| 1. |
- Cui, Yong, et al.
(författare)
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Single-Junction Organic Photovoltaic Cells with Approaching 18% Efficiency
- 2020
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 32:19
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Tidskriftsartikel (refereegranskat)abstract
- Optimizing the molecular structures of organic photovoltaic (OPV) materials is one of the most effective methods to boost power conversion efficiencies (PCEs). For an excellent molecular system with a certain conjugated skeleton, fine tuning the alky chains is of considerable significance to fully explore its photovoltaic potential. In this work, the optimization of alkyl chains is performed on a chlorinated nonfullerene acceptor (NFA) named BTP-4Cl-BO (a Y6 derivative) and very impressive photovoltaic parameters in OPV cells are obtained. To get more ordered intermolecular packing, the n-undecyl is shortened at the edge of BTP-eC11 to n-nonyl and n-heptyl. As a result, the NFAs of BTP-eC9 and BTP-eC7 are synthesized. The BTP-eC7 shows relatively poor solubility and thus limits its application in device fabrication. Fortunately, the BTP-eC9 possesses good solubility and, at the same time, enhanced electron transport property than BTP-eC11. Significantly, due to the simultaneously enhanced short-circuit current density and fill factor, the BTP-eC9-based single-junction OPV cells record a maximum PCE of 17.8% and get a certified value of 17.3%. These results demonstrate that minimizing the alkyl chains to get suitable solubility and enhanced intermolecular packing has a great potential in further improving its photovoltaic performance.
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| 2. |
- Liu, Jinghuang, et al.
(författare)
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Effect of iodine doping on photoelectric properties of perovskite-based MOS devices
- 2020
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Ingår i: Materials letters (General ed.). - : ELSEVIER. - 0167-577X .- 1873-4979. ; 261
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Tidskriftsartikel (refereegranskat)abstract
- In this article, the PVK based metal-oxide-semiconductor (MOS) capacitor structures were fabricated and the photoelectric performance of the capacitor was carried out to study the intrinsic electrical characteristic of PVK with iodine doped. The electrical hysteresis of the capacitor after iodine doping becomes larger in the dark state, which indicates that the hysteresis behavior of the PVK is caused by the mobile iodine ions. The photocurrent of iodine-doped PVK is significantly greater than that of undoped PVK under illumination, which suggests that the capacitor has better response to light and the photodetectors efficiency also increase after iodine doping. Our results provide a theoretical basis for the potential application of memory devices such as memristors under dark. Meanwhile, it provides a method to improve photodetector performance by adding an appropriate amount of iodine to the PVK precursor solution. (C) 2019 Elsevier B.V. All rights reserved.
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| 3. |
- Pang, Tiqiang, et al.
(författare)
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Hysteresis effects on carrier transport and photoresponse characteristics in hybrid perovskites
- 2020
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Ingår i: Journal of Materials Chemistry C. - : ROYAL SOC CHEMISTRY. - 2050-7526 .- 2050-7534. ; 8:6, s. 1962-1971
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Tidskriftsartikel (refereegranskat)abstract
- Organic-inorganic hybrid perovskites have recently emerged as promising potential candidate materials in the area of photoelectrics due to their unparalleled optoelectronic features. However, the performance of an optoelectronic device is always affected by the mixed ionic and electronic conducting behavior within perovskites. Herein, the hysteresis effect on carrier mobility and photoresponse characteristics of perovskites were investigated through adding rational additives to the precursor solution. The results show that the perovskite with foreign fullerene derivative (PCBM) additive can suppress hysteresis behavior and increase the mobility by two-fold, while the perovskite with native iodine (I) additive will amplify hysteresis and reduce the mobility by two orders of magnitude at the room temperature compared with that of the pure perovskite. Furthermore, we found that the response characteristics of the photodetectors are strongly affected by the carrier mobility. Capacitance-voltage results confirm the significant change in hysteresis after the introduction of different additives, which explains the changes in mobility and photoresponse time. Our results enlighten the hysteresis effect related to carrier transport and photoresponse characteristics, and provide guidance for the development of reliable, high performance perovskite devices.
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| 4. |
- Wang, Yuming, 1989-
(författare)
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Voltage Losses in Non-fullerene Organic Solar Cells
- 2020
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Non-fullerene acceptors have significantly boosted the efficiencies of organic solar cells (OSCs) in the past few years. State-of-the-art OSCs have achieved a certificated power conversion efficiency of 17.4%. In spite of significant professes, there is still a gap between efficiencies of OSCs and those of traditional inorganic solar cells and emerging perovskite solar cells. One of the important reasons for this gap is the large voltage losses for OSCs. Understanding and reducing the voltage losses is of critical importance for further improving the performance of the OSCs. This thesis studies the voltage losses of OSCs based on non-fullerene acceptors.The charge transfer (CT) state plays a critical role in the open-circuit voltage (VOC) of the OSCs. According to the reciprocity relation between the electroluminescence (EL) and the external quantum efficiency of solar cells (EQEPV), we know that the sub-bandgap absorbance (responsible for large radiative recombination voltage losses) and the weak emission of CT states (responsible for large non-radiative voltage losses) are the reasons for large voltage losses in fullerene-based OSCs. In addition, the driving force, defined as the difference between the energy of the singlet states and CT states, was considered to be essential for efficient charge generation, especially when the OSC field was dominated by fullerene acceptors. A series of polymer: non-fullerene pairs with different driving forces were studied by spectroscopy methods e.g. Fourier-transfer photocurrent spectroscopy (FTPS) and electroluminescence spectroscopy. It was demonstrated that both radiative recombination voltage loss and the non-radiative energy loss can be suppressed by reducing driving forces, resulting in overall decreased voltage losses of the OSCs.Another question regarding the trade-off between the voltage losses and charge generation is still under debate – is the driving force essential for the efficient charge separation? A novel polymer: non-fullerene system with negligible offsets between both the lowest unoccupied molecular orbital (LUMO) and the highest unoccupied molecular orbital (HOMO) of the donor and acceptor was studied. Although the driving force for the new system is small, it works efficiently. It implies that efficient charge generation can occur with negligible driving forces for both electrons and holes, suggesting that the high VOC and efficient charge generation can be achieved at the same time for non-fullerene OSCs.In addition to binary OSCs, the voltage losses in ternary OSCs are also studied in this thesis. It was found that the VOC of the ternary organic solar cells cannot be well interpreted by the widely used alloy or parallel model. The non-radiative voltage loss, which is not paid much attention in the two models, was found to play an important role in the tunable VOC of the ternary OSCs. We demonstrate that the non-radiative voltage losses in ternary OSCs is dependent on the radiative recombination rates and the energy levels of the CT states of the two constituting binary OSCs. Furthermore, the aggregation of the individual components can be decreased by adding the third component, suppressing the aggregation caused quenching and leading to a reduced non-radiative recombination voltage loss.The non-fullerene based OSCs with small voltage losses show great potential for indoor applications. Although it might be difficult for OSCs to compete with commercial silicon solar cells for harvesting the solar energy, we demonstrate highly efficient and stable non-fullerene OSCs under indoor light, providing a unique application possibility where OSCs can out-compete other photovoltaic technologies. For the indoor application, the OSCs takes advantage of the easily tunable absorption range of the organic semiconductors, and avoids their drawbacks of the instability under strong outdoor light containing ultraviolet light.
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| 5. |
- Xu, Guodong, et al.
(författare)
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Reducing Energy Loss and Morphology Optimization Manipulated by Molecular Geometry Engineering for Hetero-junction Organic Solar Cells
- 2020
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Ingår i: Chinese journal of chemistry. - : WILEY-V C H VERLAG GMBH. - 1001-604X .- 1614-7065. ; 38:12, s. 1553-1559
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Tidskriftsartikel (refereegranskat)abstract
- A Summary of main observation and conclusion Molecular geometry engineering is an effective strategy to control the micromorphology and molecular energy level in organic photovoltaics (OPVs). Two novel copolymers based on alkylsilyl- and chloride-functionalized benzodithiophene (BDT) were designed and synthesized for wide bandgap copolymer donor materials in OPVs. It was found that the two copolymers exhibited distinctly different properties in active layer when blended with fullerene-free acceptor IT-4F. The chloride-functionalized copolymer PBDTCl-TZ with deeper molecular energy level and better coplanar structure induced more ordered aggregation in blend film. Thus, the device based on PBDTCl-TZ exhibits better energy alignment with IT-4F and smaller radiative recombination. Furthermore, the non-radiative recombination of PBDTCl-TZ:IT-4F based device is about 45 mV lower than the PBDTSi-TZ:IT-4F based device, contributing to a lower energy loss (E-loss), and a higher open-circut voltage (V-OC). As a result, the devices based on the blend of PBDTCl-TZ:IT-4F exhibit a high power conversion efficiency (PCE) of up to 12.2% with a highV(OC)of 0.837 V, higher than that of PBDTSi-TZ:IT-4F, of which the PCE is 11.2% with a V-OC of 0.781 V.
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| 6. |
- Yuan, Jun, et al.
(författare)
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Reducing Voltage Losses in the A-DAD-A Acceptor-Based Organic Solar Cells
- 2020
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Ingår i: Chem. - : CELL PRESS. - 2451-9308 .- 2451-9294. ; 6:9, s. 2147-2161
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Tidskriftsartikel (refereegranskat)abstract
- Power conversion efficiencies (PCEs) of solution-processed organic solar cells (OSCs) have recently reached 17.4% (certified) for single-junction devices. Crucial to this advancement is the development of non-fullerene acceptors (NFAs) since 2015. The recent A-DAD-A NFAs have attracted widespread attention because of their ladder-type electron-deficient-core-based central fused ring with improved transport properties and optimum energy levels. With the synergistic effect of electron-deficient-core and specific molecular geometry, the A-DADA molecules could achieve low voltage losses and high current generation at the same time, reaching new regimes of device physics and photophysics. This perspective will discuss the voltage losses in state-of-the-art A-DAD-A NFA-based OSCs and propose new molecular design strategies to achieve PCEs over 20% in OSCs based on these new acceptors by further decreasing their total voltage losses.
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