Solution-processed photocells based on low energy-gap polymer and unmodified C70 composites from halogen-free solvent exceeding 5% power conversion efficiency

Tada, Kazuya

doi:10.1016/j.solmat.2015.06.029

Cited by 18 publications

(15 citation statements)

References 27 publications

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“…The fitting of current density-voltage characteristics with a simple one-diode equivalent circuit model suggests that the increased PCE is mainly due to increased shunt resistance and decreased saturation current of the diode in the model, both of which contribute to the reduction of the internal loss of photocarriers in the photocell. The present results,together with the latest report of the PCE over 5 % in a photocell with a similar material system [19], indicate that the bulk heterojunction photocells using unmodified fullerene prepared with halogen-free solvent are potentially useful for the permanent power source of indoor devices such as wireless sensor node. …”

Section: Discussionsupporting

confidence: 65%

Characteristics of PTB7:C70 bulk heterojunction photocell prepared with halogen-free solvent at low light illumination

Tada

2016

Polym. Bull.

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Increasing social demands for clean and cheap renewable energy sources have been promoting the researches on polymer photocells based on bulk heterojunction composites consisting of conjugated polymers and fullerenes. The replacement of traditional chloroaromatic solvents such as chlorobenzene with a halogen-free solvent 1,2,4-trimethylbenzene (TMB), which enables the preparation of bulk heterojunction composites with unmodified fullerenes, potentially reduces the economic and environmental costs of organic bulk heterojunction photocells. In this study, photovoltaic characteristics of PTB7:C 70 bulk heterojunction photocells prepared with TMB at low light intensity are studied. It has been found that the power conversion efficiency (PCE) of a photocell with ITO/PEDOT:PSS/PTB7:C 70 / Al structure whose PCE is approximately 3 % under AM1.5G 1 sun (100 mW/ cm -2 ) illumination increases with decreased illumination light intensity, being 5.9 % at 10 -3 sun illumination. An analysis of current-voltage characteristics suggests that the increased PCE is mainly due to increased shunt resistance and decreased saturation current of the diode in the model. The results indicate that the solution-processed organic photocell based on unmodified fullerene prepared with halogen-free solvent is a promising candidate for environmental-friendly device for indoor light harvesting.

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Section: Discussionsupporting

confidence: 65%

Characteristics of PTB7:C70 bulk heterojunction photocell prepared with halogen-free solvent at low light illumination

Tada

2016

Polym. Bull.

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“…Although devices based on the pristine fullerene C70 have been reported for both polymer and small-molecule donors with a powerconversion efficiency PCE of 5.1 % and 5.9 %, respectively, [7,8] the most competitive results are currently achieved with the more soluble PCBMs, which can yield a PCE of more than 10 %. [9] As low cost is the major selling point of organic photovoltaics, it is desirable to choose the most cost-effective materials.…”

Section: / 18mentioning

confidence: 99%

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

et al. 2015

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cells 2 / 18Fullerenes are an intriguing class of organic semiconductors that feature a high electron affinity and exceptional charge transport properties, desirable for a number of thin-film optoelectronic applications such as field-effect transistors (FETs) and organic solar cells. Despite their desirable solid-state properties a major disadvantage of pristine C60 and C70 is the seemingly poor solubility in organic solvents, [1,2] which however can be substantially improved by attaching exohedral moieties to the fullerene cage, albeit at the expense of a high electron mobility. [3][4][5] In addition, pristine fullerenes suffer from the strong tendency to crystallize during solvent removal, which complicates formation of continuous thin films. As a result, substituted fullerenes, such as in particular phenyl-Cx-butyric acid methyl esters (PCBMs; x = 61 or 71), are by far the most widely studied electron acceptor material for organic photovoltaic applications. The trade-off between increased solubility and reduced electron mobility has so far been acceptable for thin-film solar cells because the latter is still sufficiently high to not limit solar cell performance, which more strongly depends on the precise active layer nanostructure. However, as future improvements in device efficiency rely on thick active layers and high-mobility materials, [6] the use of pristine fullerenes may prove to be advantageous provided that solubility issues can be addressed and a favorable nanostructure can be achieved.The most efficient active layer nanostructure of organic solar cells is the bulkheterojunction, which is typically prepared by co-processing a fullerene acceptor and a suitable donor from a common organic solvent. Although devices based on the pristine fullerene C70 have been reported for both polymer and small-molecule donors with a powerconversion efficiency PCE of 5.1 % and 5.9 %, respectively, [7,8] the most competitive results are currently achieved with the more soluble PCBMs, which can yield a PCE of more than 10 %. [9] As low cost is the major selling point of organic photovoltaics, it is desirable to choose the most cost-effective materials. In this regard, the use of PCBMs as the electron 3 / 18 acceptor is not optimal. The additional synthesis steps required to prepare these derivatives from pristine fullerenes considerably increase the energy footprint, which implies a higher environmental impact as well as an overall higher materials cost. For instance, Anctil et al.calculated a life cycle embodied energy as low as about 8 GJ kg -1 for the as-synthesized C60:C70 mixture, which increases to 25 GJ kg -1 for C60 and 38 GJ kg -1 for C70 after separation and electronic-grade purification. [10] In contrast, preparation of substituted fullerenes consumes significantly more energy, i.e. 65 GJ kg -1 and 90 GJ kg -1 for electronic-grade PC61BM and PC71BM, respectively. Therefore, the use of pristine fullerenes and in particular C60:C70 mixtures may result in significant energy savings provided that the ability to f...

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“…The total concentration of the composite solution was 30 g l

^{- 1}

. Since the PTB7‐Th sample used for the present study was less soluble in TMB than that used in the previous study (), the composite solution had to be warmed upon a hotplate at 100

^{\circ}

C for a few hours prior to the spin‐coating. A 1.0 g l

^{- 1}

stock solution of PFN dissolved in methanol containing 2 vol.% of acetic acid was diluted with pure methanol to obtain 0.3 g l

^{- 1}

PFN solution.…”

Section: Methodsmentioning

confidence: 99%

“…Thus, the realization of solution‐processed polymer photocells with unmodified fullerene by using a halogen‐free solvent seems to be an attractive research subject. The author has shown that a not‐so‐common halogen‐free solvent 1,2,4‐trimethylbenzene (TMB), also known as pseudocumene, enables the production of polymer bulk heterojunction composites with unmodified fullerene such as C

_{60}

and C

_{70}

for photocells . Recently, TMB has attracted special attention of researchers as a promising green solvent for polymer photocells .…”

Section: Introductionmentioning

confidence: 99%

“…In this study, the characteristics of photocells with PTB7‐Th:C

_{70}

bulk heterojunction composite, which show the power conversion efficiency (PCE) close to 5% at AM 1.5G 1 sun illumination () under low‐light illumination, are studied. A sublinear dependence of the short‐circuit photocurrent on the illumination light intensity, as well as increased fill‐factor (FF) under reduced illumination, is identified as the key to the improvement of PCE under low light.…”

Section: Introductionmentioning

confidence: 99%

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Characteristics of PTB7‐Th:C bulk heterojunction photocells under low‐light illumination: Critical effect of dark parallel resistance

Tada

2017

Physica Status Solidi (a)

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Solution-processed organic photocell is one of the most promising candidates for the permanent power source for wireless devices. Since the device is not necessarily to be placed outdoor, and indoor light is generally weaker than outdoor light by 2-3 orders of magnitude, the characterization of the photocell under low-light illumination is important for this purpose. In this study, bulk heterojunction photocells based on a lowenergy gap polymer poly [[4,8-bis[5-(2-ethylhexyl) [3,4-b]thiophenediyl]] (PTB7-Th) as well as unmodified C 70 prepared with a halogen-free solvent 1,2,4-trimethylbenzene, are characterized under low-light illumination. The combination of a halogen-free solvent with an unmodified fullerene potentially provides a way to develop environmentally friendly organic photocells. It is found that the photocells show higher power conversion efficiency (PCE) under lower light illumination intensity. That is, a device showing PCE of 4.9% under 1 sun illumination shows PCE over 9% at 3' 10 −4 sun. A sublinear dependence of the short-circuit photocurrent to the light intensity, as well as the increased fill-factor at reduced illumination, is found to be a key to the high PCE at low-light. The latter originates from the photoconduction in the composite. The critical effect of dark parallel resistance on the low-light performance of the photocells is also demonstrated.1 Introduction Photocells based on bulk heterojunction composites consisting of conjugated polymers and fullerenes are attracting much interest of the researchers, partly because the compatibility with low-temperature solution-based process makes them promising candidates for large-area low-cost renewable energy source in the near future [1][2][3][4]. The development of conjugated polymers such as poly [[4,8-bis[(2ethylhexyl)oxy]benzo [1,2-b:4,5-b ]dithiophene-2,6-diyl][3fluoro-2-[(2-ethylhexyl)carbonyl]thieno[3,4-b]thiophenediyl]] (PTB7) and poly[[4,8-bis[5-(2-ethylhexyl) thiophene-2yl]benzo[1,2-b:4,5-b'f]dithiophene-2,6-diyl][3-fluoro-2-[(2ethylhexyl)carbonyl]thieno [3,4-b]thiophenediyl]] (PTB7-Th) is pushing up the performance of this class of photocells [5,6].The use of highly soluble fullerene derivatives such as [6,6]-phenyl-C 71 -butyric acid methyl ester (C 70 -PCBM), as

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Solution-processed photocells based on low energy-gap polymer and unmodified C70 composites from halogen-free solvent exceeding 5% power conversion efficiency

Cited by 18 publications

References 27 publications

Characteristics of PTB7:C70 bulk heterojunction photocell prepared with halogen-free solvent at low light illumination

Characteristics of PTB7:C70 bulk heterojunction photocell prepared with halogen-free solvent at low light illumination

High‐Entropy Mixtures of Pristine Fullerenes for Solution‐Processed Transistors and Solar Cells

Characteristics of PTB7‐Th:C bulk heterojunction photocells under low‐light illumination: Critical effect of dark parallel resistance

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