title: Naphtho[2,1-b:3,4-b']dithiophene-based bulk heterojunction solar cells: how molecular structure influences nanoscale morphology and photovoltaic properties.
abstract: Organic bulk heterojunction photovoltaic devices based on a series of three naphtho[2,1-b:3,4-b']dithiophene (NDT) derivatives blended with phenyl-C71-butyric acid methyl ester were studied. These three derivatives, which have NDT units with various thiophene-chain lengths, were employed as the donor polymers. The influence of their molecular structures on the correlation between their solar-cell performances and their degree of crystallization was assessed. The grazing-incidence angle X-ray diffraction and atomic force microscopy results showed that the three derivatives exhibit three distinct nanoscale morphologies. We correlated these morphologies with the device physics by determining the J-V characteristics and the hole and electron mobilities of the devices. On the basis of our results, we propose new rules for the design of future generations of NDT-based polymers for use in bulk heterojunction solar cells.
authors.affiliation: POSTECH Organic Electronics Laboratory, Department of Chemical Engineering, Pohang University of Science and Technology, 77 Cheongam-Ro, Nam-Gu, Pohang, 790-784 (Republic of Korea).
authors.forename: Yu Jin
authors.initials: YJ
authors.lastname: Kim
authors.forename: Ye Rim
authors.initials: YR
authors.lastname: Cheon
authors.forename: Jang Yeol
authors.initials: JY
authors.lastname: Back
authors.forename: Yun-Hi
authors.initials: YH
authors.lastname: Kim
authors.forename: Dae Sung
authors.initials: DS
authors.lastname: Chung
authors.forename: Chan Eon
authors.initials: CE
authors.lastname: Park
keywords: X-ray diffraction; bulk heterojunction; nanoscale morphology; organic solar cells; polymers