The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets

Classen, Andrej; Chochos, Christos L.; Lüer, Larry; Gregoriou, Vasilis G.; Wortmann, Jonas; Osvet, Andres; Forberich, Karen; McCulloch, Iain; Heumüller, Thomas; Brabec, Christoph J.

doi:10.1038/s41560-020-00684-7

Cited by 267 publications

(349 citation statements)

References 36 publications

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“…[146] However, many reports indicate that NFA OSCs with small S 1 -CT energetic offsets can exhibit ΔV nr values that are significantly lower than those of large offset systems for the same E CT . [9,108,126,148] Such observations were first reported by Liu et al, who proposed a correlation between nonradiative recombination losses and the S 1 -CT energetic offset (Figure 16a). [115] Subsequently, other recent works have also shown that reduced S 1 -CT offsets and relatively emissive S 1 states lead to reduced nonradiative recombination losses.…”

Section: Voltage Lossessupporting

confidence: 74%

“…For example, Classen et al have qualitatively described the charge generation processes in low-offset NFA OSCs using a Boltzmann-type equilibrium between local exciton and charge transfer states. [126] Using this model, they proposed that when the HOMO offset between the donor material and the NFA becomes too small (<100 meV), the equilibrium will favor the presence of local exciton states over CT states. Consequently, the majority of photogenerated states will decay via the NFA singlet exciton, instead of progressing into free charge carriers via the CT state manifold.…”

Section: Charge Generationmentioning

confidence: 99%

“…Additionally, there is growing evidence that a small S 1 -1 CT offset can enable efficient thermal re-excitation from 1 CT back to S 1 , [9,115] resulting in an equilibrium between S 1 , CT, and FC in OSC devices [132,151] Indeed, in their recent study, Classen et al claim that the S 1 -1 CT offset is the primary factor determining ΔV nr in OSCs, irrespective of any S 1 -1 CT hybridization that may be present. [126] Here, they synthesized a series of four structurally related donor polymers with a gradually decreasing HOMO energy. By pairing these polymers with a selection of NFAs and PC 70 BM (chemical structures shown in Figure 2), the HOMO-HOMO offset could be systematically controlled.…”

Section: Wwwadvancedsciencenewscommentioning

confidence: 99%

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Section: Voltage Lossessupporting

confidence: 74%

Section: Charge Generationmentioning

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“…It is important to mention that the absence of CT states as well as long singlet exciton lifetimes is not impossible for FAs. An exciton lifetime on the order of 1 ns was measured for PCBM thin films, [ 28 ] which is comparable to the one of the high efficiency NFA Y6 [ 27 ] and hybridized interface states were reported as well for fullerene–polymer blends. [ 29 ] A prerequisite to both is the sufficient alignment of the donor´s and acceptor´s HOMO levels.…”

Section: Opv Progressmentioning

confidence: 72%

“…As charge generation is slowing down for well‐matched energy levels, the singlet exciton lifetime starts to determine the external quantum efficiency (EQE). [ 27 ] An unprecedented large single exciton lifetime was reported for selected NFA systems, which enabled to reduce non‐radiative Voc losses to a minimum while still maintaining high EQE values. It is important to mention that the absence of CT states as well as long singlet exciton lifetimes is not impossible for FAs.…”

Section: Opv Progressmentioning

confidence: 99%

Material Strategies to Accelerate OPV Technology Toward a GW Technology

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the worldwide peak capacity of solar energy production has caught up with wind power, and is expected to be the first renewable energy to exceed the TWp limit in the next few years, probably already by 2023. [1] Solar Power Europe reports levelized cost of electricity (LCOE) for photovoltaic power to range from 5 c (kWh) −1 in the North of Europe like in Helsinki and 3 c (kWh) −1 in the south of Europe, like in Malaga, which will further go down to 3 c (kWh) −1 respectively 1c (kWh) −1. [2] Fraunhofer ISE reports in the 2019 PV report that photovoltaic installations are dominated by crystalline silicon (c-Si) with a market share of over 95% in solar farms and on rooftops. [3] With the rise of the solar power century, photovoltaic applications and installations will go beyond the traditional green field power plants and enter every aspect of our daily life. Urban, naval and space mobility, residential buildings and business towers, all types of facades, portable and Internet of Things (IoT) applications, clothing-almost any aspect of our life can and will be powered by solar energy. While c-Si appears untouchable as leading PV main stream technology for a longer time, many of the new applications which rely on flexibility, transparency, color management, integrability or simply elegant appearance require novel photovoltaic materials and technologies.

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A Difluoro‐Monobromo End Group Enables High‐Performance Polymer Acceptor and Efficient All‐Polymer Solar Cells Processable with Green Solvent under Ambient Condition

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In this paper, a difluoro-monobromo end group is designed and synthesized, which is then used to construct a novel polymer acceptor (named PY2F-T) yielding high-performance all-polymer solar cells with 15.22% efficiency. The fluorination strategy can increase the intramolecular charge transfer and interchain packing of the previous PY-T based acceptor, and significantly improve photon harvesting and charge mobility of the resulting polymer acceptor. In addition, detailed morphology investigations reveal that the PY2F-T-based blend shows smaller domain spacing and higher domain purity, which significantly suppress charge recombination as supported by time-resolved techniques. These polymer properties enable simultaneously enhanced J SC and FF of the PY2F-T-based devices, eventually delivering device efficiencies of over 15%, significantly outperforming that of the devices based on the non-fluorinated PY-T polymer (13%). More importantly, the PY2F-T-based active layers can be processed under ambient conditions and still achieve a 14.37% efficiency. They can also be processed using non-halogenated solvent o-xylene (no additive) and yield a decent performance of 13.05%. This work demonstrates the success of the fluorination strategy in the design of high-performance polymer acceptors, which provide guidelines for developing new all-PSCs with better efficiencies and stabilities for commercial applications.

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The role of exciton lifetime for charge generation in organic solar cells at negligible energy-level offsets

Cited by 267 publications

References 36 publications

The Path to 20% Power Conversion Efficiencies in Nonfullerene Acceptor Organic Solar Cells

The Path to 20% Power Conversion Efficiencies in Nonfullerene Acceptor Organic Solar Cells

Material Strategies to Accelerate OPV Technology Toward a GW Technology

A Difluoro‐Monobromo End Group Enables High‐Performance Polymer Acceptor and Efficient All‐Polymer Solar Cells Processable with Green Solvent under Ambient Condition

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