Efficient Polymer Solar Cells Based on Benzothiadiazole and Alkylphenyl Substituted Benzodithiophene with a Power Conversion Efficiency over 8%

Zhang, Maojie; Gu, Yu; Guo, Xia; Liu, Feng; Zhang, Shaoqing; Huo, Lijun; Russell, Thomas P.; Hou, Jianhui

doi:10.1002/adma.201301494

Cited by 309 publications

(232 citation statements)

References 61 publications

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“…[1][2][3][4] Much remains nevertheless to be learned about how light is converted to charges and subsequent current in those devices. Typically, an electrondonating conjugated polymer is blended with an electronaccepting fullerene in the photovoltaic active layer, spontaneously forming an interpenetrating network known as the bulk heterojunction (BHJ).…”

Section: Introductionmentioning

confidence: 99%

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

et al. 2014

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Light-induced charge formation is essential for the generation of photocurrent in organic solar cells. In order to gain a better understanding of this complex process, we have investigated the femtosecond dynamics of charge separation upon selective excitation of either the fullerene or the polymer in different bulk heterojunction blends with well-characterized microstructure. Blends of the pBTTT and PBDTTPD polymers with PCBM gave us access to three different scenarios: either a single intermixed phase, an intermixed phase with additional pure PCBM clusters, or a three-phase microstructure of pure polymer aggregates, pure fullerene clusters and intermixed regions. We found that ultrafast charge separation (by electron or hole transfer) occurs predominantly in intermixed regions, while charges are generated more slowly from excitons in pure domains that require diffusion to a charge generation site.The pure domains are helpful to prevent geminate charge recombination, but they must be sufficiently small not to become exciton traps. By varying the polymer packing, backbone planarity and chain length, we have shown that exciton diffusion out of small polymer aggregates in the highly efficient PBDTTPD:PCBM blend occurs within the same chain and is helped by delocalization.

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Section: Introductionmentioning

confidence: 99%

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

et al. 2014

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“…The samples were excited with an excess energy ranging from 0.1 to 1.4 eV compared to the 1.8 eV polymer absorption edge. We have previously found that extremely low excitation fluence (<4 μJ/ cm 2 ) is necessary to avoid laser-induced exciton annihilation and charge recombination artifacts for PBDTTPD-based samples. 7 With an even improved experimental sensitivity, we have now carefully recorded all data below this threshold and verified that the dynamics for each measurement are fluence-independent in this regime.…”

Section: ■ Introductionmentioning

confidence: 99%

Charge Separation Pathways in a Highly Efficient Polymer: Fullerene Solar Cell Material

Paraecattil

Banerji

2014

J. Am. Chem. Soc.

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PBDTTPD is one of the best conjugated polymers for solar cell applications (up to 8.5% efficiency). We have investigated the dynamics of charge generation in the blend with fullerene (PCBM) and addressed highly relevant topics such as the role of bulk heterojunction structure, fullerene excitation, and excess energy. We show that there are multiple charge separation pathways. These include electron transfer from photoexcited polymer, hole transfer from photoexcited PCBM, prompt (<100 fs) charge generation in intimately mixed polymer:fullerene regions (which can occur from hot states), as well as slower electron and hole transfer from excitons formed in pure PBDTTPD or PCBM domains (diffusion to an interface is necessary). Very interestingly, all the charge separation pathways are highly efficient. For example, the yield of long-lived carriers is not significantly affected by the excitation wavelength, although this changes the fraction of photons absorbed by PCBM and the amount of excess energy brought to the system. Overall, the favorable properties of the PBDTTPD:PCBM blend in terms of morphology and exciton delocalization allow excellent charge generation in all circumstances and strongly contribute to the high photovoltaic performance of the blend. ■ INTRODUCTIONOrganic solar cells based on electron-donating conjugated polymers blended with electron-accepting fullerene derivatives have reached high efficiencies beyond 8%.1−3 In order to further enhance their performance, it is essential to deeply understand the underlying photophysical processes. Highly relevant topics that need to be addressed include the role of delocalization and exciton diffusion for efficient charge generation at the donor:acceptor interface, the role of hot neutral and charge transfer states in the formation of free carriers, and the role of the fullerene as light harvester.4 Both the nanoscale structure of the bulk heterojunction (BHJ) and the photophysical dynamics must be considered to gain answers to those questions. Femtosecond transient absorption (TA) spectroscopy is an undeniably useful tool to study the dynamics of neutral excited states and photoinduced charges in the materials of interest. 5−9Here, we will show that this purely spectroscopic technique additionally yields detailed morphological insights. Our study leads to a comprehensive picture of how different charge generation pathways relate to BHJ structure.We focus the investigation on PBDTTPD (poly(benzo[1,2-b:4,5-b′]dithiophene-alt-thieno[3,4-c]pyrrole-4,6-dione), and its blend with PCBM ([6,6]-phenyl C 60 butyric acid methyl ester). The polymer is among the best performing for photovoltaic applications, with up to 8.5% efficiency.1 Recent reports on morphology control, 1,10−12 device design, 13 charge trapping, 14 long-term stability, 15 quantum calculations, 16,17 and spectroscopy 7,18−20 confirm high interest for the material. PBDTTPD also distinguishes itself from many other conjugated polymers through its very planar structure in both the ground and ex...

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“…Significant improvements have been achieved in understanding the correlations between polymer structure and photovoltaic performance, which have helped to boost the power conversion efficiency (PCE) over 7% in several well-known backbones, such as benzodithiophene (BDT) and thienothiophene (TT) (PBDT-TT) [15][16][17][18][19][20][21][22][23][24][25][26][27][28], BDT and benzothiadiazole (BT) (PBDT-BT) [29,30], BDT and thienopyrroledione (TPD) (PBDT-TPD) [31], etc.…”

Section: Introductionmentioning

confidence: 99%

Influence of the alkyl substitution position on photovoltaic properties of 2D-BDT-based conjugated polymers

Yao

Fan

et al. 2015

Sci. China Mater.

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Efficient Polymer Solar Cells Based on Benzothiadiazole and Alkylphenyl Substituted Benzodithiophene with a Power Conversion Efficiency over 8%

Cited by 309 publications

References 61 publications

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

The influence of microstructure on charge separation dynamics in organic bulk heterojunction materials for solar cell applications

Charge Separation Pathways in a Highly Efficient Polymer: Fullerene Solar Cell Material

Influence of the alkyl substitution position on photovoltaic properties of 2D-BDT-based conjugated polymers

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