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- 2019
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Tidskriftsartikel (refereegranskat)
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| 2. |
- Xie, Shenkun, et al.
(författare)
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Effects of Nonradiative Losses at Charge Transfer States and Energetic Disorder on the Open-Circuit Voltage in Nonfullerene Organic Solar Cells
- 2018
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Ingår i: Advanced Functional Materials. - : WILEY-V C H VERLAG GMBH. - 1616-301X .- 1616-3028. ; 28:5
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Tidskriftsartikel (refereegranskat)abstract
- The considerable improvement on the power conversion efficiency (PCE) for emerging nonfullerene polymer solar cells is still limited by considerable voltage losses that have become one of the most significant obstacles in further boosting desired photovoltaic performance. Here, a comprehensive study is reported to understand the impacts of charge transport, energetic disorder, and charge transfer states (CTS) on the losses in open-circuit voltage (V-oc) based on three high performing bulk heterojunction solar cells with the best PCE exceeding 11%. It is found that the champion poly[(2,6-(4,8-bis(5-(2-ethylhexyl)thiophen-2-yl)benzo[1,2-b:4,5-b]dithiophene)-co-(1,3-di(5-thiophene-2-yl)-5,7-bis(2-ethylhexyl)-benzo[1,2-c:4,5-c]dithiophene-4,8-dione))] (PBDB-T):IT-M solar cell (PCE = 11.5%) is associated with the least disorder. The determined energetic disorder in part reconciles the difference in V-oc between the solar cells. A reduction is observed in the nonradiative losses (V-nonrad) coupled with the increase of energy of CTS for the PBDB-T:IT-M device, which may be related to the improved balance in carrier mobilities, and partially can explain the gain in V-oc. The determined radiative limit for V-oc combined with the V-nonrad generates an excellent agreement for the V-oc with the experimental values. The results suggest that minimizing the energetic disorder related to transport and CTS is critical for the mitigation of V-oc losses and improvements on the device performance.
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| 3. |
- Xu, Yalong, et al.
(författare)
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Simultaneously Improved Efficiency and Stability in All-Polymer Solar Cells by a P-i-N Architecture
- 2019
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Ingår i: ACS Energy Letters. - : AMER CHEMICAL SOC. - 2380-8195. ; 4:9, s. 2277-2286
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Tidskriftsartikel (refereegranskat)abstract
- All-polymer organic solar cells offer exceptional stability. Unfortunately, the use of bulk heterojunction (BHJ) structure has the intrinsic challenge to control the side-chain entanglement and backbone orientation to achieve sophisticated phase separation in all-polymer blends. Here, we revealed that the P-i-N structure can outperform the BHJ ones with a nearly 50% efficiency improvement, reaching a power conversion efficiency approaching 10%. This P-i-N structure can also provide an enhanced internal electric field and remarkably stable morphology Sequential deposition under harsh thermal stress. We have further demonstrated generality of the P-i-N structure in several other all-polymer systems. Considering the adjustable polymer molecular weight and solubility, the P-i-N device structure can be more beneficial for all-polymer systems. With the design of more crystalline polymers, the antiquated P-i-N structure can further show its strength in all-polymer systems by simplified morphology control and improved carrier extraction, becoming a more favorite device structure than the dominant BHJ structure.
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| 4. |
- Yuan, Jianyu, et al.
(författare)
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Comparing the device physics, dynamics and morphology of polymer solar cells employing conventional PCBM and non-fullerene polymer acceptor N2200
- 2017
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Ingår i: Nano Energy. - : ELSEVIER SCIENCE BV. - 2211-2855 .- 2211-3282. ; 35, s. 251-262
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Tidskriftsartikel (refereegranskat)abstract
- Current all polymer solar cells still suffer from low fill factors (FF) and short-circuit current density (J(sc)) compared with the conventional polymer/fullerene system. Herein in this work, devices using PTP8 as the electron donor and [70]PCBM as well as widely used polymer N2200 as the electron acceptor were systematically studied and compared. The major loss mechanisms in the all polymer solar cells were investigated to understand their relatively lower performance than the PTP8/fullerene system. By performing in-depth analysis on ultrafast transient transmission spectroscopy results, we estimated that in PTP8/N2200 device nearly half of the charges recombine geminately, which is confirmed as the major factor hindering the device performance of all polymer solar cells compared with polymer/fullerene system. Through thorough morphology analysis, the low charge generation efficiency is attributed to the reduced crystallinity of N2200 in the blend film and the unfavorable face-to-edge orientation at the donor/acceptor heterojunction. Coupling these results with knowledge from efficient polymer/fullerene systems, the future design of new polymers can devote to increase the attraction between the pi face of donor and acceptor, leading to enhanced face-to-face orientation at the heterojunction, while maintaining a high pi-pi stacking order for each polymer.
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