Morphology changes upon scaling a high-efficiency, solution-processed solar cell

Ro, Hyun Wook; Downing, Jonathan M.; Engmann, Sebastian; Herzing, Andrew A.; DeLongchamp, Dean M.; Richter, Lee J.; Mukherjee, Subhrangsu; Ade, Harald; Abdelsamie, Maged; Jagadamma, Lethy Krishnan; Amassian, Aram; Liu, Yuhang; Yan, He

doi:10.1039/c6ee01623e

Cited by 178 publications

(184 citation statements)

References 57 publications

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“…[45] We recently demonstrated excellent correlation between polymer BHJ films coated with the system and films coated via slot-die on a flexible web. [46] Based on established spin-coating protocols, we utilized DIO as a solvent additive. DIO loading studies indicate that 0.3 % is optimal for the blade-coat processes.…”

Section: Resultsmentioning

confidence: 99%

Reduced bimolecular recombination in blade-coated, high-efficiency, small-molecule solar cells

Engmann

Herzing

et al. 2017

J. Mater. Chem. A

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To realize the full promise of solution deposited photovoltaic devices requires processes compatible with high-speed manufacturing. We report the performance and morphology of blade-coated bulk heterojunction devices based on the small molecule donor p-DTS(FBTTh2)2 when treated with a post-deposition solvent vapor annealing (SVA) process. SVA with tetrahydrofuran improves the device performance of blade-coated films more than solvent additive processing (SA) with 1,8-diiodooctane. In spin-coating, SA and SVA achieve similar device performance. Our optimized, blade coated, SVA devices achieve power conversion efficiencies over 8 % and maintain high efficiencies in films up to ≈ 250 nm thickness, providing valuable resilience to small process variations in high-speed manufacturing. Using impedance spectroscopy, we show that this advantageous behavior originates from highly suppressed bimolecular recombination in the SVA-treated films. Electron microscopy and grazing-incidence X-ray scattering experiments show that SA and SVA both produce highly crystalline donor domains, but SVA films have a radically smaller domain size compared to SA films. We attribute the different behavior to variations in initial nucleation density and relative ability of SVA and SA to control subsequent crystal growth.

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Section: Resultsmentioning

confidence: 99%

Reduced bimolecular recombination in blade-coated, high-efficiency, small-molecule solar cells

Engmann

Herzing

et al. 2017

J. Mater. Chem. A

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“…[29] In-situ measurements benefit from the stationary sample and moving blade geometry, easing measurement compared to spin-coating for a variety of analysis tools such as white light transmission and reflection as well as X-ray diffraction techniques. In this study, devices consisting of benzodithiophene terthiophene rhodanine: phenyl-C71-butyric-acid-methyl ester, BTR:PC 71 BM, mass ratio 1:1 and film thickness of ≈200 nm were prepared inside a N 2 purged glove box by blade coating solutions of 60 mg total solids/mL of chloroform:chlorobenzene 1:1 by volume.…”

Section: Resultsmentioning

confidence: 99%

Film morphology evolution during solvent vapor annealing of highly efficient small molecule donor/acceptor blends

Engmann

Herzing

et al. 2016

J. Mater. Chem. A

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Solution-processable small molecule photovoltaics based on the novel molecular donor, benzodithiophene terthiophene rhodanine (BTR), recently have shown maximum power conversion efficiencies above 8 % for active layer thicknesses up to 400 nm, using post process solvent vapor annealing (SVA) with tetrahydrofuran (THF). Here we report an in-situ study on the morphology evolution during SVA using the moderate solvent THF and the good solvent chloroform (CF). The combination of real-time grazing incidence X-ray diffraction (GIXD) and grazing incidence small angle X-ray scattering (GISAXS) allows us to draw a complete picture of the evolution of crystallinity and phase purity during post process annealing. We find that the relative crystallinity compared to the as-cast films is only modestly affected by SVA and solvent choice. However, both the phase purity and the characteristic domain sizes within the film vary significantly and are controlled by the solvent quality as well as exposure time. Using THF, films with high phase purity and desirable characteristic length scales of about 30 nm can be achieved, while the use of CF rapidly leads to excessive film coarsening and less preferable domain sizes on the order of 60 nm, too large for optimized charge separation.

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“…Qualitative comparison of the 100 reflections in the GIWAXS patterns of PTB7-Th and MEH-PPV films ( Figure S4, Supporting Information) showed MEH-PPV with a broader peak indicative of more features that are randomly oriented in this film in comparison to the narrower reflection pattern of PTB7-Th. [61] For the purpose of identifying and quantifying the ordered and disordered backbone regions in the spin-coated PTB7-Th and MEH-PPV thin films, solid-state magic-angle-spinning (MAS) NMR was used to probe the structures of these polymers at a molecular level. [60] A drawback to GIWAXS, however, is that it only detects signals coming from the crystalline contents in a film and so, accurately quantifying the absolute amount of crystalline and amorphous regions in a film requires the use of additional complementary techniques.…”

Section: Quantification Of Ordered and Disordered Regions In Thin Filmentioning

confidence: 99%

Unifying Energetic Disorder from Charge Transport and Band Bending in Organic Semiconductors

Karki

Wetzelaer

Reddy

et al. 2019

Adv Funct Materials

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Characterizing the density of states (DOS) width accurately is critical in understanding the charge-transport properties of organic semiconducting materials as broader DOS distributions lead to an inferior transport. From a morphological standpoint, the relative densities of ordered and disordered regions are known to affect charge-transport properties in films; however, a comparison between molecular structures showing quantifiable ordered and disordered regions at an atomic level and its impact on DOS widths and charge-transport properties has yet to be made. In this work, for the first time, the DOS distribution widths of two model conjugated polymer systems are characterized using three different techniques. A quantitative correlation between energetic disorder from band-bending measurements and charge transport is established, providing direct experimental evidence that chargecarrier mobility in disordered materials is compromised due to the relaxation of carriers into the tail states of the DOS. Distinction and quantification of ordered and disordered regions of thin films at an atomic level is achieved using solid-state NMR spectroscopy. An ability to compare solid-state film morphologies of organic semiconducting polymers to energetic disorder, and in turn charge transport, can provide useful guidelines for applications of organic conjugated polymers in pertinent devices.

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Morphology changes upon scaling a high-efficiency, solution-processed solar cell

Abstract: Optimized spin-coating and blade-coating are found to produce similar performance yet notably different morphologies.

Cited by 178 publications

References 57 publications

Reduced bimolecular recombination in blade-coated, high-efficiency, small-molecule solar cells

Reduced bimolecular recombination in blade-coated, high-efficiency, small-molecule solar cells

Film morphology evolution during solvent vapor annealing of highly efficient small molecule donor/acceptor blends

Unifying Energetic Disorder from Charge Transport and Band Bending in Organic Semiconductors

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