Comparison of the Photovoltaic Characteristics and Nanostructure of Fullerenes blended with Conjugated Polymers with Siloxane-Terminated and Branched Aliphatic Sidechains
- Authors
- Kim, Do Hwan; Ayzner, Alexander L.; Appleton, Anthony L.; Schmidt, Kristin; Mei, Jianguo); Toney, Michael F.; Bao, Zhenan
- Issue Date
- Dec-2012
- Publisher
- AMER CHEMICAL SOC
- Keywords
- organic photovoltaics; siloxane side chain; DIO; molecular packing; thin-film morphology; X-ray scattering
- Citation
- CHEMISTRY OF MATERIALS, v.25, no.3, pp.431 - 440
- Indexed
- SCIE
SCOPUS
- Journal Title
- CHEMISTRY OF MATERIALS
- Volume
- 25
- Number
- 3
- Start Page
- 431
- End Page
- 440
- URI
- https://scholarworks.bwise.kr/hanyang/handle/2021.sw.hanyang/163871
- DOI
- 10.1021/cm303572d
- ISSN
- 0897-4756
- Abstract
- All-organic bulk heterojunction solar cells based on blends of conjugated polymers with fullerenes have recently surpassed the 8% efficiency mark and are well on their way to the industrially relevant similar to 45% threshold. Using a low band-gap conjugated polymer, we have recently shown that polymer side chain engineering can lead to dramatic improvement in the in-plane charge carrier mobility. In this article, we investigate the effectiveness of siloxy side chain derivatization in controlling the photovoltaic performance of polymer: [6,6]-phenyl-C[71]-butyric acid methyl ester (PC71BM) blends and hence its influence on charge transport in the out-of-plane direction relevant for organic solar cells. We find that, in neat blends, the photocurrent of the polymer with siloxy side chains (PII2T-Si) is 4 times greater than that in blends using the polymer with branched aliphatic side chains (PII2T-ref). This difference is due to a larger out-of-plane hole mobility for PII2T-Si brought about by a largely face-on crystallite orientation as well as more optimal nanoscale polymer:PC71BM mixing. However, upon incorporating a common processing additive, 1,8-diiodooctane (DIO), into the spin-casting blend solution and following optimization, the PII2T-ref:PC71BM OPV device performance undergoes a large improvement and becomes the better-performing device, almost independent of DIO concentration (>1%). We find that the precise amount of DIO plays a larger role in determining the efficiency of PII2T-Si:PC71BM, and even at its maximum, the device performance lags behind optimized PII2T-ref:PC71BM blends. Using a combination of atomic force microscopy and small- and wide-angle X-ray scattering, we are able to elucidate the morphological modifications associated with the DIO-induced changes in both the nanoscale morphology and the molecular packing in blend films.
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