title: Synergistic Effects of Morphological Control and Complementary Absorption in Efficient All-Small-Molecule Ternary-Blend Solar Cells.
abstract: In this study, we combined two small-molecule donors-a diketopyrrolopyrrole-based small molecule (SMD) and a benzodithiophene-based molecule (BDT6T)-with [6,6]-phenyl-C61-butyric acid methyl ester (PC61BM) to form ternary blend solar cells. The power conversion efficiency of the binary SMD:PC61BM bulk heterojunction solar cell improved from 4.57 to 6.28% after adding an appropriate amount BDT6T as a guest. We attribute this 37% improvement in device performance to the complementary absorption behavior of BDT6T and SMD, as evidenced by the increase in the short circuit current. After addition of BDT6T to form the ternary blend, the crystallinity and morphology of the active layer were enhanced. For example, the features observed in the ternary active layers were finer than those in the binary blends. This means that BDT6T as a third component in the ternary blend has effective role on both the absorption and the morphology. In addition, adding BDT6T to form the ternary blend also led to an increase in the open-circuit voltage. Our findings suggest that the preparation of such simple all-small-molecule ternary blends can be an effective means of improving the efficiency of photovoltaic devices.
authors.affiliation: Department of Engineering and System Science, National Tsing-Hua University , Hsinchu 30013, Taiwan, Republic of China.|Nanoscience and Technology Program, Taiwan International Graduate Program, Academia Sinica and National Tsing-Hua University Hsinchu, Taiwan, Republic of China.|Research Center for Applied Sciences, Academia Sinica , Taipei 115, Taiwan, Republic of China.
authors.forename: Mahmoud E
authors.initials: ME
authors.lastname: Farahat
authors.affiliation: Research Center for Applied Sciences, Academia Sinica , Taipei 115, Taiwan, Republic of China.
authors.forename: Dhananjaya
authors.initials: D
authors.lastname: Patra
authors.affiliation: Department of Engineering and System Science, National Tsing-Hua University , Hsinchu 30013, Taiwan, Republic of China.
authors.forename: Chih-Hao
authors.initials: CH
authors.lastname: Lee
authors.affiliation: Research Center for Applied Sciences, Academia Sinica , Taipei 115, Taiwan, Republic of China.
authors.forename: Chih-Wei
authors.initials: CW
authors.lastname: Chu
keywords: bulk heterojunction; morphology; organic photovoltaics; small molecules; ternary solar cells