title: Following the nanostructural molecular orientation guidelines for sulfur versus thiophene units in small molecule photovoltaic cells.
abstract: In bulk heterojunction (BHJ) organic photovoltaics, particularly those using small molecules, electron donor and/or electron acceptor materials form a distributed network in the photoactive layer where critical photo-physical processes occur. Extensive research has recently focused on the importance of sulfur atoms in the small molecules. Little is known about the three-dimensional orientation of these sulfur atom-containing molecules. Herein, we report on our research concerning the heterojunction textures of the crystalline molecular orientation of small compounds having sulfur-containing units in the side chains, specifically, compounds known as DR3TSBDT that contain the alkylthio group and DR3TBDTT that does not. The improved performance of the DR3TBDTT-based devices, particularly in the photocurrent and the fill factor, was attributed to the large population of donor compound crystallites with a favorable face-on orientation along the perpendicular direction. This orientation resulted in efficient charge transport and a reduction in charge recombination. These findings underscore the great potential of small-molecule solar cells and suggest that even higher efficiencies can be achieved through materials development and molecular orientation control.
authors.affiliation: POSTECH Organic Electronics Laboratory, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, Republic of Korea. cep@postech.ac.kr.
authors.forename: Yu Jin
authors.initials: YJ
authors.lastname: Kim
authors.affiliation: POSTECH Organic Electronics Laboratory, Department of Chemical Engineering, Pohang University of Science and Technology, Pohang, 790-784, Republic of Korea. cep@postech.ac.kr.
authors.forename: Chan Eon
authors.initials: CE
authors.lastname: Park