In this study, the well-defined coil-rod-coil triblock copolymer poly(4-vinyltriphenylamine)b-poly(3-hexylthiophene)-b-poly(4-vinyltriphenylamin) (PTPA-P3HT-PTPA) was used as a surfactant for P3HT/PCBM (1:1) based solar cells. The power conversion efficiency of the device was enhanced from 3.9 to 4.4% in the presence of the 0-5% PTPA-P3HT-PTPA under illumination of AM 1.5G (100 mW/cm 2 ). The morphology variation and the balance of the hole/electron mobility accounted for such enhancement. In the P3HT/PCBM/PTPA-P3HT-PTPA ternary blends, the fiber-like structure was observed for surfactant ratios of 0-5%, while a sphere-like nanostructure was observed for the surfactant ratio of 1.5%. The sphere-like nanostructure led to a smaller domain size and enhanced interfacial area for charge separation as compared to the fiber-like structure. On the other hand, the increased hole mobility in the blend with the addition of PTPA-P3HT-PTPA resulted in the balanced hole and electron mobility (μ e /μ h ∼1.7 in comparison to the ratio of 3.6 without the surfactant). The incorporated PTPA-P3HT-PTPA surfactant not only extended the lifetime of solar cells but also reduced the PCBM aggregation upon annealing, resulting in better thermal stability. The DSC result confirmed the selective miscibility of the PTPA coil segment with PCBM. These results demonstrated the superior compatibilizing effect of the rod-coil triblock copolymers for solar cell applications.
Random copolyimides, PI–PBIX, with
different compositions of 4,4′-(hexafluoroisopropylidene)diphthalic
anhydride (6FDA), N,N′-bis(4-aminophenyl)-3,4,9,10-perylenebis(dicarboximide) (PBI), and 4,4′-diamino-4″-methyltriphenylamine
(AMTPA) were designed and synthesized for resistive-switching
memory device applications. By varying the feeding ratio of monomers, PI–PBIX (where X = 0, 1, 2.5, 5, and 10
for molar composition of repeating units containing PBI) showed tunable optical and electronic properties through the charge
transfer between AMTPA and PBI. Also, the
memory devices prepared from PI–PBIX sandwiched
between ITO and Al electrodes exhibited the tunable electrical bistability
from the volatile to nonvolatile write once read many-times (WORM)
memory characteristics as the PBI composition increased.
The OFF/ON electrical switching transition was mainly attributed to
the charge-transfer mechanism for charge-separated high conductance,
based on the analysis of density function theory. Also, the volatility
of PI–PBIX device depended on the stability of
charge-transfer complex and charge trapping sites. The deep LUMO energy
level of the PBI moiety increased the back-charge-transfer
energy barrier and prevented recombination of segregated charges even
through applying the high negative and positive voltage. The study
revealed that the memory characteristics could be tailored from the
donor–acceptor composition in the random copolyimides.
We explore the memory device characteristics of the all-conjugated diblock copolythiophenes, poly(3-hexylthiophene)-block-poly(3-phenoxymethylthiophene) (P3HT-b-P3PT), and their blends with PCBM. The field-effect transistors prepared from P3HT-b-P3PT showed a significant hysteresis between the forward and backward gate-bias scans in the transfer curve, indicating the occurrence of charge trapping. The charge trapping may have occurred within the amorphous P3PT domains dispersed in the block copolythiophene by preventing charge transport. P3HT 52 -b-P3PT 39 and P3HT 102 -b-P3PT 37 exhibited dynamic random access memory (DRAM) behavior in the sandwich configuration of ITO/P3HT-b-P3PT/Al, whereas P3HT only showed semiconductor characteristics, suggesting the significant effect of the amorphous P3PT segments on the electrical switching behavior. By blending a small amount (5-10 wt%) of PCBM into P3HT-b-P3PT of different block ratios (P3HT 52 -b-P3PT 39 , P3HT 102 -b-P3PT 37 , and P3HT 89 -b-P3PT 23 ), the memory devices showed a writeonce-read-many times (WORM) behavior with the switching voltages of À2.6 to À3.3 V and high ON/ OFF ratios (10 5 to 10 7 ). The mechanism associated with the memory characteristics was the charge transfer from the P3HT-b-P3PT donor to the PCBM acceptor, which stabilized the charge separated state and retained the high conductance state for a long time during the ON stage. These experimental results provide a new strategy of designing all-conjugated block copolymers for advanced memory device applications.
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