Self-Seeded Growth of
Poly(3-hexylthiophene) (P3HT)
Nanofibrils by a Cycle of Cooling and Heating in Solutions
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Abstract
In spite of the recent successes in transistors and solar
cells
utilizing poly(3-hexylthiophene) (P3HT) nanofibrils, systematic analysis
on the growth kinetics has not been reported due to the lack of analytical
tools. This study proposed a simple spectroscopic method to obtain
the crystallinity of P3HT in solutions. On the basis of the analytical
approach, we found that the crystallinity hysteresis upon temperature
is a simple function of the solubility parameter difference (Δδ)
between the P3HT and the solvents. When Δδ ≥ 0.7,
a cooling (−20 °C)-and-heating (25 °C) process allowed
the preparation of solutions including 1D crystal seeds dispersed
in the solution. Simple coating of the seeded solutions completed
the growth of the seeds into long nanofibrils at the early stage of
the coating and thereby achieved almost 100% crystallinity in the
resulting films without any postannealing process. The existence of
PCBM for bulk-heterojunction (BHJ) solar cells did not affect the
nucleation and growth of the nanofibrils during the cooling-and-heating
process. The solar cells prepared from the solutions with Δδ
≥ 0.7 had solar conversion efficiencies higher than the conventional
thermally annealed cells