Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells

Vandewal, Koen; Tvingstedt, Kristofer; Gadisa, Abay; Inganäs, Olle; Manca, Jean

doi:10.1103/physrevb.81.125204

Cited by 791 publications

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References 41 publications

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“…[11,23] ECT, which we estimate by fitting the lower energy part of Fourier-transform photocurrent spectroscopy (FTPS) spectra, which originates from an excitation in the CT manifold. [24,25] We find an ECT ~ 1.26 eV that is largely unaffected by the fullerene ratio (Figure 3c Overall, we obtained a PCE of 4.9 % for devices based on C60, whereas devices based on C70 or the mixture C60:C70 yielded a PCE of 6 %, with champion solar cells of 6.5% for the ternary blend (Table 2). Since the C60:C70 ratio that is obtained during fullerene synthesis can range from 4:1 to about 4:3.2, depending on the preparation route, [10,11] we also tested 5:4:1 PTB7:C60:C70 devices, which yielded a comparably high PCE of 5.1%.…”

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confidence: 75%

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

et al. 2015

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cells 2 / 18Fullerenes are an intriguing class of organic semiconductors that feature a high electron affinity and exceptional charge transport properties, desirable for a number of thin-film optoelectronic applications such as field-effect transistors (FETs) and organic solar cells. Despite their desirable solid-state properties a major disadvantage of pristine C60 and C70 is the seemingly poor solubility in organic solvents, [1,2] which however can be substantially improved by attaching exohedral moieties to the fullerene cage, albeit at the expense of a high electron mobility. [3][4][5] In addition, pristine fullerenes suffer from the strong tendency to crystallize during solvent removal, which complicates formation of continuous thin films. As a result, substituted fullerenes, such as in particular phenyl-Cx-butyric acid methyl esters (PCBMs; x = 61 or 71), are by far the most widely studied electron acceptor material for organic photovoltaic applications. The trade-off between increased solubility and reduced electron mobility has so far been acceptable for thin-film solar cells because the latter is still sufficiently high to not limit solar cell performance, which more strongly depends on the precise active layer nanostructure. However, as future improvements in device efficiency rely on thick active layers and high-mobility materials, [6] the use of pristine fullerenes may prove to be advantageous provided that solubility issues can be addressed and a favorable nanostructure can be achieved.The most efficient active layer nanostructure of organic solar cells is the bulkheterojunction, which is typically prepared by co-processing a fullerene acceptor and a suitable donor from a common organic solvent. Although devices based on the pristine fullerene C70 have been reported for both polymer and small-molecule donors with a powerconversion efficiency PCE of 5.1 % and 5.9 %, respectively, [7,8] the most competitive results are currently achieved with the more soluble PCBMs, which can yield a PCE of more than 10 %. [9] As low cost is the major selling point of organic photovoltaics, it is desirable to choose the most cost-effective materials. In this regard, the use of PCBMs as the electron 3 / 18 acceptor is not optimal. The additional synthesis steps required to prepare these derivatives from pristine fullerenes considerably increase the energy footprint, which implies a higher environmental impact as well as an overall higher materials cost. For instance, Anctil et al.calculated a life cycle embodied energy as low as about 8 GJ kg -1 for the as-synthesized C60:C70 mixture, which increases to 25 GJ kg -1 for C60 and 38 GJ kg -1 for C70 after separation and electronic-grade purification. [10] In contrast, preparation of substituted fullerenes consumes significantly more energy, i.e. 65 GJ kg -1 and 90 GJ kg -1 for electronic-grade PC61BM and PC71BM, respectively. Therefore, the use of pristine fullerenes and in particular C60:C70 mixtures may result in significant energy savings provided that the ability to f...

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Section: / 18mentioning

confidence: 75%

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

et al. 2015

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“…The shift of CT PL emission peak with temperature did not exceed 0.05eV in agreement with previous studies. 54 To study the device-relevant photophysics of TQ1:PC71BM bulk heterojunctions in detail, we fabricated a set of photovoltaic devices and investigated these using CT PL, photocurrent and PPP spectroscopic methods. In addition to the morphology/composition variation we also varied the temperature and the applied external field.…”

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confidence: 99%

Morphology, Temperature, and Field Dependence of Charge Separation in High-Efficiency Solar Cells Based on Alternating Polyquinoxaline Copolymer

et al. 2016

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Charge separation and recombination are key processes determining the performance of organic optoelectronic devices. Here we combine photoluminescence and photovoltaic characterisation of organic solar cell devices with ultrafast multi-pulse photocurrent spectroscopy to investigate charge generation mechanisms in the organic photovoltaic devices based on a blend of an alternating polyquinoxaline copolymer with fullerene. The combined use of these techniques enables the determination of the contributions of geminate and bimolecular processes to the solar cell performance. We observe that charge separation is not a temperature-activated process in the studied materials. At the same time, the generation of free charges shows a clear external-field and morphology dependence. This indicates that the critical step of charge separation involves the non-equilibrium state that is formed at early times after photoexcitation, when the polaronic localisation is not yet complete. This work reveals new aspects of molecular level charge dynamics in the organic light-conversion systems.2 Introduction:

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“…As boundary conditions for our simplified diffusion equation (3) we choose ZnPc excitons reaching the HTL to be reflected (∂n/∂x(x=ZnPc|HTL)=0, details in SI.5) and those reaching C60 to decay immediately into charge transfer (CT) states [16] ( n(x=ZnPc|C60)=0 ) [12] .…”

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Exciton Diffusion Length and Charge Extraction Yield in Organic Bilayer Solar Cells

et al. 2017

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A method for resolving the diffusion length of excitons and the extraction yield of charge carriers is presented based on the performance of organic bilayer solar cells and careful modeling. The technique uses a simultaneous variation of the absorber thickness and the excitation wavelength. Rigorously differing solar cell structures as well as independent photoluminescence quenching measurements give consistent results.

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Relating the open-circuit voltage to interface molecular properties of donor:acceptor bulk heterojunction solar cells

Cited by 791 publications

References 41 publications

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

Morphology, Temperature, and Field Dependence of Charge Separation in High-Efficiency Solar Cells Based on Alternating Polyquinoxaline Copolymer

Exciton Diffusion Length and Charge Extraction Yield in Organic Bilayer Solar Cells

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