Characterization of the mesoscopic structure in the photoactive layer of organic solar cells: A focused review

Vakhshouri, Kiarash; Kesava, Sameer Vajjala; Kozub, Derek; Gomez, Enrique D.

doi:10.1016/j.matlet.2012.08.146

Cited by 41 publications

(36 citation statements)

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“…[ 12,[29][30][31][32][33] Figure 3 shows scattering profi les as a function of scattering vector, q , which are typical for small angle scattering of polymer/fullerene mixtures. [ 10,12,22,27,[34][35][36][37][38][39][40] Assuming the scattering is dominated by structure factors, we estimate a domain spacing from the infl ection point in the data near q = 0.015 Å −1 that corresponds to an average distance between domains of approximately 40 nm. Previous work on poly(3-hexylthiophene)/PCBM fi lms suggests that at 284.4 eV contrast between pure polymer phases and mixed domains is dominant (even when fullerene aggregates are present), such that the domain spacing corresponds to the distance between polymer fi brils.…”

Section: Resultsmentioning

confidence: 99%

Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/Fullerene Solar Cells

Kesava

Fei

Rimshaw

et al. 2014

Advanced Energy Materials

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The complex microstructure of organic semiconductor mixtures continues to obscure the connection between the active layer morphology and photovoltaic device performance. For example, the ubiquitous presence of mixed phases in the active layer of polymer/fullerene solar cells creates multiple morphologically distinct interfaces which are capable of exciton dissociation or charge recombination. Here, it is shown that domain compositions and fullerene aggregation can strongly modulate charge photogeneration at ultrafast timescales through studies of a model system, mixtures of a low band‐gap polymer, poly[(4,4′‐bis(2‐ethylhexyl)dithieno[3,2‐b:2′,3′‐d]germole)‐2,6‐diyl‐alt‐(2,1,3‐benzothia‐diazole)‐4,7‐diyl], and [6,6]‐phenyl‐C71‐butyric acid methyl ester. Structural characterization using energy‐filtered transmission electron microscopy (EFTEM) and resonant soft X‐ray scattering shows similar microstructures even with changes in the overall film composition. Composition maps generated from EFTEM, however, demonstrate that compositions of mixed domains vary significantly with overall film composition. Furthermore, the amount of polymer in the mixed domains is inversely correlated with device performance. Photoinduced absorption studies using ultrafast infrared spectroscopy demonstrate that polaron concentrations are highest when mixed domains contain the least polymer. Grazing‐incidence X‐ray scattering results show that larger fullerene coherence lengths are correlated to higher polaron yields. Thus, the purity of the mixed domains is critical for efficient charge photogeneration because purity modulates fullerene aggregation and electron delocalization.

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Section: Resultsmentioning

confidence: 99%

Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/Fullerene Solar Cells

Kesava

Fei

Rimshaw

et al. 2014

Advanced Energy Materials

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“…Increasing the crystallinity results in increases of the PCBM aggregates and P3HT crystal sizes . The domain size of the P3HT crystals was approximately 15 nm by 20 nm and that of the PCBM aggregates varied from 5 nm to 15 nm …”

Section: Resultsmentioning

confidence: 99%

Microstructural behavior and failure mechanisms of organic semicrystalline thin film blends

Zhao

Awartani

O’Connor

et al. 2016

J. Polym. Sci. Part B: Polym. Phys.

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Organic thin film blends of P3HT semiconducting polymers and PCBM fullerenes have enabled large‐scale semiconductor fabrication pertaining to flexible and stretchable electronics. However, molecular packing and film morphologies can significantly alter mechanical stability and failure behavior. To further understand and identify the fundamental mechanisms affecting failure, a multiphase microstructurally based formulation and nonlinear finite‐element fracture methodology were used to investigate the heterogeneous deformation and failure modes of organic semicrystalline thin film blends. The multiphase formulation accounts for the crystalline and amorphous behavior, polymer tie‐chains, and the PCBM aggregates. Face‐on packing orientations resulted in extensive inelastic deformation and crystalline rotation, and this was characterized by ductile failure modes and interfacial delamination. For edge‐on packing orientations, brittle failure modes and film cracking were due to lower inelastic deformation and higher film stress in comparison with the face‐on orientations. The higher crystallinity of P3HT and larger PCBM aggregates associated with larger domain sizes, strengthened the film and resulted in extensive film cracking. These predictions of ductile and brittle failure are consistent with experimental observations for P3HT:PCBM films. The proposed predictive framework can be used to improve organic film ductility and strength through the control of molecular packing orientations and microstructural mechanisms. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2016, 54, 896–907

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“…Materials structure, which is often called morphology in the OPV community, has become a well-studied OPV subtopic [24,26,76,[104][105][106]. The importance of BHJ morphology may be obvious when considering the mismatch between the length scale of exciton diffusion and the thickness of the typical OPV active layer.…”

Section: Materials Structure In Opvmentioning

confidence: 99%

“…The morphology of a BHJ can depend strongly on the two components used and the casting conditions [23]. Morphology studies of BHJ systems are thus very common in the field, although there is considerable disagreement about what morphological features should lead to the highest performing solar cells [24][25][26].…”

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Organic Photovoltaics

DeLongchamp

2015

Semiconductor Materials for Solar Photovoltaic Cells

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Organic photovoltaics (OPV) describes a group of technologies wherein the active layer of a solar cell is composed of hydrocarbon-based organic materials [1][2][3]. OPV occupies a special niche among solar energy technologies in that it could potentially satisfy the growing energy needs of the world with a product that is sustainable, elementally abundant, and cheaply manufactured. OPV cells have recently seen a dramatic uptick in reported efficiencies, with power conversion efficiencies reaching ≈11 %, as shown in Fig. 6.1 [4,5]. These increases in power conversion efficiency have largely been driven by the development and discovery of new OPV active layer materials and new ways to process them. The technology has gained significant commercial attention over the past decade, as its unique attributes merit consideration for a place in the landscape of distributed energy generation devices [6]. Some of OPV advantages include a flexible form factor and facile processing, either from fluids or from vacuum deposition.At least two different device designs are often regarded as OPV technologies. The first is based on a solid-state OPV cell, having typically two organic semiconductors in a bilayer or distributed heterojunction arrangement. The second type, which will not be addressed in this chapter, is more typically called a dye-sensitized solar cell (DSSC) [7], which relies on a mesoporous electron conductor that is typically inorganic, a sensitizing dye, and an ion-conducting redox electrolyte. Unlike organic heterojunctions, the DSSC contains liquid and thus faces challenges in packaging and limited flexibility.The first report of a solid-state OPV cell was as early as 1959, when a photovoltaic effect in ≈10-μm-thick anthracene crystals was reported [8].

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Characterization of the mesoscopic structure in the photoactive layer of organic solar cells: A focused review

Cited by 41 publications

References 42 publications

Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/Fullerene Solar Cells

Domain Compositions and Fullerene Aggregation Govern Charge Photogeneration in Polymer/Fullerene Solar Cells

Microstructural behavior and failure mechanisms of organic semicrystalline thin film blends

Organic Photovoltaics

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