Determining Material-Specific Morphology of Bulk-Heterojunction Organic Solar Cells Using AFM Phase Imaging

Jovanov, Vladislav; Yumnam, Nivedita; Müller, Arne; Gruber, Mathias; Wagner, Veit

doi:10.1021/acs.jpcc.7b01924

Cited by 17 publications

(16 citation statements)

References 52 publications

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“…To observe the morphology changes of smithsonite before and after sulfidization, AFM height and phase imaging were used. In the AFM phase images, the presence of different materials at the surface of the sample was indicated by differences in contrast, providing additional information; hence, phase imaging is suitable for such a study [27,28].…”

Section: Afm Observationmentioning

confidence: 99%

Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Liu

Pei

Liu³

et al. 2020

Minerals

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Sulfidization is required in the amine flotation of smithsonite; however, the sulfidization mechanism of smithsonite is still not fully understood. In this work, X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and UV–vis diffuse reflectance spectroscopy (UV–vis DRS) were used to characterize sulfidized and unsulfidized smithsonite. The XPS and UV–vis DRS analyses showed that smithsonite sulfidization is a transformation of ZnCO3 to ZnS on the smithsonite surfaces. However, this transformation is localized, resulting in the coexistence of ZnCO3 and ZnS or in the formation of ZnS island structures on the sulfidized smithsonite surfaces. AFM height imaging showed that sulfidization can substantially change the surface morphology of smithsonite; in addition, AFM phase imaging demonstrated that sulfidization occurs locally on the smithsonite surfaces. Based on our findings, it can be concluded that smithsonite sulfidization is clearly a heterogeneous solid–liquid reaction in which the solid product attaches at the surfaces of unreacted smithsonite. Smithsonite sulfidization involves heterogeneous nucleation and growth of ZnS nuclei. Moreover, the ZnS might nucleate and grow preferentially in the regions with high reactivity, which might account for the formation of ZnS island structures. In addition, sphalerite-structured ZnS is more likely to be the sulfidization product of smithsonite under flotation-relevantconditions, as also demonstrated by the results of our UV–vis DRS analyses. The results of this study can provide deeper insights into the sulfidization mechanism of smithsonite.

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Section: Afm Observationmentioning

confidence: 99%

Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Liu

Pei

Liu³

et al. 2020

Minerals

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“…The relatively high PCBM content in the blend can lead to an imbalanced electron‐to‐hole mobility ratio, making difficult to transport holes due to large domains . Reported µ value through SCLC measurements of PTB7 yielded the value 5.9 × 10 −4 cm 2 V −1 s −1 , for [70]PCBM is reported 1 ×10 −3 cm 2 V −1 s −1 and for the blend (PTB7:[70]PCBM) is in the range of 3.2 × 10 −4 − 2 × 10 −4 cm 2 V −1 s −1 ; from pc‐AFM local J – V plot (Figure a) and by using Equation , a mobility µ value of 1.69 × 10 −4 cm 2 V −1 s −1 for the PTB7:[70]PCBM blend is determined, which is in good agreement with that one reported in the literature. Figure b shows a typical J – V plot of OPVs devices under the AM1.5 illumination condition .…”

Section: Resultsmentioning

confidence: 93%

Semiconducting Polymer Thin Films Used in Organic Solar Cells: A Scanning Tunneling Microscopy Study

Caballero‐Quintana

Maldonado

Menéses-Nava

et al. 2018

Adv Elect Materials

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The widely used semiconducting polymers poly(3,4‐ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) (PH1000), poly(3‐hexylthiophene‐2,5‐diyl) (P3HT), and Poly[[4,8‐bis[(2‐ethylhexyl)oxy]benzo[1,2‐b:4,5‐b′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno[3,4‐b]thiophenediyl]] (PTB7) for organic photovoltaic (OPV) cells, are deposited on highly ordered pyrolytic graphite substrates and investigated by scanning tunneling microscopy (STM) under the liquid/solid interface technique. PEDOT:PSS film morphology shows an ellipsoidal shape of PEDOT surrounded by PSS with 4 nm size. STM images of P3HT reveal that films tend to form well‐defined crystalline domains with an average interchain distance around 1.41 nm and chain length ≈41 nm. PTB7 chains are self‐aggregated by using chlorobenzene as solvent; however, when using 1‐phenyloctane with 3% of 1,8‐diiodooctane, these chains show a worm‐like pattern with a distance of ≈2 nm between backbone chains and a chain length of ≈90 nm. For P3HT and PTB7 based OPVs, local J–V plots are determined from photoconductive atomic force microscopy (pc‐AFM) measurements and fitted with the modified Mott−Gurney equation, the reached parameters are correlated with those achieved from the macroscopic J–V graphs. Active films of OPVs cells based on PTB7 are also analyzed by using AFM phase imaging showing domains size of 80–120 nm. This current STM analysis can elucidate some new important insights on polymer film formation and morphology and therefore, their influence on the OPV performance.

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“…The corresponding potentials of buried layers were imaged into their respective contact potential difference (CPD) levels by KPFM scanning [ 17 ]. It should be noted that boundary of each layer can only be assigned by the phase image; thus, the dark line between the PCDTBT:PCBM BHJ layer and anode PEDOS:PSS layer in KPFM image is not an interface of these two layers [ 18 ]. Depth profile of CPD can be obtained by row-wise averaging of measured KPFM signals of Fig.…”

Section: Resultsmentioning

confidence: 99%

Potential Dip in Organic Photovoltaics Probed by Cross-sectional Kelvin Probe Force Microscopy

Lee

Kong²

2018

Nanoscale Res Lett

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Cross-sectional potential distribution of high open-circuit voltage bulk heterojunction photovoltaic device was measured using Kelvin probe force microscopy. Potential drop confined at cathode interface implies that photo-active layer is an effective p-type semiconductor. Potential values in field-free region show wide variation according to log-normal distribution. This potential dip prone to have holes captured during the diffusive motion, which can increase bimolecular recombination, while potential gradient in depletion region makes this potential dip smaller and the captured holes easily escape from dip region by Schottky barrier lowering.

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Determining Material-Specific Morphology of Bulk-Heterojunction Organic Solar Cells Using AFM Phase Imaging

Cited by 17 publications

References 52 publications

Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Improved Understanding of the Sulfidization Mechanism in Amine Flotation of Smithsonite: An XPS, AFM and UV–Vis DRS Study

Semiconducting Polymer Thin Films Used in Organic Solar Cells: A Scanning Tunneling Microscopy Study

Potential Dip in Organic Photovoltaics Probed by Cross-sectional Kelvin Probe Force Microscopy

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