Environmentally Friendly Solvent‐Processed Organic Solar Cells that are Highly Efficient and Adaptable for the Blade‐Coating Method

Zhao, Wenchao; Zhang, Shaoqing; Zhang, Yun; Li, Sunsun; Liu, Xiaoyu; He, Chang; Zheng, Zhong; Hou, Jianhui

doi:10.1002/adma.201704837

Cited by 181 publications

(141 citation statements)

References 54 publications

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“…Another striking advantage of the bilayer structure is that both the donor and acceptor layers can be processed separately, thus resulting in less dependence on the processing condition, for example, the D/A ratio, additive, and even the processing solvent. [41] These results show that the bilayer structure is truly a potential candidate for the fabrication of printed OSCs. The data are shown in Figure 4 and Table 2.…”

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confidence: 75%

High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

Dong

Zhang

Xie

et al. 2018

Advanced Energy Materials

158

157

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power conversion efficiency (PCE) of BHJ devices strongly depends on phase separation of the donor and acceptor. However, the formation of BHJ morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. To achieve high-performance devices, much effort has been devoted to delicately control the morphology of the active layer (such as the blend ratio between the donor and acceptor, [9][10][11] the type of solvent, [12][13][14] the type and amount of processing additive, [15][16][17] and thermal and solvent annealing [18][19][20] ) to obtain optimal interpenetrated nanoscale phase separation. What is worse, the morphology control becomes much more challenging when the device area is scaled up, for example, the morphology of printed film may vary drastically when the processing condition changes. For this reason, there are typically large performance drops when OPV devices are scaled up to large area or processed using printing techniques. [21,22] Moreover, green solvent is a prerequisite for the commercialization of OSCs. However, for the BHJ structure, the solubility and miscibility of both the donor and acceptor must be taken into consideration together, which limits the selection of a processing solvent. Most OSCs were processed with toxic halogen solvents, and only a few high-performances donor/acceptor combinations were reported in the literature using low toxicity/nontoxic solvents.In contrast, sequential deposition of the donor and acceptor materials followed by post thermal annealing can lead to a similar BHJ morphology and reasonably efficient OSC devices. The interpenetration between donor and acceptor during the solution processing ensures the D/A interfaces for separation of the charges. [23][24][25] The bilayer structure should be more favorable for charge transport as the separated charges can easily transport to each electrode through the D or A layer with low possibility of recombination. [26][27][28] In addition, as both donor and acceptor layers can be processed and optimized independently, this bilayer structure should show less dependence on the D/A ratio, solvent, additive, etc., when compared with the BHJ structure. These properties make the bilayer structure very attractive for achieving high-performance OSCs and While the performance of laboratory-scale organic solar cells (OSCs) continues to grow over 13%, the development of high-efficiency large area OSCs still lags. One big challenge is that the formation of bulk heterojunction morphology is an extremely complicated process and the formed morphology is also a highly delicate balance involving many parameters such as domain size, purity, miscibility, etc. The morphology control becomes much more challenging when the device area is scaled up. In this work, a highly efficient (12.9%) nonfullerene organic solar cell processed using a sequential bilayer deposition method from nonhalogenated solvents, is reported. Using this bi...

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confidence: 75%

High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

Dong

Zhang

Xie

et al. 2018

Advanced Energy Materials

158

157

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“…As shown in Figure 4a, PCP-2F-Li exhibits an outstanding tolerance to thickness variation in fabricating OSCs; i.e., when the PCP-2F-Li thickness increased from 4 to 15 nm, the devices only showed a slight drop in J sc , resulting in a PCE of 12.0% (Table S2, Inspired by the excellent thickness insensitivity of PCP-2F-Li, we further processed the CPEs through the blade-coating method to make large-area devices. [50,51] In conclusion, we demonstrated the crucial effect of fluorination in enhancing the WF of CPEs, and developed a series of AIL materials. The J-V curves of the device and the corresponding photovoltaic parameters are shown in Figure 4c.…”

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confidence: 78%

Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

Lü

Liao

et al. 2019

Advanced Energy Materials

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cathode interlayer materials that are successfully used in the efficient OSCs, anode interlayer (AIL) materials with satisfactory performances are rather rare. [15][16][17] Although several materials such as poly (3,4-ethylenedioxythiophene):(styrene sulfonate) (PEDOT:PSS) and metal oxides have been widely used as AILs, the acidic nature of PEDOT:PSS and the energy-consuming preparation process of metal oxides limit their practical uses in OSCs. [18][19][20][21] At present, the lack of ideal AILs has seriously impeded the pace toward practical application of OSCs.Currently, the enhancement of work function (WF) is the most critical issue for the development of AILs. [22,23] Many research results indicated that WFs have significant influence on the open-circuit voltage (V oc ) of the devices. [24,25] For instance, Vasilopoulou et al. enhanced the WF of molybdenum oxide AILs from 5.4 to 5.9 eV by controlling the hydrogenation degree of Mo element, by which the V oc of the device increased from 0.59 to 0.65 V. [26] Moreover, Irwin et al. prepared a NiO x AIL with a high WF of 5.4 eV, and achieved a V oc increment of 14 mV for the device. [27] However, in recent years, with the situation that the highest occupied molecular orbital (HOMO) levels of donors in fullerenefree devices are constantly downshifted for achieving high V oc , [28,29] most previously developed AILs cannot satisfy the new demands for modifying efficient OSCs because the low WFs of these materials give rise to large energy offsets with donors, which causes interfacial barrier for hole collection and leads to serious V oc loss. [30] Thus, it is particularly urgent to explore new approaches that can further enhance the WF of AILs.Among various materials, conjugated polyelectrolytes (CPEs) are promising candidates as AIL materials due to their neutral pH, excellent charge transporting capacity, and good filmforming property. [31,32] Unlike PEDOT:PSS and metal oxides, the chemical structure of CPEs can be readily modified through synthetic chemistry, which provides great opportunities for improving the WF of AILs. For example, Lee et al. enhanced the WF of p-PFP-X from 4.97 to 5.26 eV by tuning electric dipoles of the cation-anion pairs on the side chains of CPEs, and obtained an increased PCE of 9.2% in the OSC device. [33] However, these methods merely achieved limited WF enhancement and most of the developed AILs only worked well in fullerene-based OSCs. [34] Moreover, protonic acid doping has Since the highest occupied molecular orbital (HOMO) level of donors in organic solar cells (OSCs) is being constantly downshifted for achieving high open-circuit voltage (V oc ), a further enhancement of the anode work function (WF) is required. Herein, an effective approach of fluorinationis demonstrated to simultaneously improve the WF and transparency for anode interlayer (AIL) material. By fluorination, in combination with the dialysis treatment in LiCl solution, the WF of PCP-2F-Li could be significantly enhanced from 4.86 to 5.0 eV, as compared to PCP-Na...

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“…[19,20,[28][29][30][31][32][33][34][35][36][37][38][39][40] To the best of our knowledge, all these high-performance donor polymers are alternating donor-acceptor (D-A) type copolymers, which are exclusively based on benzo[1,2-b:4,5-b′]dithiophene (BDT) donor unit [41] copolymerized with a few acceptor counits, such as 5,6-difluoro-2-alkyl-2H-benzo[d] [1,2,3]triazole (FTAZ), [42] benzo[1,2-c:4,5-c′]-dithiophene-4,8-dione (BDD) [43] etc. [19,20,[28][29][30][31][32][33][34][35][36][37][38][39][40] To the best of our knowledge, all these high-performance donor polymers are alternating donor-acceptor (D-A) type copolymers, which are exclusively based on benzo[1,2-b:4,5-b′]dithiophene (BDT) donor unit [41] copolymerized with a few acceptor counits, such as 5,6-difluoro-2-alkyl-2H-benzo[d] [1,2,3]triazole (FTAZ), [42] benzo[1,2-c:4,5-c′]-dithiophene-4,8-dione (BDD) [43] etc.…”

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confidence: 99%

Phthalimide‐Based High Mobility Polymer Semiconductors for Efficient Nonfullerene Solar Cells with Power Conversion Efficiencies over 13%

Chen

Koh

et al. 2018

Advanced Science

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Highly efficient nonfullerene polymer solar cells (PSCs) are developed based on two new phthalimide‐based polymers phthalimide‐difluorobenzothiadiazole (PhI‐ffBT) and fluorinated phthalimide‐ffBT (ffPhI‐ffBT). Compared to all high‐performance polymers reported, which are exclusively based on benzo[1,2‐b:4,5‐b′]dithiophene (BDT), both PhI‐ffBT and ffPhI‐ffBT are BDT‐free and feature a D‐A1‐D‐A2 type backbone. Incorporating a second acceptor unit difluorobenzothiadiazole leads to polymers with low‐lying highest occupied molecular orbital levels (≈−5.6 eV) and a complementary absorption with the narrow bandgap nonfullerene acceptor IT‐4F. Moreover, these BDT‐free polymers show substantially higher hole mobilities than BDT‐based polymers, which are beneficial to charge transport and extraction in solar cells. The PSCs containing difluorinated phthalimide‐based polymer ffPhI‐ffBT achieve a substantial PCE of 12.74% and a large V oc of 0.94 V, and the PSCs containing phthalimide‐based polymer PhI‐ffBT show a further increased PCE of 13.31% with a higher J sc of 19.41 mA cm−2 and a larger fill factor of 0.76. The 13.31% PCE is the highest value except the widely studied BDT‐based polymers and is also the highest among all benzothiadiazole‐based polymers. The results demonstrate that phthalimides are excellent building blocks for enabling donor polymers with the state‐of‐the‐art performance in nonfullerene PSCs and the BDT is not necessary for constructing such donor polymers.

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Environmentally Friendly Solvent‐Processed Organic Solar Cells that are Highly Efficient and Adaptable for the Blade‐Coating Method

Cited by 181 publications

References 54 publications

High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

High‐Performance Large‐Area Organic Solar Cells Enabled by Sequential Bilayer Processing via Nonhalogenated Solvents

Significant Effect of Fluorination on Simultaneously Improving Work Function and Transparency of Anode Interlayer for Organic Solar Cells

Phthalimide‐Based High Mobility Polymer Semiconductors for Efficient Nonfullerene Solar Cells with Power Conversion Efficiencies over 13%

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