title: Sequential processing: control of nanomorphology in bulk heterojunction solar cells.
abstract: Bulk heterojunction organic photovoltaic devices based on poly[N-9''-hepta-decanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole) (PCDTBT)/[6,6]-phenyl C(70) butyric acid methyl ester (PC(70)BM) can be successfully fabricated by a sequential solution deposition process. When the top layer is deposited from an appropriate cosolvent, the PC(70)BM penetrates a predeposited bottom layer of PCDTBT during the spin-casting process, resulting in an interdiffused structure with a layer-evolved bulk heterojunction (LE-BHJ) nanomorphology. The PCDTBT:PC(70)BM LE-BHJ solar cells prepared with an optimized cosolvent ratio have comparable power conversion efficiency to the conventional BHJ solar cells. The nanomorphology of the optimized PCDTBT:PC(70)BM LE-BHJ mixture was found to have better vertical connectivity than the conventional BHJ material.
authors.affiliation: Center for Polymers and Organic Solids, University of California at Santa Barbara, Santa Barbara, California 93106-5090, United States.
authors.forename: Dong Hwan
authors.initials: DH
authors.lastname: Wang
authors.forename: Ji Sun
authors.initials: JS
authors.lastname: Moon
authors.forename: Jason
authors.initials: J
authors.lastname: Seifter
authors.forename: Jang
authors.initials: J
authors.lastname: Jo
authors.forename: Jong Hyeok
authors.initials: JH
authors.lastname: Park
authors.forename: O Ok
authors.initials: OO
authors.lastname: Park
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Heeger