Enhancing the performance of solution-processed bulk-heterojunction solar cells using hydrogen-bonding-induced self-organization of small molecules.
Small-molecule solar-cell performance is highly sensitive to the crystallinity and intermolecular connectivity of the molecules. In order to enhance the crystallinity for the solution-processed small molecule, it is possible to make use of carboxylic acid end-functional groups to drive hydrogen-bonding-induced π-π stacking of conjugated molecules. Herein, we report the synthesis and characterization of quarterthiophenes with carboxylic acid as end groups. The formation of hydrogen bonds between neighboring acid groups gives rise to a pseudo-polymeric structure in the molecules, which leads to substantial improvement in the organization and crystallinity of the active layers. This resulted in a four-fold increase in the hole mobility and a two-fold improvement in the performance of the solar cell device for the acid-functionalized molecule, compared to its ester analogue. More importantly, optimal device performance for the acid-functionalized molecule was achieved for the as-cast film, thereby reducing the reliance on thermal annealing and solvent additives.
School of Materials Science and Engineering, Nanyang Technological University , Blk N4.1, Nanyang Avenue, Singapore 639798.
Kwan Hang
KH
Lam
Thelese Ru Bao
TR
Foong
Zi En
ZE
Ooi
Jie
J
Zhang
Andrew Clive
AC
Grimsdale
Yeng Ming
YM
Lam