am6b14804_si_001.pdf (243.62 kB)
Effect of Heterocyclic Anchoring Sequence on the Properties of Dithienogermole-Based Solar Cells
journal contribution
posted on 2017-02-10, 00:00 authored by Bright Walker, Daehee Han, Mijin Moon, Song Yi Park, Ka-Hyun Kim, Jin Young Kim, Changduk YangThe
synthesis and characterization of two new small molecular donor materials,
DTGe(ThFBTTh2)2 and DTGe(FBTTh3)2, are presented for application in organic solar cells. These
two materials represent structural evolutions of the high-efficiency,
dithienogermole (DTGe)-cored small molecule DTGe(FBTTh2)2, in which the conjugation length in the backbone was
extended by incorporating additional thiophene units. Using the same
molecular framework, we have evaluated how the anchoring sequence
of heterocyclic units influences material properties and function
in solar cell devices. It was found that incorporating additional
thiophene units into the backbone, regardless of the position in the
molecular platform, caused a small reduction in band gaps; however,
both highest occupied molecular orbitals and lowest unoccupied molecular
orbital energy bands were at lower energies when the thiophenes were
incorporated near the terminus of the molecule. The film morphologies
of both materials could be controlled by either thermal or solvent
vapor annealing to yield phase separation on the order of tens of
nanometers and improved crystallinity. Peak power–conversion
efficiencies of 3.6% and 3.1% were obtained using DTGe(ThFBTTh2)2 and DTGe(FBTTh3)2, after
solvent vapor treatment and thermal annealing, respectively. Our study
provides a detailed analysis of how the ordering sequence of heterocyclic
building blocks influences the properties and function of organic
solar cells.