Assessing the Photovoltaic Quality of Vacuum‐Thermal Evaporated Organic Semiconductor Blends

Kaienburg, Pascal; Jungbluth, Anna; Habib, Irfan; Kesava, Sameer Vajjala; Nyman, Mathias; Riede, Moritz

doi:10.1002/adma.202107584

Cited by 7 publications

(7 citation statements)

References 59 publications

(144 reference statements)

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“…Note that since photocurrent generation in our bilayer devices is limited, V oc losses of tens of millivolts resulting from J sc losses , (Δ V oc sc ) are considerable. C 60 /ZnPc shows large nonradiative and radiative voltage losses of 520 and 390 mV, respectively, with the latter being reduced to 160 mV for C 60 /F 4 ZnPc, matching our reported behavior of corresponding BHJs . The radiative voltage loss drops significantly for Y6/ZnPc to 30 mV, which is lower than any of the VTE systems we have investigated previously …”

Section: Resultssupporting

confidence: 88%

“…A detailed investigation of the origins of this behavior and calculations of the molecular energy levels is beyond the scope of this work. We note that we previously demonstrated high nonradiative losses of F x ZnPc:C 60 blends compared to other SM VTE donors and that even lower nonradiative losses have been demonstrated for similar bilayer devices with DTDCTB as an evaporated donor (see also Figure S2). To conclude, reduced nonradiative voltage losses that do not follow the energy gap law, likely due to CT-S1 hybridization, , are a further beneficial feature of polymer/NFA blends that may translate to NFA/VTE-SM systems.…”

Section: Resultssupporting

confidence: 50%

“…C 60 /ZnPc shows large nonradiative and radiative voltage losses of 520 and 390 mV, respectively, with the latter being reduced to 160 mV for C 60 /F 4 ZnPc, matching our reported behavior of corresponding BHJs. 36 The radiative voltage loss drops significantly for Y6/ZnPc to 30 mV, which is lower than any of the VTE systems we have investigated previously. 36 The nonradiative loss in Y6/F 4 ZnPc of 280 mV is ∼200 mV smaller than that in C 60 /F 4 ZnPc, even though V oc,rad is 100 mV lower in Y6/F 4 ZnPc.…”

Section: ■ Resultsmentioning

confidence: 62%

“…36 The radiative voltage loss drops significantly for Y6/ZnPc to 30 mV, which is lower than any of the VTE systems we have investigated previously. 36 The nonradiative loss in Y6/F 4 ZnPc of 280 mV is ∼200 mV smaller than that in C 60 /F 4 ZnPc, even though V oc,rad is 100 mV lower in Y6/F 4 ZnPc. This trend contradicts the energy gap law, which predicts higher nonradiative loss for lower V oc,rad .…”

Section: ■ Resultsmentioning

confidence: 62%

“…The J sc of our C 60 /F 4 ZnPc and C 60 /ZnPc devices is 3.9 mA/ cm 2 in both cases as expected from essentially identical absorption spectra and previous literature. 35,36 However, Y6/ F 4 ZnPc shows a decreased J sc of 1.9 mA/cm 2 compared to the Y6/ZnPc (4 mA/cm 2 ) despite no change in absorption spectra indicated by the similar shape of the EQE spectra. This indicates a drop in exciton splitting efficiency for the fluorinated donor, which is well known for systems where energetic offsets are insufficient.…”

Section: ■ Resultsmentioning

confidence: 90%

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Vacuum-Deposited Donors for Low-Voltage-Loss Nonfullerene Organic Solar Cells

Kaienburg

Bristow

Jungbluth

et al. 2023

ACS Appl. Mater. Interfaces

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The advent of nonfullerene acceptors (NFAs) enabled records of organic photovoltaics (OPVs) exceeding 19% power conversion efficiency in the laboratory. However, high-efficiency NFAs have so far only been realized in solution-processed blends. Due to its proven track record in upscaled industrial production, vacuum thermal evaporation (VTE) is of prime interest for real-world OPV commercialization. Here, we combine the benchmark solution-processed NFA Y6 with three different evaporated donors in a bilayer (planar heterojunction) architecture. We find that voltage losses decrease by hundreds of millivolts when VTE donors are paired with the NFA instead of the fullerene C60, the current standard acceptor in VTE OPVs. By showing that evaporated small-molecule donors behave much like solution-processed donor polymers in terms of voltage loss when combined with NFAs, we highlight the immense potential for evaporable NFAs and the urgent need to direct synthesis efforts toward making smaller, evaporable compounds.

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Section: Resultssupporting

confidence: 88%

Section: Resultssupporting

confidence: 50%

Section: ■ Resultsmentioning

confidence: 62%

Section: ■ Resultsmentioning

confidence: 62%

Section: ■ Resultsmentioning

confidence: 90%

See 3 more Smart Citations

Vacuum-Deposited Donors for Low-Voltage-Loss Nonfullerene Organic Solar Cells

Kaienburg

Bristow

Jungbluth

et al. 2023

ACS Appl. Mater. Interfaces

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Increasing the Ionization Energy Offset to Increase the Quantum Efficiency in Non‐Fullerene Acceptor‐Based Organic Solar Cells: How Far Can We Go?

Gorenflot

Alsufyani

Alqurashi

et al. 2023

Adv Materials Inter

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more than 30 years of empirical optimization [1,2] from the first proof of concept by Tang delivering only 1% power conversion efficiency (PCE) in 1986, [3] to develop the latest Y-series of non-fullerene acceptor (NFA) molecules [4,5] that now yield efficiencies close to 20%. [6][7][8][9][10][11] The field of OPV has always been in need of design principles that could guide the synthesis of new molecules. In parallel to molecular engineering, our understanding of the photophysics governing the solar cell performances has considerably increased in the last 30 years, and such sets of meaningful design rules have started to solidify. [12][13][14][15] Furthermore, first principlebased computational materials chemistry has progressed to the point where energy levels can not only be computed in the gas phase, but also extrapolated to films, which allows for screening many potential structures of OPV materials and selecting the most promising for synthesis. [14] For low-bandgap NFA-based solar cells, we previously showed that the acceptor's ionization energy has to be ≈0.45 eV higher (more negative with respect to vacuum) than that of the donor, to maximize exciton quenching by hole transfer from the acceptor to the donor and in turn the solar cells' internal quantum efficiency (IQE). [12,14] We showed that this hole transfer efficiency sets a ceiling to the solar cells' IQE. The 0.45 eV ionization energy offset ΔIE was shown to be required to counterbalance energy level bending (measured as bias potential B) at the donor-acceptor (D/A) interface, which increases the energy of the interfacial charge transfer (CT) and thus impedes the exciton-to-CT-state transition if ΔIE is low. [12,14,16] The interfacial energy level bending is a consequence of the energetic landscape in NFA-based blends, more specifically the interaction of charges with the surrounding molecules' (NFA and donors) intrinsic quadrupole moments. [12,14,15,17,18] On the other hand, the bending facilitates charge separation (CT to free charge conversion) and diffusion from the interface, explaining the observation of barrier-less charge generation in the top-performing OPV systems. [19] Very recently, we reported that the same applies to ternary blends, composed of one donor and two acceptors. [20] Interestingly, the IQE follows the average IE of both acceptors weighted by their blending (weight) ratio. [20] While Molecular engineering of organic semiconductors provides a virtually unlimited number of possible structures, yet only a handful of combinations lead to state-of-the-art efficiencies in photovoltaic applications. Thus, design rules that guide material development are needed. One such design principle is that in a bulk heterojunction consisting of an electron donor and lower bandgap acceptor an offset (ΔIE) of at least 0.45 eV is required between both materials ionization energies to overcome energy level bending at the donor-acceptor interface, in turn maximizing the charge separation yield and the cell's internal quantum efficiency. The present...

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Effect of Alkyl Side Chains in BDT and 2D‐BDT Small‐Molecules as Donor Materials for Vacuum‐Processed Organic Photovoltaic Devices

Antoine,

Vilches,

Preuss

et al. 2024

Energy Tech

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Nine molecules based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT) and 2D‐BDT derivatives are studied as donor materials in organic photovoltaic (OPV) devices fabricated by thermal evaporation, aiming to understand how different alkyl lateral substituents affect the molecular packing, the charge transport, and, subsequently, the device performance. Synthesis of the molecules is followed by a comprehensive characterization using thermal and differential scanning calorimetry analyses, which confirm their thermal stability and suitability for vacuum‐processed OPV devices. Thermal analysis also demonstrates a strong correlation between the melting point reduction of the molecules and the disorder caused by the alkyl chains. As the synthesized molecules present similar optical properties, the differences in the device performance are caused by the different substituents. BDT derivatives with low melting point temperatures produce reduced current density, hole mobility, and overall device performance, which are attributed to poor molecular packing. Additionally, energy‐dispersive X‐ray spectroscopy analysis suggests phase separation with fullerene, further impacting the efficiency of the devices. The findings indicate that the photovoltaic performance of BDT‐based molecules can be modulated by avoiding aliphatic substituents, providing a strategy for the design of more efficient materials, with thermal evaporation as an ideal method to evaluate and decouple molecular packing from solubility.

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Assessing the Photovoltaic Quality of Vacuum‐Thermal Evaporated Organic Semiconductor Blends

Cited by 7 publications

References 59 publications

Vacuum-Deposited Donors for Low-Voltage-Loss Nonfullerene Organic Solar Cells

Vacuum-Deposited Donors for Low-Voltage-Loss Nonfullerene Organic Solar Cells

Increasing the Ionization Energy Offset to Increase the Quantum Efficiency in Non‐Fullerene Acceptor‐Based Organic Solar Cells: How Far Can We Go?

Effect of Alkyl Side Chains in BDT and 2D‐BDT Small‐Molecules as Donor Materials for Vacuum‐Processed Organic Photovoltaic Devices

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