Film‐Depth‐Dependent Light Reflection Spectroscopy for Photovoltaics and Transistors

Shen, Zichao; Jiang, Yihang; Yu, Jinde; Zhu, Yuanwei; Bu, Laju; Lu, Guanghao

doi:10.1002/admi.202101476

Cited by 9 publications

(6 citation statements)

References 43 publications

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“…As shown in Figure 7b,f, the composition distribution profiles of a-BTR-H4 and Y6 at different film-depths could be fitted by the FLAS plots with the absorption spectra. [59][60][61] Obviously, a-BTR-H4:Y6 with 120 °C TA shows a more uniform phase distribution throughout the whole active layer vertically, especially on the surface of the blend, which is consistent with the above CA and AFM results. The blend film without TA possesses serious vertical phase separation, wherein donor and acceptor both show a gradient distribution with higher concentrations of Y6 near the cathode, and a-BTR-H4 near the anode, respectively.…”

Section: Crystallization Process and Internal State Of Blend Filmssupporting

confidence: 88%

End Group Effect of Asymmetric Benzodithiophene‐Based Donor with Liquid‐Crystal State for Small‐Molecule Binary Solar Cell

Zhao

Huang

Xiao

et al. 2022

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Liquid‐crystal small molecule donor (LC‐SMD) is a new type organic semiconductor, which is attractive not only for the easy synthesis and purification, well‐defined chemical structures, etc., but also for the LC state that makes the crystallinity and aggregation state of molecules adjustable. Here, one new LC‐SMD (a‐BTR‐H4) is synthesized with 1D alkoxyl and 2D thiophene‐alkylthiol side‐chained benzo[1,2‐b:4,5‐b′]dithiophene core, trithiophene π‐bridge, and 3‐(2‐ethylhexyl) rhodanine end group. a‐BTR‐H4 shows low LC transition temperature, 117 °C, however, counterpart material (a‐BTR‐H5) with the same main structure but 3‐ethyl rhodanine terminal group does not show LC properties. Although a‐BTR‐H4/H5 show similar Ultraviolet–visible absorption spectrum and energy levels, a‐BTR‐H4 affords relatively high photovoltaic performances due to favorable blend morphology produced by the consistent annealing temperature of Y6‐based accepters and liquid crystal temperature of donors. Preliminary results indicate that a‐BTR‐H4 gains a power conversion efficiency (PCE) of 11.36% for Y6‐based devices, which is ascribed to better light harvest as well as balanced carrier generation and transport, while a‐BTR‐H5 obtains 7.57% PCE. Therefore, some materials with unique nematic LC phase have great application potential in organic electronics, and further work to utilize a‐BTR‐H4 for high‐performance device is underway.

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Section: Crystallization Process and Internal State Of Blend Filmssupporting

confidence: 88%

End Group Effect of Asymmetric Benzodithiophene‐Based Donor with Liquid‐Crystal State for Small‐Molecule Binary Solar Cell

Zhao

Huang

Xiao

et al. 2022

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“…The correlation between experimental and predicted values illustrates the usefulness of the polariton concept for understanding the optical properties of molecular crystals. , Yet surprisingly little experimental evidence has appeared indicating a role for polaritons in organic optoelectronic devices . This may be related to the fact that often the molecular layers used are amorphous. − Here we investigate a polycrystalline film of the non-fullerene acceptor ( S,S )-BTP-4F ( 1 ). , We show that, while for amorphous films hardly any polariton characteristics are observable, for thermally annealed polycrystalline films the reflection spectrum shows a pronounced minimum in the middle of the lowest band.…”

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confidence: 79%

Polaritons in a Polycrystalline Layer of Non-fullerene Acceptor

2023

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Non-fullerene acceptor molecules developed for organic solar cells feature a very intense absorption band in the nearinfrared. In the solid phase, the strong interaction between light and the transition dipole moment for molecular excitation should induce formation of polaritons. The reflection spectra for polycrystalline films of a non-fullerene acceptor with a thienothienopyrrolo-thienothienoindole core of the so-called Y6 type indeed show a signature of polaritons. A local minimum in the middle of the reflection band is associated with the allowed molecular transition. The minimum in reflection allows efficient entry of light into the solid, resulting in a local maximum in external quantum efficiency of a photovoltaic cell made of the pure acceptor.

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“…Apart from studying the molecular interaction, orientation and phase separation, the vertical electronic properties of the blend films are also investigated by performing film‐depth‐dependent light absorption spectroscopy (FLAS). [ 62 ] As shown in Figure a–d, from intact films (top curves) to the mostly etched films (lowest absorption curves), T4‐ and T6‐based blends display obviously distinct absorption spectra after SVA with CS 2 compared with their corresponding as‐cast ones in terms of both optical density and relative peak intensity, which could originate from the different vertical component distribution and changes in absorbing ability of donor and acceptor. By fitting the sublayer absorption from the FLAS results of the blend films using the absorption spectra of pure materials, we obtain the composition distribution along the direction of film depth (Figure 5e,f).…”

Section: Resultsmentioning

confidence: 99%

Deciphering the Role of Side‐Chain Engineering and Solvent Vapor Annealing for Binary All‐Small‐Molecule Organic Solar Cells

Chen

et al. 2022

Adv Funct Materials

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Fibrous interpenetrating network structure morphology is extremely crucial for all‐small‐molecule organic solar cells (ASM‐OSCs) in achieving high power conversion efficiency (PCE). Rational molecular design and suitable posttreatment to the film are feasible methods to accomplish this goal. Herein, two small molecule donors, namely T4 and T6, with different substituents on their selenophene conjugated units, alkyl for T4 while trialkylsilyl for T6, are developed. Both as cast devices obtain poor PCEs (≈4.5%) when blending these two donors with N3 due to the oversize phase separation. Satisfactorily, the PCEs are dramatically increased after CS2 annealing, which mainly originates from the favorable reorganization of donor and acceptor in the active layer, ultimately improving the phase separation and vertical electronic properties. As a result, the device based on trialkylsilyl‐substituted T6 acquires a remarkable PCE of 16.03%, much higher than that of the blends of alkyl‐substituted T4 and N3 (12.61%). The enhanced PCE of the T6‐based device is attributed to the deeper HOMO energy levels, more obvious fibrous interpenetrating networks, and stronger molecular interaction between T6 and N3, as compared with T4‐based ones. This study indicates that precise molecular design and the proper posttreatment process can be a brilliant approach for realizing highly efficient ASM‐OSCs.

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Film‐Depth‐Dependent Light Reflection Spectroscopy for Photovoltaics and Transistors

Cited by 9 publications

References 43 publications

End Group Effect of Asymmetric Benzodithiophene‐Based Donor with Liquid‐Crystal State for Small‐Molecule Binary Solar Cell

End Group Effect of Asymmetric Benzodithiophene‐Based Donor with Liquid‐Crystal State for Small‐Molecule Binary Solar Cell

Polaritons in a Polycrystalline Layer of Non-fullerene Acceptor

Deciphering the Role of Side‐Chain Engineering and Solvent Vapor Annealing for Binary All‐Small‐Molecule Organic Solar Cells

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