Suppressing the Surface Recombination and Tuning the Open-Circuit Voltage of Polymer/Fullerene Solar Cells by Implementing an Aggregative Ternary Compound

Galli, Diana; Gasparini, Nicola; Förster, Michael; Eckert, A.; Widling, Christian; Killian, Manuela S.; Avgeropoulos, Apostolos; Gregoriou, Vasilis G.; Scherf, Ullrich; Chochos, Christos L.; Brabec, Christoph J.; Ameri, Tayebeh

doi:10.1021/acsami.8b09174

Cited by 17 publications

(18 citation statements)

References 57 publications

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“…And the blend miscibility was calculated using the Flory–Huggins interaction parameters (χ). [ 21,37 ] As shown in Tables S13 and S14, Supporting Information, we observed that with the increment of M w and the reduction of PDI, the surface energy values ( γ s ) of PM6 gradually diminish, leading to the increase of χ values. In general, with the rise of the χ values, the miscibility of the two compounds decreases, leading to more pronounced phase separation and higher domain purity, and vice versa.…”

Section: Resultsmentioning

confidence: 87%

The Intrinsic Role of Molecular Mass and Polydispersity Index in High‐Performance Non‐Fullerene Polymer Solar Cells

Shi

Wang

et al. 2020

Advanced Energy Materials

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efficiencies (PCEs) rapidly improving from 11% to extend to 17% over the past five years. [9,10,11,12] However, a number of works have shown that non-fullerene PSCs also suffered from rapid performance degradation over time, particularly upon exposure to oxygen, light or elevated temperatures. [13,14,15,16] It can be seen that the development of highly efficient PSCs that show stable photovoltaic performance without adverse degradation remains a significant challenge in this field. [14] Extensive efforts are directed at understanding BHJ morphology degradation resulting from internal factors, [16,17,18,19] synergistic reaction mechanisms, [20,21,22,23] and external stresses. [14] For instance, photooxidation and photostability of active layers are strongly dependent on the sidechain and end-group engineering of the NFAs. [16,24] Increased molecular order and crystallinity have proved to be a benefit for the photostability and thermal stability. [25,26] The high glass transition temperature and proper miscibility of D/A materials can be positively related to the enhanced thermal stability of relevant active layers. [20,27] However, the material structure-device performance correlation is still far from being well understood. Given the greater synthetic complexity of polymer donors compared to the NFAs with relatively well-defined molecular structures, it is interesting to consider whether such PSCs employing polymer donors by fine-tuning their degree of polymerization (including weight-average molecular weight (M w ) and polydispersity (PDI)) can exhibit reduced degradation losses under various external stresses. Recently, a few studies also shed light on the influence of the molecular mass of polymer donors on the underlying degradation mechanisms measured under multiple external stresses. For instance, it has been shown that the composition of the polymer, in terms of M w values, significantly influences the burn-in phase. [28,29,30] In addition, increasing molecular weight but narrowing its distribution can effectively improve the photostability and thermal stability of the fullerene-based PSCs. [29,31] These stability investigations have not only gained a better understanding of the degradation mechanisms associated with the molecular nature but also raised a fundamental question as to whether the degradation behaviors of PSCs is inherent to the conjugated polymers and cannot be overcome. To our knowledge, a subject linking the degradation features to the degree of polymerization has not yet been fully covered in The degree of polymerization can cause significant changes in the blend microstructure and physical mechanism of the active layer of non-fullerene polymer solar cells, resulting in a huge difference in device performance. However, the diversity of stability issues, including photobleaching stability, storage stability, photostability, thermal stability, and mechanical stability, and more, poses a challenge for the degree of polymerization to comprehensively address the trade-off between device efficie...

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Section: Resultsmentioning

confidence: 87%

The Intrinsic Role of Molecular Mass and Polydispersity Index in High‐Performance Non‐Fullerene Polymer Solar Cells

Shi

Wang

et al. 2020

Advanced Energy Materials

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“…113 Alternatively, it has also been suggested that some ternary blends result in a spontaneous segregation of the third component to the surface of the blend resulting in an increased open-circuit voltage and improved charge extraction. 114 The application of our methodology to these ternary material systems will allow the accurate determination of both their energetic and compositional profiles. The ability to cross organic/organic and organic/inorganic interfaces and accurately determine the energetic alignment makes our methodology of great interest to the study of complete photovoltaic devices (including charge extraction layers) as well as tandem organic photovoltaics.…”

Section: Discussionmentioning

confidence: 99%

Visualizing the Vertical Energetic Landscape in Organic Photovoltaics

Lami

Weu

Zhang

et al. 2019

Joule

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Energy level diagrams in organic electronic devices play a crucial role in device performance and interpretation of device physics. In the case of organic solar cells, it has become routine to estimate the photovoltaic gap of the donor:acceptor blend using the energy values measured on the individual blend components, resulting in a poor agreement with the corresponding open-circuit voltage of the device. To address this issue, we developed a method that allows a direct visualisation of the vertical energetic landscape in the blend, obtained by combining ultraviolet photoemission spectroscopy and argon cluster etching. We investigate both model and high-performance photovoltaic systems and demonstrate that the resulting photovoltaic gaps are in close agreement with the measured CT energies and open-circuit voltages. Furthermore, we show that this method allows us to study the evolution of the energetic landscape upon environmental degradation, critically important for understanding degradation mechanisms and development of mitigation strategies.

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“…In this contribution we analyzed temperature and light modulated V oc in a series of nonfullerene BHJ solar cells with conventional or inverted device architecture and a systematically tuned effective bandgap E g,eff in a wide range from 1.0 to 1.62 eV. The temperature‐dependent V oc versus light intensity slopes S of the studied systems with the inverted device structure revealed contributions of different recombination mechanisms, i.e., bimolecular recombination, bulk, and surface trap‐assisted (also called Shockley–Read–Hall, SRH) recombination, [ 25–27 ] in various ratios of the respective net recombination rates. By contrast, recombination losses in the reference system, with the conventional device configuration, could be well described only employing the dominant bimolecular recombination mechanism.…”

Section: Introductionmentioning

confidence: 99%

“…The rapid development of nonfullerene acceptors, which allow a flexible molecular structure design and with that tunable photoelectrical properties [1][2][3][4][5] triggered the recent record efficiencies of organic solar cells. [6][7][8] The bandgap engineering of nonfullerene acceptors promoted the development of narrow and ultranarrow S of the studied systems with the inverted device structure revealed contributions of different recombination mechanisms, i.e., bimolecular recombination, bulk, and surface trap-assisted (also called Shockley-Read-Hall, SRH) recombination, [25][26][27] in various ratios of the respective net recombination rates. By contrast, recombination losses in the reference system, with the conventional device configuration, could be well described only employing the dominant bimolecular recombination mechanism.…”

Section: Introductionmentioning

confidence: 99%

Temperature and Light Modulated Open‐Circuit Voltage in Nonfullerene Organic Solar Cells with Different Effective Bandgaps

Брус

Schopp

et al. 2020

Advanced Energy Materials

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bandgap systems for the emerging fields of organic semitransparent photovoltaics and near-infrared photodiodes. [9,10] So far, there are no systematic studies on the relationship between the effective bandgap E g,eff , defined by the HOMO of the donor and the LUMO of the acceptor, the density of states (DOS) distribution and multimechanism recombination processes in nonfullerene organic solar cells. However, all mentioned parameters both individually and synergistically are known to be strongly influential on photoelectronic processes and, thus, on the power conversion efficiency (PCE). A specific interest represents the temperature and light intensity dependence of the open-circuit voltage V oc that is selectively sensitive to these parameters and remains immune to the parasitic effects of the series resistance and large shunt. [11-13] Temperature is a macroscopic parameter, which appears in exponential functions in all major equations that describe charge carrier concentration, recombination, and transport processes. This prevalence of the temperature in most equations is mainly caused by the reliance on the Fermi-Dirac distribution or thermally activated processes. [13,14] Hence, temperature is an essential parameter to consider for the analysis of electronic processes in all types of semiconductor materials and devices. [13,15] A controllable change of temperature allows the modulation of basic electronic processes both mechanistically and quantitatively in organic bulk-heterojunction (BHJ) solar cells. In contrast to studies across different devices, uncontrollable fabrication-related deviations in morphology and defect concentrations can be excluded as a parameter of influence. However, in OPVs, the temperature effect is rarely studied and if so, only to inspect the temperature-dependent trends for the main photoelectric parameters (open circuit voltage (V oc), short circuit current density (J sc), fill factor (FF)) and PCE of organic BHJ solar cells. [16-21] Even less attention has been paid to the investigation of temperature-dependent generationrecombination processes in BHJ layers and, specifically, at their interfaces with electrical contacts. [22-24] In this contribution we analyzed temperature and light modulated V oc in a series of nonfullerene BHJ solar cells with conventional or inverted device architecture and a systematically tuned effective bandgap E g,eff in a wide range from 1.0 to 1.62 eV. The temperature-dependent V oc versus light intensity slopes The relationship of the temperature-light intensity dependence of opencircuit voltage V oc in nonfullerene-based organic solar cells with their material characteristics and multimechanism recombination parameters is described. The systematic variation of the effective bandgap E g,eff and the electrode layers allows the observation of different relative contributions of bimolecular, bulk, and surface trap-assisted recombination mechanisms. The complementary advantages of the analytical model and the established voltage-impedance spectroscopy techn...

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Suppressing the Surface Recombination and Tuning the Open-Circuit Voltage of Polymer/Fullerene Solar Cells by Implementing an Aggregative Ternary Compound

Cited by 17 publications

References 57 publications

The Intrinsic Role of Molecular Mass and Polydispersity Index in High‐Performance Non‐Fullerene Polymer Solar Cells

The Intrinsic Role of Molecular Mass and Polydispersity Index in High‐Performance Non‐Fullerene Polymer Solar Cells

Visualizing the Vertical Energetic Landscape in Organic Photovoltaics

Temperature and Light Modulated Open‐Circuit Voltage in Nonfullerene Organic Solar Cells with Different Effective Bandgaps

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