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Now showing items 1 - 16 of 282

  • Directly Photoexcited Oxides for Photoelectrochemical Water Splitting

    Pan, Linfeng   Vlachopoulos, Nick   Hagfeldt, Anders  

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  • SnS Quantum Dots as Hole Transporter of Perovskite Solar Cells

    Li, Yang   Wang, Zaiwei   Ren, Dan   Liu, Yuhang   Zheng, Aibin   Zakeeruddin, Shaik M.   Dong, Xiandui   Hagfeldt, Anders   Grätzel, Michael   Wang, Peng  

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  • Guanine-Stabilized Formamidinium Lead Iodide Perovskites

    Hong, Li   Milic, Jovana   Ahlawat, Paramvir   Mladenovic, Marko   Kubicki, Dominik J.   Jahanbakhshi, Farzaneh   Ren, Dan   Gelvez-Rueda, Maria   Ruiz-Preciado, Marco A.   Ummadisingu, Amita   Liu, Yuhang   Tian, Chengbo   Pan, Linfeng   Zakeeruddin, Shaik M.   Hagfeldt, Anders   Grozema, Ferdinand C.   Rothlisberger, Ursula   Emsley, Lyndon   Han, Hongwei   Grätzel, Michael  

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  • Dye sensitized photoelectrolysis cells

    Yun, Sining   Vlachopoulos, Nick   Qurashi, Ahsanulhaq   Ahmad, Shahzada   Hagfeldt, Anders  

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  • Solid-State Dye-Sensitized Solar Cells

    Zhang, Jinbao   Freitag, Marina   Hagfeldt, Anders   Boschloo, Gerrit  

    The conventional liquid dye-sensitized solar cell (l-DSC) is a photoelectrochemical system with a liquid redox electrolyte. Replacement of the liquid electrolyte with a solid-state hole transporting material (HTM) has several advantages: dye desorption is prevented, liquid leakage or evaporation cannot occur, and, finally, a solid-state device is made, which is easier to encapsulate and to series-connect. Thus far, solid-state dye-sensitized solar cell (ssDSC) are lagging behind in terms of power conversion efficiencies compared to the l-DSC, but recent advances in dyes and hole conducting materials, leading to ssDSC with 11% efficiency, suggest that this gap will soon be closed.
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  • Photobatteries and Photocapacitors

    Vlachopoulos, Nick   Hagfeldt, Anders  

    This chapter is dedicated to the interfacing of dye-sensitized solar cells (DSSCs) and electrochemical energy storage cells. After a brief introduction to the basic principles of useful and deleterious reactions at the photoelectrode, as related to the analysis of the present chapter, and to the necessary terminology, photobatteries are discussed, of which two main types can be distinguished: these based solely on redox reactions in solution, usually with the necessity for external storage of the solutions, due to the low energy density of the electrolyte solutions, and these incorporating solid energy storage materials with high energy density, e.g., metals, metal oxides or electronically conducting polymers, in one of the electrodes. In addition to the most common three-electrode model, alternative two-electrode and four-electrode (two separate cells in series) systems are presented. Subsequently, photocapacitors are introduced. After a presentation of the basic concepts of electrochemical supercapacitor concepts and operation, the two basic types of photocapacitor, that of two and three-electrode, are presented, with a discussion of the disadvantages of the first type, despite the construction simplicity, as compared to the second one. In the latter, light is harvested by a DSSC, based either on a liquid electrolyte containing a redox mediator or a solid hole conductor, juxtaposed to a capacitor based on carbon, metal oxide or conducting polymer electrodes. For both photobatteries and photocapacitors several systems are discussed, with the various processes at and between the electrodes presented in detail. Moreover, the various formulas for the calculation of energy storage efficiency are explained.
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  • Morphological and compositional progress in halide perovskite solar cells

    Kim, Hui-Seon   Hagfeldt, Anders   Park, Nam-Gyu  

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  • Novel p-dopant toward highly efficient and stable perovskite solar cells

    Seo, Ji-Youn   Kim, Hui-Seon   Akin, Seckin   Stojanovic, Marko   Simon, Elfriede   Fleischer, Maximilian   Hagfeldt, Anders   Zakeeruddin, Shaik M.   Graetzel, Michael  

    Li-TFSI is the most common p-dopant for the hole conductor spiro-MeOTAD in the normal structure (n-i-p) of perovskite solar cells (PSCs), which consistently yield the highest power conversion efficiency (PCE) albeit at the risk of lower long-term operational stability. Here we successfully replace conventional Li-TFSI with Zn-TFSI2, which not only acts as a highly effective p-dopant but also enhances considerably both the photovoltaic performance and long-term stability. The incorporation of Zn-TFSI2 as a dopant for spiro-MeOTAD leads to an increase by one order in the hole mobility compared to Li-TFSI from 3.78 x 10(-3) cm(2) V-1 s(-1) to 3.83 x 10(-2) cm(2) V-1 s(-1). Furthermore, the device with Zn-TFSI2 showed an 80 mV higher built-in voltage and a bigger recombination resistance than the one with Li-TFSI, which were responsible for the striking increase in both the open-circuit voltage and fill factor, leading to a stabilized PCE of 22.0% for the best cells. Remarkably, the device employing Zn-TFSI2 demonstrated superb photo-stability, showing even a 2% increase in the PCE after 600 h light soaking at the maximum power point (mpp) under full sun, while the PCE of the device with Li-TFSI decreased by 20% under the same conditions. Similarly, the device with Zn-TFSI2 showed better operational stability at 50 degrees C resulting in a 21% decrease in the PCE after 100 h aging at the mpp under full sun while the Li-TFSI based one showed a 55% decrease. Moreover, the Zn-TFSI2 based device was capable of effectively resisting humidity compared to the one based on Li-TFSI from shelf stability monitoring (R.H. 40%) in the dark.
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  • Theoretical Treatment of CH3NH3PbI3 Perovskite Solar Cells

    Yun, Sining   Zhou, Xiao   Even, Jacky   Hagfeldt, Anders  

    Hybrid halide perovskite solar cells (PSCs) giving over 22% power conversion efficiencies (PCEs) have attracted considerable attention. Although perovskite plays a significant role in the operation of PSCs, the fundamental theories associated with perovskites have not been resolved in spite of the increase in research. In this Minireview, we assess the current understanding, based on the first-principles calculations, of structural and electronic properties, defects, ionic diffusion, and shift current for CH3NH3PbI3 perovskite, and the effect of ionic transport on the hysteresis of current-voltage curves in PSCs. The shift current connected to the possible presence of ferroelectricity is also discussed. The current state-of-the-art and some open questions regarding PSCs are also highlighted, and the benefits, challenges, and potentials of perovskite for use in PSCs are stressed.
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  • Perovskite solar cell - electrochemical double layer capacitor interplay

    Intermite, Stefania   Arbizzani, Catia   Soavi, Francesca   Gholipour, Somayeh   Turren-Cruz, Silver-Hamill   Correa-Baena, Juan Pablo   Saliba, Michael   Vlachopoulos, Nickolaos   Ali, Abdollah Morteza   Hagfeldt, Anders   Graetzel, Michael  

    We demonstrate that by a proper design of a system comprising a perovskite solar cell (PSC) coupled to an electrochemical double-layer capacitor (EDLC), it is possible to simultaneously improve both the PSC and EDLC performance and outperform each single unit behavior. Specifically, we propose a parallel connection of PSC and EDLC of different size. The EDLC buffers PSC fluctuations by storing the converted solar energy permitting for very high power output (increased by 1 order of magnitude). At the same time, the PSC improves the capacitive response of the EDLC that can be downsized towards system miniaturization. (C) 2017 Elsevier Ltd. All rights reserved.
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  • Phase stabilization of all-inorganic perovskite materials for photovoltaics

    Xiang, Wanchun   Hagfeldt, Anders  

    Cubic phase stabilization is extremely important for the application of cesium lead halide inorganic perovskite materials into fabrication of perovskite solar cells. Methods on how to stabilize inorganic perovskite phase have been discussed in this review. The increase of surface energy of perovskite grains can stabilize the cubic perovskite phase simply by decreasing the grain size or reducing the dimension of perovskite crystals. The substitution of cations or anions in the perovskite crystal lattice by different elements, followed by the rule of Goldschmidt tolerance factor, can also produce stable inorganic perovskites with enhanced electronic and optical properties. Meanwhile, an abundant choice of appropriate elements for the substitution can fundamentally enrich the library of stable inorganic perovskites.
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  • Elucidating the role of chlorine in perovskite solar cells

    Fan, Lin   Ding, Yi   Luo, Jingshan   Shi, Biao   Yao, Xin   Wei, Changchun   Zhang, Dekun   Wang, Guangcai   Sheng, Yun   Chen, Yifeng   Hagfeldt, Anders   Zhao, Ying   Zhang, Xiaodan  

    It has been proposed that introducing the chlorine anion into a CH3NH3PbI3 perovskite material can substantially improve the materials properties as well as the solar cell performance. To elucidate the role of chlorine in perovskite solar cells (PSCs), here we introduced PbCl2 into the precursor, and studied the chlorine configuration evolution during perovskite film formation and the associated influence on PSC performance in detail. We found that chlorine could be successfully incorporated into the precursor film in the form of PbICl or PbCl2 through a properly designed preparation, and it was conserved in the final perovskite film with a configuration of MAPbCl(3), PbICl or PbCl2 depending on the fabrication process. However, no evidence of a MAPbI(3-x)Cl(x) phase was observed, and it is considered that MAPbI(3-x)Cl(x) might be metastable or possesses a higher formation energy. In addition, we demonstrate that the formation of a porous PbICl scaffold in the precursor film plays a key role in high quality perovskite film realization, benefiting from an effective stress release during structure expansion after methylammonium iodide dripping. Moreover, we propose that residual amorphous PbCl2 can effectively passivate defects in perovskite film, and dramatically improve the film's electrical properties. Finally, n-i-p type planar PSCs with efficiencies up to 19.45% were achieved. It should be mentioned that the whole process for the formation of the PSCs is performed at less than 100 degrees C, which is beneficial for a wide range of applications, such as flexible and tandem solar cells.
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  • Proof-of-concept for facile perovskite solar cell recycling

    Kadro, Jeannette M.   Pellet, Norman   Giordano, Fabrizio   Ulianov, Alexey   Muntener, Othmar   Maier, Joachim   Gratzel, Michael   Hagfeldt, Anders  

    Perovskite solar cells based on CH3NH3PbI3 and related materials have reached impressive efficiencies that, on a lab scale, can compete with established solar cell technologies, at least in short-term observations. Despite frequently voiced concerns about the solubility of the lead salts that make up the absorber material, several life cycle analyses have come to overall positive conclusions regarding the environmental impact of perovskite solar cell (PSC) production. Their particularly short energy payback time (EBPT) in comparison to other established PV technologies makes them truly competitive. Several studies have identified valuable components such as FTO, gold and high temperature processes as the most significant contributors to the environmental impact of PSCs. Considering these findings, we have developed a rapid dismantling process allowing the recovery of all major components, saving raw materials, energy and production time in the fabrication of recycled PSCs. We demonstrate that the performance of PSCs fabricated from recycled substrates can compete with that of devices fabricated from virgin materials.
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  • Supramolecular Hemicage Cobalt Mediators for Dye-Sensitized Solar Cells.

    Freitag, Marina   Yang, Wenxing   Fredin, Lisa A   D'Amario, Luca   Karlsson, K Martin   Hagfeldt, Anders   Boschloo, Gerrit  

    A new class of dye-sensitized solar cells (DSSCs) using the hemicage cobalt-based mediator [Co(ttb)]2+/3+ with the highly preorganized hexadentate ligand 5,5'',5''''-((2,4,6-triethyl benzene-1,3,5-triyl)tris(ethane-2,1-diyl))tri-2,2'-bipyridine (ttb) has been fully investigated. The performances of DSSCs sensitized with organic D-pi-A dyes utilizing either [Co(ttb)]2+/3+ or the conventional [Co(bpy)3 ]2+/3+ (bpy=3D2,2'-bipyridine) redox mediator are comparable under 1000=E2=80=85Wm-2 AM 1.5=E2=80=85G illumination. However, the hemicage complexes exhibit exceptional stability under thermal and light stress. In particular, a 120-hour continuous light illumination stability test for DSSCs using [Co(ttb)]2+/3+ resulted in a 10% increase in the performance, whereas a 40% decrease in performance was found for [Co(bpy)3 ]2+/3+ electrolyte-based DSSCs under the same conditions. These results demonstrate the great promise of [Co(ttb)]2+/3+ complexes as redox mediators for efficient, cost-effective, large-scale DSSC devices. =C2=A9 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim.
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  • On the Mechanistic Understanding of Photovoltage Loss in Iron Pyrite Solar Cells

    Rahman, Mohammad   Boschloo, Gerrit   Hagfeldt, Anders   Edvinsson, Tomas  

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  • Photon Energy-Dependent Hysteresis Effects in Lead Halide Perovskite Materials

    Pazoki, Meysam   Jacobsson, T. Jesper   Cruz, Silver H. T.   Johansson, Malin B.   Imani, Roghayeh   Kullgren, Jolla   Hagfeldt, Anders   Johansson, Erik M. J.   Edvinsson, Tomas   Boschloo, Gerrit  

    Lead halide perovskites have a range of spectacular properties and interesting phenomena and are a serious candidate for the next generation of photovoltaics with high efficiencies and low fabrication costs. An interesting phenomenon is the anomalous hysteresis often seen in current-voltage scans, which complicates accurate performance measurements but has also been explored to obtain a more comprehensive understanding of the device physics. Herein, we demonstrate a wavelength and illumination intensity dependency of the hysteresis in state-of-the-art perovskite solar cells with 18% power conversion efficiency (PCE), which gives new insights into ion migration. The perovskite devices show lower hysteresis under illumination with near band edge (red) wavelengths compared to more energetic (blue) excitation. This can be rationalized with thermalization-assisted ion movement or thermalization-assisted vacancy generation. These explanations are supported by the dependency of the photovoltage decay with illumination time and excitation wavelength, as well as by impedance spectroscopy. The suggested mechanism is that high-energy photons create hot charge carriers that either through thermalization can create additional vacancies or by release of more energetic phonons play a role in overcoming the activation energy for ion movement. The excitation wavelength dependency of the hysteresis presented here gives valuable insights into the photophysics of the lead halide perovskite solar cells.
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