Competition between Fullerene Aggregation and Poly(3-hexylthiophene) Crystallization upon Annealing of Bulk Heterojunction Solar Cells

Wu, Wei-Ru; Jeng, U‐Ser; Su, Chun‐Jen; Wei, Kung‐Hwa; Su, Ming-Shin; Chiu, Mao-Yuan; Chen, Chun-Yu; Su, Wei-Bin; Su, Chi‐Cheung; Su, An‐Chung

doi:10.1021/nn2010816

Cited by 205 publications

(322 citation statements)

References 50 publications

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“…21 The time to complete PCBM diffusion at room temperature was not negligible, around 300 s. On the other hand, Su et al reported that PCBM diffusion dominated P3HT crystallization in the thermal-annealing process. 5 Our previous WAXS data showed that, when the drying time was relatively short, only P3HT crystallization peaks were observed. 21 As the drying time was increased, signs of PCBM crystallization appeared, and the intensity of the P3HT crystallization peaks decreased.…”

Section: Discussionmentioning

confidence: 95%

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Effect of Drying Time on Morphology and Photovoltaic Characteristics of Polymer Solar Cells of Bis-PCBM/P3HT Composites

Nagai

Gao

Huang

et al. 2016

ECS J. Solid State Sci. Technol.

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Slow drying has been proposed as a way to improve the performance of polymer solar cells (PSCs) where the drying time for the coated films is increased using a condensed solvent vapor atmosphere. This work investigated the slow drying mechanism by using PSCs consisting of poly(3-hexylthiophene-2,5-diyl) (P3HT) and bis-[6,6]-phenyl-C61-butyric acid methyl ester (bis-PCBM) and focusing on the phase-separated morphology of bulk heterojunction films. With conventional spin casting, the power conversion efficiency (PCE) of the cells was very low (0.83%). The application of slow drying resulted in notable improvements in the short-circuit current density (5.85 → 8.07 mA/cm 2 ) and fill factor (0.12 → 0.55). Optimization of the thermal annealing and cathode interfacial conditions resulted in a high PCE of 4.05%. As the drying time was increased, the P3HT domains changed from connected band-like shapes to small separated ball-like shapes. The mechanism for this effect of slow drying on the bis-PCBM/P3HT cell characteristics is understood as follows: The slow drying causes the P3HT domains to separate into small pieces, which causes the area of the p−n interfaces to increase, resulting in an increase in free carrier generation and increased the short-circuit current density of PSCs. Organic photovoltaics have been actively studied as a major candidate for use in next-generation solar cells due to the several advantages they possess, including light weight, thin film, and low material cost.1-3 In particular, polymer solar cells (PSCs) can be made by applying a solution of p-type polymers and n-type fullerene-based small molecules, meaning that PSCs do not require expensive vacuum equipment, which can potentially reduce processing costs. The efficiency of PSCs has been drastically improved over the past decade. A cell efficiency of more than 10% has already been reported. 4 However, further improvement in efficiency is crucial for practical use.The performance of PSCs depends not only on the materials used but also their processing conditions. Thermal annealing 5-8 and solvent annealing 9-11 are representative techniques for improving solar cell performance. These methods have been extensively studied, and their effects on the short-circuit current density (J sc ) of PSCs have been clarified. They enhance the crystallinity of the constituent materials 5,6,9,10 and thereby increase the carrier mobility, leading to higher J sc .Unfortunately, these methods are problematic. Thermal annealing can only be applied to certain polymers, and solvent annealing requires an extremely long processing time (normally several hours). 10Another proposed method is "slow drying," in which the drying time of the coated films is reduced by increasing the solvent vapor pressure of the film coating atmosphere. [12][13][14][15] This method also effectively increases the J sc of PSCs. While this method resembles solvent annealing, it has a much shorter treatment time (10−20 min). Therefore, from the viewpoint of mass-manufacturing, slow drying has...

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Section: Discussionmentioning

confidence: 95%

“…Various types of thermal annealing effects have been proposed, including crystallinity improvement, 5 cathode interface segregation, 6,7,25 domain coalescence, 8 and domain distribution changing. 6,25 Among these candidate effects, the improvement of crystallinity is particularly important for our bis-PCBM/P3HT cells.…”

Section: Discussionmentioning

confidence: 99%

Effect of Drying Time on Morphology and Photovoltaic Characteristics of Polymer Solar Cells of Bis-PCBM/P3HT Composites

Nagai

Gao

Huang

et al. 2016

ECS J. Solid State Sci. Technol.

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“…To this end, solvent vapor annealing (SVA) has been explored in recent years [134][135][136][137][138][139]. SVA is a versatile method, where a thin film is exposed to an atmosphere of solvent vapor diffusing into the deposited layer, the extent of which is dependent on and thus controllable by exposure time [134].…”

Section: Polar Solvent Annealingmentioning

confidence: 99%

Towards High Performance Organic Photovoltaic Cells: A Review of Recent Development in Organic Photovoltaics

2014

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Organic photovoltaic cells (OPVs) have been a hot topic for research during the last decade due to their promising application in relieving energy pressure and environmental problems caused by the increasing combustion of fossil fuels. Much effort has been made toward understanding the photovoltaic mechanism, including evolving chemical structural motifs and designing device structures, leading to a remarkable enhancement of the power conversion efficiency of OPVs from 3% to over 15%. In this brief review, the advanced progress and the state-of-the-art performance of OPVs in very recent years are summarized. Based on several of the latest developed approaches to accurately detect the separation of electron-hole pairs in the femtosecond regime, the theoretical interpretation to exploit the comprehensive mechanistic picture of energy harvesting and charge carrier generation are discussed, especially for OPVs with bulk and multiple heterojunctions. Subsequently, the novel structural designs of the device architecture of OPVs embracing external geometry modification and intrinsic structure decoration are presented. Additionally, some approaches to further increase the efficiency of OPVs are described, including thermotics and dynamics modification methods. Finally, this review highlights the challenges and prospects with the aim of providing a better understanding towards highly efficient OPVs.

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“…[13][14][15][16] Effi cient OPVs are in general characterised by structures that exist over a series of length-scales, including organisation at molecular length-scales and the formation of nanoscale percolated networks, with each length-scale having an important infl uence on the processes of photocurrent generation and charge extraction. To optimise BHJ morphology and create an OPV device having a high PCE requires control over many different parameters, including the choice of solvent, the conditions of fi lm casting and the possible application of post-fi lm deposition techniques.Several studies [17][18][19][20][21][22][23][24][25] have applied a range of techniques to probe the formation and evolution of morphology in polymer:fullerene blend fi lms during various stages in their preparation, drying and post processing in order to gain insight into the dynamic mechanisms that drive morphology evolution. [ 26 ] In addition to an improved physical understanding of such processes, the information obtained is likely to be of signifi cant importance if such materials and devices undergo commercialisation and manufacture, as real-time process control will be a critical requirement.…”

mentioning

confidence: 99%

Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution Casting

Pearson

Wang

Dunbar

et al. 2013

Adv Funct Materials

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659www.MaterialsViews.com wileyonlinelibrary.com . IntroductionThe ability to process photovoltaic devices using solution-based techniques is an attractive proposition [ 1,2 ] owing to the potential for such devices to be manufactured over large areas at low cost. [ 3 ] Organic photovoltaic (OPV) devices are one category of solution processable photovoltaics that have seen a rapid rise in power conversion effi ciency (PCE) [ 4,5 ] and operating lifetime [ 6 ] in recent years, bringing the technology closer to the specifi cations deemed necessary for commercial viability. [ 7,8 ] The photoactive semiconducting layer within these devices is typically composed of a blend of a conjugated polymer and a functionalised fullerene, forming a self-assembled bulk-heterojunction (BHJ) architecture. In addition to the electronic properties of the constituent semiconductors, the structure of the BHJ has been demonstrated to signifi cantly infl uence the efficiency of photocurrent generation. [9][10][11][12] It is presently believed that BHJ fi lms are characterised by a partially phase separated nanoscale morphology, with co-existing regions of pure polymer, pure fullerene and a mixed polymer/ fullerene phase all being present. [13][14][15][16] Effi cient OPVs are in general characterised by structures that exist over a series of length-scales, including organisation at molecular length-scales and the formation of nanoscale percolated networks, with each length-scale having an important infl uence on the processes of photocurrent generation and charge extraction. To optimise BHJ morphology and create an OPV device having a high PCE requires control over many different parameters, including the choice of solvent, the conditions of fi lm casting and the possible application of post-fi lm deposition techniques.Several studies [17][18][19][20][21][22][23][24][25] have applied a range of techniques to probe the formation and evolution of morphology in polymer:fullerene blend fi lms during various stages in their preparation, drying and post processing in order to gain insight into the dynamic mechanisms that drive morphology evolution. [ 26 ] In addition to an improved physical understanding of such processes, the information obtained is likely to be of signifi cant importance if such materials and devices undergo commercialisation and manufacture, as real-time process control will be a critical requirement. To date, the majority of Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution CastingAndrew J. Pearson ,* Tao Wang , Alan D. F. Dunbar , Hunan Yi , Darren C. Watters , David M. Coles , Paul A. Staniec , Ahmed Iraqi , Richard A. L. Jones , and David G. Lidzey * The evolution of fi lm structure is reported during solution casting of PCDTBT:PC 70 BM 1:4 wt%, a polymer:fullerene blend system that fi nds application in an organic photovoltaic device. Using the complimentary techniques of grazing-incidence wide-angle X-ray scattering and spectroscopic ellipsometry, a number of distinct proc...

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Competition between Fullerene Aggregation and Poly(3-hexylthiophene) Crystallization upon Annealing of Bulk Heterojunction Solar Cells

Cited by 205 publications

References 50 publications

Effect of Drying Time on Morphology and Photovoltaic Characteristics of Polymer Solar Cells of Bis-PCBM/P3HT Composites

Effect of Drying Time on Morphology and Photovoltaic Characteristics of Polymer Solar Cells of Bis-PCBM/P3HT Composites

Towards High Performance Organic Photovoltaic Cells: A Review of Recent Development in Organic Photovoltaics

Morphology Development in Amorphous Polymer:Fullerene Photovoltaic Blend Films During Solution Casting

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