This work exposes the importance of testing a polymers active layer thickness tolerance as small modifications to a polymers structure can radically change its ability to stack/pack in the BHJ which is reflected in thick active layer OSCs.
Side-chain
sequence enabled regioisomeric acceptors, bearing different
side-chain sequences on the same conjugated backbone, are herein reported.
Two regioregular polymers PTBI-1 and PTBI-2 and one regiorandom polymer
PTBI-3 were synthesized from these two regioisomeric acceptors for
a comparative study. UV–vis–NIR absorption spectroscopy
and electrochemical study confirmed similar frontier molecular orbital
levels of the three polymers in their solid state. More intriguingly,
absorption profiles suggest that the sequence of side chains greatly
governs the aggregation behaviors. Furthermore, the PTBI-2 film shows
larger ordered domains than PTBI-1 and PTBI-3 films, as supported
by AFM and GIWAXS measurements. As a result, PTBI-2-based FET devices
achieved an average hole mobility of 1.37 cm2 V–1 s–1, much higher than the two polymers with other
side-chain sequences. The regiorandom PTBI-3 exhibited the lowest
average hole mobility of 0.27 cm2 V–1 s–1. This study highlights the significant impact
of side-chain sequence regioisomerism on aggregation behaviors, morphologies,
and subsequently charge transport properties of donor–acceptor
type conjugated polymers.
The existence of point defects, holes, and corrugations
(macroscopic
defects) induces high catalytic potential in graphene and its derivatives.
We report a systematic approach for microscopic and macroscopic defect
density optimization in excimer laser-induced reduced graphene oxide
by varying the laser energy density and pulse number to achieve a
record detection limit of 7.15 nM for peroxide sensing. A quantitative
estimation of point defect densities was obtained using Raman spectroscopy
and confirmed with electrochemical sensing measurements. Laser annealing
(LA) at 0.6 J cm–2 led to the formation of highly
reduced graphene oxide (GO) by liquid-phase regrowth of molten carbon
with the presence of dangling bonds, making it catalytically active.
Hall-effect measurements yielded a mobility of ∼200 cm2 V–1 s–1. An additional
increase in the number of pulses at 0.6 J cm–2 resulted
in deoxygenation through the solid-state route, leading to the formation
of holey graphene structure. The average hole size showed a hierarchical
increase, with the number of pulses characterized with multiple microscopy
techniques, including scanning electron microscopy, atomic force microscopy,
and transmission electron microscopy. The exposure of edge sites due
to high hole density after 10 pulses supported the formation of proximal
diffusion layers, which led to facile mass transfer and improvement
in the detection limit from 25.4 mM to 7.15 nM for peroxide sensing.
However, LA at 1 J cm–2 with 1 pulse resulted in
a high melt lifetime of molten carbon and the formation of GO characterized
by a high resistivity of 3 × 10–2 Ω-cm,
which was not ideal for sensing applications. The rapid thermal annealing
technique using a batch furnace to generate holey graphene results
in structure with uneven hole sizes. However, holey graphene formation
using the LA technique is scalable with better control over hole size
and density. This study will pave the path for cost-efficient and
high-performance holey graphene sensors for advanced sensing applications.
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