Figure 1
Schematic cross section of a tandem organic solar cell comprising two individual cells connected in series via a thin metallic layer.
Source publication
In this study, we have investigated the possibility to realize different types of stacked, serially connected organic solar cells. First of all, we combined solution processed MDMO-PPV:PCBM or P3HT:PCBM and evaporated ZnPc-C60 bulk-heterojunction solar cells to achieved tandem cells exploiting the complementary absorption spectra of each single cel...
Context in source publication
Context 1
... more than single layer solar cell. 14 The fabrication of stacked organic solar cells based on a series connection of two small molecules donor -acceptor heterojunction solar cells has been achieved using an ultrathin metal layer as recombination center between the individual cells. [10][11][12] The structure of such a stacked cell is shown in Fig. 1. If both solar cells comprise the same active material combination, then a doubling of the open-circuit voltage (Voc) is expected. The short circuit current (Isc) corresponds to the lower Isc of the components in the stack. The first cell has to be semitransparent and the film thicknesses have to be adjusted so that both cells will ...
Similar publications
Composition average dependent properties for blends of the conjugated polymer P3HT and the fullerenes [60]PCBM, [60]ICBA and their mixtures were studied using cross-polarization magic-angle-spinning solid-state NMR techniques. We found that the blended fullerenes form an alloy and that when mixed with a third polymer component, the system exhibits...
The performance of organic solar cells consisting of multiple layers, which are a few hundred nanometers thick, is determined by strong optical interference effects. In order to model their optical and photoelectrical behavior, we determined the optical constants of all components of this system. This was done by fitting model dielectric functions...
Organic solar cells based on an interpenetrated network of conjugated polymer as donor and fullerene derivative as acceptor materials have a great potential for improving efficiency. We fabricated a device based on a composite of poly2-methoxy-5-2-ethylhexyloxy-1, 4-phenylenevinylene and 6,6-phenyl C60 butyric acid methyl ester. Surface treatment,...
Citations
... Typically, the devices are stacked on top of each other and connected in series, that is, in a two-terminal approach. Such devices with up to five stacked solar cells have been realized through both vacuum deposition (Hiramoto et al., 1990;Yakimov and Forrest, 2002;Drechsel et al., 2005) and solution processing as well as by combining vacuum and solution processing for the active layers (Colsmann et al., 2006;Prall et al., 2006). The current certified world record for an OSC on a device area exceeding 1 cm 2 is 6.1% for a small molecule-based tandem device (Green et al., 2010). ...
... As a consequence, the latter subcell will be the current-limiting subcell in the tandem device over the entire wavelength range and the EQE of the tandem cell recorded represents the EQE of the current-limiting subcell. [97] This method was applied successfully in characterizing the photocurrent of each subcell independently in tandem devices [43,46,47,90,100] providing accurate evidence for the need to balance the photocurrent of two series connected subcells. [97] In addition, a bias voltage is applied in the bias light EQE measurement to offset the voltage generated by the optically biased subcell, ensuring the subcell under test experiences a net zero voltage bias and to estimate each subcell accurately. ...
... This is the primary advantage of multiple junctions over single junction solar cells since it provides a mechanism by which a larger portion of the solar spectrum can be harvested. In this section, the different types of donor materials used in organic tandem and multi-junction photovoltaic cells are processed from either solution or vacuum evaporation and are listed in Copper phthalocyanine (CuPc) [58, 62-65, 70, 88, 89, 92] Zinc phthalocyanine (ZnPc) [44,45,51,67,71,90,103] Chloroaluminum phthalocyanine (ClAlPc) [53,96] Subnaphthalocyanine (SubNc) [53] Subphthalocyanine (SubPc) [53,96] Fluorinated zinc phthalocyanine derivative (F4-ZnPc) [104] Dicyanovinyl-capped sexithiophene derivative (DCV6T) [104] 2,4-bis[4-(N,N-diphenylamino)-2,6-dihydroxyphenyl] squaraine (DPSQ) [105] 2,7-(9,9-dihexylfluorene)-alt-bithiophene (F6T2) [88] Poly [43,46,59,60] Poly[9,9-didecanefluorene-alt-(bis-thienylene) benzothiadiazole] (PF10TBT) [49] Poly((2,7-(9,9-dioctyl)-fluorene)-alt-5,5-(4',7'-di-2thienyl-2',1',3'-benzothiadiazole)) (PFDTBT) [68] Poly(5,7-di-2-thienyl-2-3-bis(3,5-di(2ethylhexyloxy)phenyl)-thieno [3,4-b]pyrazine) (PTBEHT) [68,76] Poly[3,6-bis(4'-dodecyl-[2,2']bithiophenyl-5-yl)-2,5bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-]pyrrole-1,4dione] (pBBTDPP2) [94,97,102] Poly[2,7-(9,9-didecylfluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothi adiazole)] (PFTBT) [94,97,102] Poly-(3-carboxydithiophene) (P3CT) [87] Poly(carboxyterthiophene-co-diphenylthienopyrazine) (P3CTTP) [87] Poly(2-methoxy-5-2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) [52,101] Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV) [50,86,90] Poly(3-n-hexylthiophene) (P3HT) [43, 44, 46-52, 57, 59-61, 69, 71-73, 75, 89, 90, 93, 95, 98, 106-108] Poly ...
... This is the primary advantage of multiple junctions over single junction solar cells since it provides a mechanism by which a larger portion of the solar spectrum can be harvested. In this section, the different types of donor materials used in organic tandem and multi-junction photovoltaic cells are processed from either solution or vacuum evaporation and are listed in Copper phthalocyanine (CuPc) [58, 62-65, 70, 88, 89, 92] Zinc phthalocyanine (ZnPc) [44,45,51,67,71,90,103] Chloroaluminum phthalocyanine (ClAlPc) [53,96] Subnaphthalocyanine (SubNc) [53] Subphthalocyanine (SubPc) [53,96] Fluorinated zinc phthalocyanine derivative (F4-ZnPc) [104] Dicyanovinyl-capped sexithiophene derivative (DCV6T) [104] 2,4-bis[4-(N,N-diphenylamino)-2,6-dihydroxyphenyl] squaraine (DPSQ) [105] 2,7-(9,9-dihexylfluorene)-alt-bithiophene (F6T2) [88] Poly [43,46,59,60] Poly[9,9-didecanefluorene-alt-(bis-thienylene) benzothiadiazole] (PF10TBT) [49] Poly((2,7-(9,9-dioctyl)-fluorene)-alt-5,5-(4',7'-di-2thienyl-2',1',3'-benzothiadiazole)) (PFDTBT) [68] Poly(5,7-di-2-thienyl-2-3-bis(3,5-di(2ethylhexyloxy)phenyl)-thieno [3,4-b]pyrazine) (PTBEHT) [68,76] Poly[3,6-bis(4'-dodecyl-[2,2']bithiophenyl-5-yl)-2,5bis(2-ethylhexyl)-2,5-dihydropyrrolo[3,4-]pyrrole-1,4dione] (pBBTDPP2) [94,97,102] Poly[2,7-(9,9-didecylfluorene)-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothi adiazole)] (PFTBT) [94,97,102] Poly-(3-carboxydithiophene) (P3CT) [87] Poly(carboxyterthiophene-co-diphenylthienopyrazine) (P3CTTP) [87] Poly(2-methoxy-5-2'-ethyl-hexyloxy)-1,4-phenylene vinylene) (MEH-PPV) [52,101] Poly[2-methoxy-5-(3',7'-dimethyloctyloxy)-p-phenylene vinylene] (MDMO-PPV) [50,86,90] Poly(3-n-hexylthiophene) (P3HT) [43, 44, 46-52, 57, 59-61, 69, 71-73, 75, 89, 90, 93, 95, 98, 106-108] Poly ...
Organic solar cells (OSCs) are widely viewed as one of the key next generation photovoltaic technologies. One strategy to improve the efficiency of OSCs is to enhance the overlap between their absorption spectra and the solar spectrum. Tandem device architectures have been proposed as a means to achieve this strategy because they allow maximum photon capture by the use of photoactive materials that have complimentary absorption. In the work described in this thesis, photocurrent generation pathways, the effect of optical spacers in broad-band single junction devices, and device physics for the operation of tandem OSCs have been investigated in detail. The central results of this research are as follows:
Firstly, photocurrent generation pathways (Channel I and Channel II) were established in the model material systems. During the Channel II process, free charge is generated by the direct absorption of light in the traditional electron acceptor phase. A direct method to distinguish the photocurrent contributions by acceptors such as 70-PCBM in polymer:fullerene blends has been developed and be used to prove that the Channel II mechanism is an important photocurrent creation pathway for complementary acceptor-donor junctions.
Secondly, light trapping and optical field confinement in layered device structures were investigated using optical spacer layers. For this purpose, a ZnO layer was introduced into broad-band single junction OSCs. This helped to identify the advantageous role of the optical spacer in OSCs with an active layer <60 nm in thickness. For devices with a thick active layer (>90 nm), the optical spacer showed no positive effect on the performance of single junction devices with broad-band absorption due to the conflicting nature of optical field distribution at short and long wavelengths. However, the devices with ZnO spacers still displayed better efficiencies arising from the electron transporting and hole-blocking properties of ZnO layers.
Lastly, tandem OSCs connected in series through an Al/MoOX layer were fabricated and their performance optimized by varying the subcell thicknesses. Tandem device performance was found to be strongly dependent on the short circuit current (JSC) and the fill factor (FF) of the two individual subells. The tandem FF was found to be close to that of the photocurrent limiting subcell and the tandem JSC is observed to be close to that of the subcell with higher FF. To accurately characterise each subcell independently, it was determined that close attention should be paid to the photocurrent difference between the two subcells in monochromatic bias light external quantum efficiency measurements. The narrow optical gap polymer in tandem architectures behaves better than that in single junction architectures, owing to the efficient charge collection. Finally, an optimized tandem device was presented with power conversion efficiency greater than its individual subcells.
Moritz Riede studied physics at the University of Cambridge, United Kingdom, where he received his MSc degree in 2002. He obtained his PhD degree from the University of Konstanz in 2006 for research carried out at the Fraunhofer-Institut für Solare Energiesysteme and the Freiburger Materialforschungszentrum FMF. The focus of his thesis was on solution-processed organic solar cells. After his PhD he joined the research group of Prof. Leo at the Institut für Angewandte Photophysik (IAPP) of the Technische Universität Dresden in 2007, where he is now head of the Organic Solar Cell Group. His research concentrates on small-molecule-based organic solar cells, their fundamental working principles, and strategies for device optimization.
In this chapter, we tried to bring out the role of organic and polymer chemistry to provide the much needed support in the development of organic photovoltaic (OPVs) devices with the new and fundamental researches on novel materials with tailor-made properties. A good understanding on the excited state reactivity of photoactive materials would help to prepare new materials and molecules capable of absorbing light over a given wavelength range and using it for driving energy or electron transfer. Scientifically and technologically well equipped chemistry community has explored the possibilities of developing and optimizing the charge separation in the light-harvesting architectures, however it is yet to bear fruit due to the difficulty of transportation of electrons and holes to the corresponding electrodes. Modeling charge mobility in organic semiconductors is complicated due to the presence of bulk heterogeneity in the macrostructure. The understanding of the interface between the metal electrode and the organic material, where charge collection takes place, is even more intriguing. In this chapter, we have highlighted the key features which enable to design new materials for the vast landscape of solar energy conversion and the some of our efforts towards material synthesis for OPVs.
In this article, we review general approaches, challenges and solutions, as well as latest research progress, in the field of polymer tandem solar cells. Despite many limiting factors ranging from processing issues to characterization issues, it has been shown that high efficiency and in-depth understanding of tandem cell operation can be achieved via smart device design and analysis, and interface engineering. We further discuss in detail the operation principles and design rules of polymer tandem cells, revealing a bright future to reach double-digit power conversion efficiency from polymer tandem cells.
The rapidly expanding field of polymer and organic solar cells is reviewed in the context of materials, processes and devices that significantly deviate from the standard approach which involves rigid glass substrates, indium-tin-oxideelectrodes, spincoated layers of conjugated polymer/fullerene mixtures and evaporated metal electrodes in a flat multilayer geometry. It is likely that significant advances can be found by pursuing many of these novel ideas further and the purpose of this review is to highlight these reports and hopefully spark new interest in materials and methods that may be performing less than the current state-of-the-art in their present form but that may have the potential to outperform these pending a larger investment in effort.
Multiple junction solar cells incorporating polymer:fullerene bulk heterojunctions as active layers and solution processed electron and hole transport layers are presented. The recombination layer, deposited between the active layers, is fabricated by spin coating ZnO nanoparticles from acetone, followed by spin coating neutral pH poly(3,4-ethylenedioxythiophene) from water and short UV illumination of the completed device. The key advantage of this procedure is that each step does not affect the integrity of previously deposited layers. The open-circuit voltage (Voc) for double and triple junction solar cells is close to the sum of the Voc’s of individual cells.
Organic photodetectors for use in medical x-ray digital imaging applications are fabricated from poly(3-hexylthiophene) and [6,6]-phenyl C61-butyric acid methyl ester using a solution-based, temperature assisted deposition protocol. In comparison to bulk heterojunction structures, the proposed protocol leads to much lower dark currents while still offering useful external quantum efficiency values. Devices made by this protocol lead to dark currents of around 50 pA/cm2 at −0.8 V, well within the requirements for x-ray digital imaging. When coupled to a scintillating phosphor screen the device yields a linear response of photocurrent to x-ray exposure (from 0 to 7mGy/s) for a range of operating biases.
