Thermal annealing reduces geminate recombination in TQ1:N2200 all-polymer solar cells

Karuthedath, Safakath; Melianas, Armantas; Kan, Zhipeng; Pranculis, Vytenis; Wohlfahrt, Markus; Khan, Jafar Iqbal; Gorenflot, Julien; Xia, Yuxin; Inganäs, Olle; Gulbinas, Vidmantas; Kemerink, Martijn; Laquai, Frédéric

doi:10.1039/c8ta01692e

Cited by 50 publications

(66 citation statements)

References 46 publications

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“…For the purpose of J-V simulation, we first measured the optical constants, namely, refractive index and extinction coefficient, of all active layers using ellipsometry ( Figure S3, Supporting Information). [36] Figure 2b shows that the simulated J-V curves (solid lines) closely resemble the experimentally measured J-V data (symbols). Rate constant values of ≈1 × 10 −12 cm 3 s −1 for PBDT(T)[2F]T-based cells, and ≈7 × 10 −12 cm 3 s −1 for PBDB-T-based device, were found to yield best fits between experiment and simulation.…”

Section: Resultssupporting

confidence: 56%

Key Parameters Requirements for Non‐Fullerene‐Based Organic Solar Cells with Power Conversion Efficiency >20%

et al. 2019

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The reported power conversion efficiencies (PCEs) of nonfullerene acceptor (NFA) based organic photovoltaics (OPVs) now exceed 14% and 17% for single‐junction and two‐terminal tandem cells, respectively. However, increasing the PCE further requires an improved understanding of the factors limiting the device efficiency. Here, the efficiency limits of single‐junction and two‐terminal tandem NFA‐based OPV cells are examined with the aid of a numerical device simulator that takes into account the optical properties of the active material(s), charge recombination effects, and the hole and electron mobilities in the active layer of the device. The simulations reveal that single‐junction NFA OPVs can potentially reach PCE values in excess of 18% with mobility values readily achievable in existing material systems. Furthermore, it is found that balanced electron and hole mobilities of >10 −3 cm 2 V −1 s −1 in combination with low nongeminate recombination rate constants of 10 −12 cm 3 s −1 could lead to PCE values in excess of 20% and 25% for single‐junction and two‐terminal tandem OPV cells, respectively. This analysis provides the first tangible description of the practical performance targets and useful design rules for single‐junction and tandem OPVs based on NFA materials, emphasizing the need for developing new material systems that combine these desired characteristics.

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Section: Resultssupporting

confidence: 56%

Key Parameters Requirements for Non‐Fullerene‐Based Organic Solar Cells with Power Conversion Efficiency >20%

et al. 2019

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“…We have studied more materials with these combinations of transient spectroscopy and KMC, and found similar physics to rule in polymer/polymer blends [182] and in evaporated molecule/molecule blends. We have studied more materials with these combinations of transient spectroscopy and KMC, and found similar physics to rule in polymer/polymer blends [182] and in evaporated molecule/molecule blends.…”

Section: Wwwadvmatde Wwwadvancedsciencenewscommentioning

confidence: 73%

“…It has moved rapidly, with a PCE of 3.3% in 2013, [238] 5.7% in 2014, [239] at 7.7% in 2015, [240,241] at 8% in 2016, [242] and 10% in 2017. [182] Clearly, the morphology of the blends influences photocurrent and fill factor. We found that thermal annealing of the spincoated blend can lead to improvement of the PCE by almost 2 times, to reach 4.4% PCE.…”

Section: Polymer/polymer Blendsmentioning

confidence: 99%

Organic Photovoltaics over Three Decades

2018

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The development of organic semiconductors for photovoltaic devices, over the last three decades, has led to unexpected performance for an alternative choice of materials to convert sunlight to electricity. New materials and developed concepts have improved the photovoltage in organic photovoltaic devices, where records are now found above 13% power conversion efficiency in sunlight. The author has stayed with the topic of organic materials for energy conversion and energy storage during these three decades, and makes use of the Hall of Fame now built by Advanced Materials, to present his view of the path travelled over this time, including motivations, personalities, and ambitions.

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“…[15] This was attributed to dead ends where carriers need to hop against the direction of the field to escape the spatial trap and continue drift. [17] We tentatively associate spatial traps with chain ends that hamper the initial, short-range separation of the photocreated electron-hole pair, leading to strongly enhanced geminate recombination. Upon annealing the effect of these spatial traps largely vanishes.…”

Section: Introductionmentioning

confidence: 86%

“…In a broader perspective, these results highlight a morphological problem which may occur in all bulk-heterojunction OPVs, and show that relatively simple processing steps, such as thermal annealing, can possibly at least partly resolve the issue. [17] Figure 2a shows the dependence of the TDCF photocurrent kinetics on the collection delay time measured at close to zero effective generation voltage. Note that all voltages specified here and below are effective values that account for the applied voltage and the built-in potential U eff = U appl + V BI (V Bl = −0.47 V).…”

Section: Introductionmentioning

confidence: 99%

Dead Ends Limit Charge Carrier Extraction from All‐Polymer Bulk Heterojunction Solar Cells

Jasiu̅nas

Melianas

Xia

et al. 2018

Adv Elect Materials

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accepting material in one phase and electron donating material in the other. [2] However, such strongly phase-separated morphologies are prone to cause extraction problems due to the formation of dead ends and/or isolated domains. [3] Fortunately, in state-of-the-art polymer:fullerene and polymer:small molecule organic photovoltaic (OPV) devices performance is not limited by recombination losses during extraction (but mostly by voltage losses) as witnessed by large fill factors and relatively high internal quantum efficiency (IQE) values. [4] As a consequence, extraction of photocreated charge carriers can often be well described using models that consider the BHJ as an effective medium with the energy levels of the medium reflecting the highest occupied molecular orbital (HOMO) of the donor and the lowest unoccupied molecular orbital (LUMO) of the acceptor. [5,6] In such models, morphological effects are only implicitly accounted for by the values of the (effective) transport and disorder parameters. One may wonder why this evident simplification works so well. It has recently become clear that one important reason might be that charge carriers in organic semiconductors may actually be able to move over relatively large distances, up to several nm, by longrange tunneling or molecular superexchange. [7][8][9][10] This enables transport to non-nearest neighbor sites, and thereby greatly relaxes the need to have connected phases of pure material for efficient charge transport.OPV devices using non-fullerene acceptors are currently receiving increased attention and start to outperform fullerenebased devices. [11][12][13] While having evident benefits over fullerenes in terms of improved absorption and larger energy level tunability, charge transport and extraction in non-fullerene BHJ is still less understood. In particular all-polymer BHJ, in which both donor and acceptor materials are polymers, are in many respects in their infancy. While the entanglement of polymer chains in such BHJ is expected to lead to a much needed increased morphological stability at elevated temperatures inherent to solar cell operation, [14] the same entanglement can also lead to extraction problems. Such problems are less pronounced in BHJ where at least one of the constituents is a small molecule and dispersion of a minor fraction of the small molecule in the other compound is sufficient to enable reasonably efficient charge transport between these molecules. [7,9] However, the required "molecular" dispersion, in which sites of Extraction of photocreated charge carriers from a prototypical all-polymer organic solar cell is investigated by combining transient photocurrent and time-delayed collection field experiments with numerical simulations. It is found that extraction is significantly hampered by charges getting trapped in spatial traps that are tentatively attributed to dead ends in the intermixed polymer network-in photovoltaic devices based on the same donor polymer and a fullerene acceptor this effect is much weaker. The slow-dow...

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Thermal annealing reduces geminate recombination in TQ1:N2200 all-polymer solar cells

Abstract: Annealing of TQ1:N2200 photovoltaic blends reduces geminate charge recombination, without compromising charge extraction, leading to higher photocurrents and device efficiency.

Cited by 50 publications

References 46 publications

Key Parameters Requirements for Non‐Fullerene‐Based Organic Solar Cells with Power Conversion Efficiency >20%

Key Parameters Requirements for Non‐Fullerene‐Based Organic Solar Cells with Power Conversion Efficiency >20%

Organic Photovoltaics over Three Decades

Dead Ends Limit Charge Carrier Extraction from All‐Polymer Bulk Heterojunction Solar Cells

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