The Fabrication of Ordered Bulk Heterojunction Solar Cell by Nanoimprinting Lithography Method Using Patterned Silk Fibroin Mold at Room Temperature

Nanoscale Research Letters, Dec 2015

The performance of organic solar cell is greatly determined by the nanoscale heterojunction morphology, and finding a practical method to achieve advantageous nanostructure remains a challenge. We demonstrate here that ordered bulk heterojunction (OBHJ) solar cell can be fabricated assisted by a simple, cost-effective nanoimprinting lithography method using patterned silk fibroin film mold at room temperature. The P3HT nanogratings were achieved by nanoimprinting lithography (NIL) process, and phenyl-C61-butyric acid methyl ester (PCBM) was spin-coated on the top of P3HT nanogratings. The conducting capacity of P3HT nanograting film has little difference compared with the unimprinted film in the vertical direction, due to the same edge-on chain alignment. However, it can be found that the fabrication of OBHJ nanostructure using room temperature NIL technique with patterned silk fibroin mold is able to promote optical absorption, interfacial area, and bicontinuous pathway. Therefore, the ordered heterojunction morphology plays an important part in improving device performance due to efficient exciton diffusion, dissociation, and reducing charge recombination rate.

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The Fabrication of Ordered Bulk Heterojunction Solar Cell by Nanoimprinting Lithography Method Using Patterned Silk Fibroin Mold at Room Temperature

Ding et al. Nanoscale Research Letters The Fabrication of Ordered Bulk Heterojunction Solar Cell by Nanoimprinting Lithography Method Using Patterned Silk Fibroin Mold at Room Temperature Guangzhu Ding 0 Qianqian Jin 0 Qing Chen 0 Zhijun Hu Jieping Liu 0 0 College of Chemistry and Materials Science, Huaibei Normal University , Huaibei 235000 , China The performance of organic solar cell is greatly determined by the nanoscale heterojunction morphology, and finding a practical method to achieve advantageous nanostructure remains a challenge. We demonstrate here that ordered bulk heterojunction (OBHJ) solar cell can be fabricated assisted by a simple, cost-effective nanoimprinting lithography method using patterned silk fibroin film mold at room temperature. The P3HT nanogratings were achieved by nanoimprinting lithography (NIL) process, and phenyl-C61-butyric acid methyl ester (PCBM) was spin-coated on the top of P3HT nanogratings. The conducting capacity of P3HT nanograting film has little difference compared with the unimprinted film in the vertical direction, due to the same edge-on chain alignment. However, it can be found that the fabrication of OBHJ nanostructure using room temperature NIL technique with patterned silk fibroin mold is able to promote optical absorption, interfacial area, and bicontinuous pathway. Therefore, the ordered heterojunction morphology plays an important part in improving device performance due to efficient exciton diffusion, dissociation, and reducing charge recombination rate. Nanoimprint lithography; Nanopattern; Ordered bulk heterojunction; Silk fibroin film Background The organic solar cells based on the bulk heterojunction (BHJ) have received considerable attention as an attractive alternative to silicon photovoltaic cell as they have achieved favorable characteristics, such as low cost, flexibility, and simple process [ 1, 2 ]. As long as there is light absorption, the excitons are generated, diffused, and dissociated at the interface between donor and acceptor materials and then transported to their respective electrodes, forming the external circuit [3]. Therefore, the performance of organic solar cell is greatly determined by the nanoscale heterojunction morphology within active layer. One of the ideal structures in active layer is to construct an ordered bulk heterojunction (OBHJ) morphology consisting of vertically bicontinuous and interdigitized heterojunction between donor and acceptor materials, to enable both efficient exciton separation and transport [ 4–6 ]. Despite OBHJ nanostructure morphology contributes to the solar cell performance and a comprehensive understanding of fundamental principle, finding a practical method to achieve this nanostructure remains a challenge to now. Several techniques, such as polymer nanowires, block copolymer, and nanoimprinting lithography (NIL), have been reported to fabricate OBHJ solar cell [ 7–9 ]. Among these techniques, thermal NIL is investigated as a promising method to define nanostructures due to its high resolution, effective cost, and simple process [ 10, 11 ]. NIL method is able to replicate the nanostructures defined on a hard mold into some soft materials, such as semiconducting polymers [ 12–19 ], ferroelectric polymers [ 20, 21 ], and proteins [ 22, 23 ]. Therefore, the control of nanoimprint mold is of great importance in the fabrication of OBHJ solar cell by NIL technique. Some traditional molds with high resolution over a large area, such as silicon mold or anodic aluminum oxide mold, are reported to apply; however, they are usually timeconsuming, have complicated process, have simple fragility, crush or deformed easily, and do not to meet the need of commercial application. It is desired to seek a costeffective and simple process method for mold fabrication. Silk fibroin film from the Bombyx mori silkworm has attracted considerable interest owing to its biological, mechanical, and optical properties [ 24–27 ]. Silk fibroin film is able to be easily patterned by several techniques [ 22, 28 ] and has been applied to biocompatible and degradable electronic or photonic devices [ 29, 30 ]. In nanoimprinting process, the application of heat and pressure to a patterned silk fibroin mold, which is fabricated by control of the water content and beta sheet crystallinity within silk film, can be accomplished to transfer nanostructure to other soft materials [23]. Silk fibroin film was chosen for the nanoimprinting mold mainly due to its advantageous material properties as well as simple and inexpensive production process [ 31, 32 ]. The Bombyx mori silkworm which is used to produce patterned silk fibroin film comes from broad source and is cheap. Silk fibroin film is able to be easily patterned, and the fabrication process is simple and convenient, fully meet to the demand of large area production. Then, there is little interaction between silk film and conjugated polymer, for example, p (...truncated)


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Guangzhu Ding, Qianqian Jin, Qing Chen, Zhijun Hu, Jieping Liu. The Fabrication of Ordered Bulk Heterojunction Solar Cell by Nanoimprinting Lithography Method Using Patterned Silk Fibroin Mold at Room Temperature, Nanoscale Research Letters, 2015, pp. 491, Volume 10, Issue 1, DOI: 10.1186/s11671-015-1194-7