp(V/Vc) times the blackbody radiation above the band-gap energy: (This is actually an approximation, correct so long as the cell is thick enough to act as a black body, to the more accurate expression[7][8], The difference in maximum theoretical efficiency however is negligibly small, except for tiny bandgaps below 200meV. BC8 . These observations provide sufficient evidence that there are no resistive losses for the intermediate AgNW electrode in terms of collecting charge carriers. {\displaystyle I_{0}[\exp(V/V_{c})-1]. 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. 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. Solar cells based on quantum dots: Multiple exciton generation and intermediate bands. It can be seen that the two triple-junction cells achieved JSC of 9.67mAcm2 (DPPDPP/PCDTBT) and 9.55mAcm2 (DPPDPP/OPV12) which is in good agreement with the optical simulations. [9]), The rate of generation of electron-hole pairs not due to incoming sunlight stays the same, so recombination minus spontaneous generation is, I 26, 67786784 (2014) . One can then use the formula. 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.