A unified description of non-radiative voltage losses in organic solar cells

Chen, Xiankai; Qian, Deping; Wang, Yuming; Kirchartz, Thomas; Tress, Wolfgang; Yao, Huifeng; Yuan, Jun; Hülsbeck, Markus; Zhang, Maojie; Zou, Yingping; Sun, Yanming; Li, Yongfang; Hou, Jianhui; Inganäs, Olle; Coropceanu, Veaceslav; Brédas, Jean‐Luc; Gao, Feng

doi:10.1038/s41560-021-00843-4

Cited by 320 publications

(390 citation statements)

References 48 publications

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“…Since V rad oc and V oc are both robust quantities that can be determined accurately, the same holds true for ∆V nr oc . Non-radiative losses are on the order of 200-500 mV in OSCs [25], with some efficient NFA-based blends achieving losses as low as 150 mV [72]. The exact mechanisms of non-radiative recombination in OSCs are still under discussion but non-radiative recombination is generally understood to involve recombination from the CT state via high-energy phonons of about 150 meV [24,73].…”

Section: Db Picture Of V Oc Lossesmentioning

confidence: 99%

Charge transfer state characterization and voltage losses of organic solar cells

2022

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A correct determination of voltage losses is crucial for the development of organic solar cells with improved performance. This requires an in-depth understanding of the properties of interfacial charge transfer (CT) states, which not only set the upper limit for the open-circuit voltage of a system, but also govern radiative and non-radiative recombination processes. Over the last decade, different approaches have emerged to classify voltage losses in organic solar cells that rely on a generic detailed balance approach or additionally include CT state parameters that are specific to organic solar cells. In the latter case, a correct determination of CT state properties is paramount. In this work, we summarize the different frameworks used today to calculate voltage losses and provide an in-depth discussion of the currently most important models used to characterize CT state properties from absorption and emission data of organic thin films and solar cells. We also address practical concerns during the data recording, analysis, and fitting process. Departing from the classical two-state Marcus theory approach, we discuss the importance of quantized molecular vibrations and energetic hybridization effects in organic donor-acceptor systems with the goal to providing the reader with a detailed understanding of when each model is most appropriate.

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Section: Db Picture Of V Oc Lossesmentioning

confidence: 99%

Charge transfer state characterization and voltage losses of organic solar cells

2022

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“…Organic molecular blends based on fullerene acceptors (FAs), have been in the focus of intensive research efforts in the organic solar cell community, due to their reliable performance in the solar energy conversion [1,2]. Despite the recent advent of non-fullerene acceptor systems [3,4] with power conversion efficiencies reaching 18% [5], FA-based blends remain important model systems to study key electronic and optoelectronic processes and limiting factors of organic photovoltaic devices [6][7][8][9][10][11][12].…”

Section: Introductionmentioning

confidence: 99%

Ultrafast carrier dynamics at organic donor–acceptor interfaces—a quantum-based assessment of the hopping model

et al. 2022

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We investigate the charge transfer dynamics of photogenerated excitons at the donor-acceptor interface of an organic solar cell blend under the influence of molecular vibrations. This is examined using an effective Hamiltonian, parametrized by density functional theory calculations, to describe the full quantum behaviour of the relevant molecular orbitals, which are electronically coupled with each other and coupled to over one hundred vibrations (via Holstein coupling). This electron-phonon system is treated in a numerically quasi-exact fashion using the matrix-product-state ansatz. We provide insight into different mechanisms of charge separation and their relation to the electronic driving energy for the separation process. We find ultrafast electron transfer, which for small driving energy is dominated by kinetic processes and at larger driving energies by dissipative phonon emission connected to the prevalent vibration modes. Using this fully quantum mechanical model we perform a benchmark comparison to a recently developed semi-classical hopping approach, which treats the hopping and vibration time scales consistently. We find qualitatively and quantitatively good agreement between the results of the sophisticated matrix-product-state based quantum dynamics and the simple and fast time-consistent-hopping approach.

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“…Straight lines exhibit the maximum Shockley-Queisser efficiencies for the different input LED spectra. Dashed lines incorporate an additional, non-radiative voltage loss of 180 meV representative of the lowest reported values in the literature that are in the range of 0.16-0.2 V. [88,92,93] For the samples, which reached the best efficiencies with the 2700 K LED of Cui et al, the peak around 1.84 eV is overlapping with the position of the Shockley-Queisser maximum, suggesting the band gap to be suitable for this LED illumination. Theoretically, with this kind of LED spectrum a maximum efficiency of 54% is possible, emphasizing the potential for further improvements.…”

Section: Comparing Efficiencies Of Different Publicationsmentioning

confidence: 80%

“…The efficiency improvements in recent generations of organic solar cells have however led to substantially steeper absorption onsets [86,87] and smaller differences between donor, acceptor, and CT state absorption features. [88,89] These developments imply that the original Shockley-Queisser model becomes more relevant with the continuous improvement of OPV efficiencies and motivates our use of the traditional step-function. In addition to the stepfunction absorptance, the detailed balance model also idealizes the contacts (no resistive losses), transport (all photogenerated electron hole pairs are collected), and recombination (only radiative recombination is included in the model).…”

Section: Influence Of Leds With Different Photon Energies On the Performance Of Indoor Solar Cellsmentioning

confidence: 99%

Comparing and Quantifying Indoor Performance of Organic Solar Cells

Lübke

Hartnagel

Angona

et al. 2021

Advanced Energy Materials

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An important application that benefits from the tuneability of band gaps in molecular semiconductors is the use of organic photovoltaics (OPV) for indoor light harvesting. The market of the internet of things (IoT) is emerging remarkably and demands to drive high amounts of off-grid low power consumption devices. [8][9][10][11][12][13] The possibility to produce solution-based, lowcost, and flexible solar foils makes OPV a good candidate to fulfill this demand. Furthermore, the absorption spectra of the active materials can be tuned chemically to match different light sources.Although efficiencies for indoor organic photovoltaics (iOPV) and other emerging indoor photovoltaics (iPV) technologies such as halide perovskites [36][37][38][39][40][41][42][43] or dye-sensitized solar cells [44][45][46][47][48][49][50] have improved substantially, it is hard to quantify progress and determine champion solar cells due to a lack of standardized comparison methods. [12,51,52] Different authors use different conditions to evaluate the performance of their devices. The set-ups differ in the illuminance value (ranging typically from 200 to 1000 lux) and the source of light, namely light emitting diodes (LED) or fluorescent lamps (FL) with varying emission spectra and color temperatures. This makes it difficult to compare devices and regularly leads to the publication of tables or figures where data is compared for different input spectra and illuminances. [43,53,54] The exact spectrum and intensity are, however, more than just a minor inconvenience for data comparison but can have a major impact on the output power at a given illuminance and the efficiency. This is due to several reasons. First, the presence of shunts [55][56][57] can have a substantial effect on the dependence of open-circuit voltage and fill factor on the light intensity under indoor conditions. [55,56,58] Second, the short-circuit current at a given illuminance strongly depends on the overlap of the materials' absorption spectra and the spectral emission power of the light source. [53,59] The exact spectrum is even more critical than for outdoor illumination, because indoor light sources have much more narrow spectra with strong emission between wavelengths of 400 and 700 nm [60,61] as compared to the air mass 1.5 global (AM1.5G) spectrum.In the worst-case scenario, an otherwise well-performing solar cell could exhibit low efficiencies if the color temperature of the light source is not suitable to the specific absorber bandgap. Standardizing indoor spectra as done for outdoor efficiency measurements is not practical given the substantial spectral differences between the used light sources. Furthermore, With increasing efficiencies of non-fullerene acceptor-based organic solar cells, thin-film technology is becoming a promising candidate for indoor light harvesting applications. However, the lack of standardized comparison methods makes it difficult to quantify progress and to compare indoor performance. Herein, a simple method to calculate the efficiency ...

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A unified description of non-radiative voltage losses in organic solar cells

Cited by 320 publications

References 48 publications

Charge transfer state characterization and voltage losses of organic solar cells

Charge transfer state characterization and voltage losses of organic solar cells

Ultrafast carrier dynamics at organic donor–acceptor interfaces—a quantum-based assessment of the hopping model

Comparing and Quantifying Indoor Performance of Organic Solar Cells

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