| 1. |
- Kan, Zhipeng, et al.
(författare)
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Charge transport control via polymer polymorph modulation in ternary organic photovoltaic composites
- 2016
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Ingår i: Journal of Materials Chemistry A. - : Royal Society of Chemistry (RSC). - 2050-7488 .- 2050-7496. ; 4:4, s. 1195-1201
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Tidskriftsartikel (refereegranskat)abstract
- The control on the charge transport properties of ternary organic photovoltaic P3HT : PCBM : QBT devices is enabled by modulating the distribution of P3HT polymorphs in the device photoactive layers. Negligible amounts of QBT induce striking modifications in the P3HT lamellar stacking direction, forming both densely packed and non-densely packed P3HT chains. The former reduce the charge carrier recombination rate, enabling an increased fill factor and short-circuit device photocurrent.
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| 2. |
- Karuthedath, Safakath, et al.
(författare)
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Buildup of Triplet-State Population in Operating TQ1:PC71BM Devices Does Not Limit Their Performance
- 2020
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Ingår i: The Journal of Physical Chemistry Letters. - : AMER CHEMICAL SOC. - 1948-7185. ; 11:8, s. 2838-2845
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Tidskriftsartikel (refereegranskat)abstract
- Triplet generation in organic solar cells has been considered a major loss channel. Determining the density of the triplet-state population in an operating device is challenging. Here, we employ transient absorption (TA) spectroscopy on the quinoxaline-thiophene copolymer TQ1 blended with PC71BM, quantify the transient charge and tripletstate densities, and parametrize their generation and recombination dynamics. The charge recombination parameters reproduce the experimentally measured current-voltage characteristics in charge carrier drift-diffusion simulations, and they yield the steady-state charge densities. We demonstrate that triplets are formed by both geminate and nongeminate recombination of charge carriers and decay primarily by triplet-triplet annihilation. Using the charge densities in the rate equations describing triplet-state dynamics, we find that triplet-state densities in devices are in the range of charge carrier densities. Despite this substantial triplet-state buildup, TQ1:PC71BM devices exhibit only moderate geminate recombination and significantly reduced nongeminate charge recombination, with reduction factors between 10(-4) and 10(-3) compared to Langevin recombination.
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| 3. |
- Karuthedath, Safakath, et al.
(författare)
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Thermal annealing reduces geminate recombination in TQ1:N2200 all-polymer solar cells
- 2018
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Ingår i: Journal of Materials Chemistry A. - : ROYAL SOC CHEMISTRY. - 2050-7488 .- 2050-7496. ; 6:17, s. 7428-7438
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Tidskriftsartikel (refereegranskat)abstract
- combination of steady-state and time-resolved spectroscopic measurements is used to investigate the photophysics of the all-polymer bulk heterojunction system TQ1:N2200. Upon thermal annealing a doubling of the external quantum efficiency and an improved fill factor (FF) is observed, resulting in an increase in the power conversion efficiency. Carrier extraction is similar for both blends, as demonstrated by time-resolved electric-field-induced second harmonic generation experiments in conjunction with transient photocurrent studies, spanning the ps-mu s time range. Complementary transient absorption spectroscopy measurements reveal that the different quantum efficiencies originate from differences in charge carrier separation and recombination at the polymer-polymer interface: in as-spun samples similar to 35% of the charges are bound in interfacial charge-transfer states and recombine geminately, while this pool is reduced to similar to 7% in thermally-annealed samples, resulting in higher short-circuit currents. Time-delayed collection field experiments demonstrate a field-dependent charge generation process in as-spun samples, which reduces the FF. In contrast, field-dependence of charge generation is weak in annealed films. While both devices exhibit significant non-geminate recombination competing with charge extraction, causing low FFs, our results demonstrate that the donor/acceptor interface in all-polymer solar cells can be favourably altered to enhance charge separation, without compromising charge transport and extraction.
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| 4. |
- Sun, Huiliang, et al.
(författare)
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A Narrow-Bandgap n-Type Polymer with an Acceptor-Acceptor Backbone Enabling Efficient All-Polymer Solar Cells
- 2020
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Ingår i: Advanced Materials. - : WILEY-V C H VERLAG GMBH. - 0935-9648 .- 1521-4095. ; 32
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Tidskriftsartikel (refereegranskat)abstract
- Narrow-bandgap polymer semiconductors are essential for advancing the development of organic solar cells. Here, a new narrow-bandgap polymer acceptor L14, featuring an acceptor-acceptor (A-A) type backbone, is synthesized by copolymerizing a dibrominated fused-ring electron acceptor (FREA) with distannylated bithiophene imide. Combining the advantages of both the FREA and the A-A polymer, L14 not only shows a narrow bandgap and high absorption coefficient, but also low-lying frontier molecular orbital (FMO) levels. Such FMO levels yield improved electron transfer character, but unexpectedly, without sacrificing open-circuit voltage (V-oc), which is attributed to a small nonradiative recombination loss (E-loss,E-nr) of 0.22 eV. Benefiting from the improved photocurrent along with the high fill factor andV(oc), an excellent efficiency of 14.3% is achieved, which is among the highest values for all-polymer solar cells (all-PSCs). The results demonstrate the superiority of narrow-bandgap A-A type polymers for improving all-PSC performance and pave a way toward developing high-performance polymer acceptors for all-PSCs.
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