Surface segregation at the aluminum interface of poly(3-hexylthiophene)/fullerene solar cells

Orimo, Akiko; Masuda, K.; Honda, Satoshi; Benten, Hiroaki; Ito, Shinzaburo; Ohkita, Hideo; Tsuji, Hiroshi

doi:10.1063/1.3294290

Cited by 122 publications

(141 citation statements)

References 15 publications

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“…6,7 It has been explained by the difference in component segregation at the cathode interfaces. In a postannealed cell, PCBM, which segregates at the cathode interfaces, can control the leakage current by blocking holes and promotes electron injection into the cathodes.…”

Section: Discussionmentioning

confidence: 99%

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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: 99%

“…Thermal annealing [5][6][7][8] and solvent annealing [9][10][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.…”

mentioning

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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“…These two annealing stages have different effects for different device structures with and without LiF buffer layers. Pre-annealing has been reported to improve the efficiency of solar cells containing LiF [16], whereas post-annealing has been reported to improve the efficiency of solar cells that do not contain LiF [7][8][9]11]. Li et al have reported that the LiF buffer layer is modified by the post-annealing [16].…”

Section: Introductionmentioning

confidence: 99%

“…On the basis of the similar characteristics of C 60 and PCBM, the mobility can be reasonably inferred to decrease with increasing such electron scattering. Anion formation decreases J sc and concomitantly decreases V oc [11]. Anion formation should also decrease V oc because of the shift in energy levels at the interfaces [19,20].…”

Section: Mechanism Of Performance Degradationmentioning

confidence: 99%

“…One of the most widely studied organic thin-film solar cells employs an active layer of blend films with a poly(3-hexylthiophene) (P3HT) electron donor and a phenyl-C 61 -butyric acid methyl ester (PCBM) electron acceptor. The performance of solar cells has been improved using a variety of methods, such as the insertion of a lithium-fluoride (LiF) buffer layer [4][5][6], thermal annealing [7][8][9][10][11], solvent annealing [12,13], and the use of mixed solvents [14]. In particular, the effects of LiF insertion and thermal annealing have drastically improved the performance such as power-conversion efficiency (PCE) [15].…”

Section: Introductionmentioning

confidence: 99%

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ESR Study of Degradation Mechanism Due to Charge Formation in Polymer Solar Cells

Marumoto

Dong

Yabusaki

2016

J. Photopol. Sci. Technol.

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The degradation mechanism of polymer solar cells containing a lithium-fluoride (LiF) buffer layer created by a thermal annealing process at different temperatures was studied using an electron spin resonance (ESR) and current-voltage characteristics. The device structure was indium-tin-oxide (ITO)/poly(3,4-ethylenedioxythiophene): poly(4-styrenesulfonate) (PEDOT:PSS)/poly(3-hexylthiophene):phenyl-C 61 -butyric acid methyl ester (P3HT:PCBM)/LiF/Al. When the post-annealing temperature increased, the performance of the cells decreased and the ESR signal from PCBM radical anions was enhanced dramatically. The formation of a greater number of anions enhanced the electron scattering and caused an energy-level shift at the interface. These effects led to degradation in the device performance.

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Solubility, Miscibility, and the Impact on Solid‐State Morphology

Machui

Brabec

2012

Semiconducting Polymer Composites

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Surface segregation at the aluminum interface of poly(3-hexylthiophene)/fullerene solar cells

Cited by 122 publications

References 15 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

ESR Study of Degradation Mechanism Due to Charge Formation in Polymer Solar Cells

Solubility, Miscibility, and the Impact on Solid‐State Morphology

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