Conjugated polyelectrolyte (CPE) interfacial layers present a powerful way to boost the I-V characteristics of organic photovoltaics. Nevertheless, clear guidelines with respect to the structure of high-performance interlayers are still lacking. In this work, impedance spectroscopy is applied to probe the dielectric permittivity of a series of polythiophene-based CPEs. The presence of ionic pendant groups grants the formation of a capacitive double layer, boosting the charge extraction and device efficiency. A counteracting effect is the diminishing affinity with the underlying photoactive layer. To balance these two effects, we found copolymer structures containing nonionic side chains to be beneficial.
Organic photovoltaics (OPV) have attracted great interest as a solar cell technology with appealing mechanical, aesthetical, and economies-of-scale features. To drive OPV toward economic viability, low-cost, large-scale module production has to be realized in combination with increased top-quality material availability and minimal batch-to-batch variation. To this extent, continuous flow chemistry can serve as a powerful tool. In this contribution, a flow protocol is optimized for the high performance benzodithiophene-thienopyrroledione copolymer PBDTTPD and the material quality is probed through systematic solar-cell evaluation. A stepwise approach is adopted to turn the batch process into a reproducible and scalable continuous flow procedure. Solar cell devices fabricated using the obtained polymer batches deliver an average power conversion efficiency of 7.2 %. Upon incorporation of an ionic polythiophene-based cathodic interlayer, the photovoltaic performance could be enhanced to a maximum efficiency of 9.1 %.
Abstract. In this manuscript, the Kumada catalyst transfer polymerization (KCTP) of cyclopenta [2,1-b;3,4-b']dithiophene (CPDT), a monomer consisting of two fused thiophene entities, is investigated. It is shown that this polymerization follows a controlled chain-growth mechanism. Furthermore, the formation of block-copolymers with poly(3-alkylthiophene)s is investigated, and it is shown that these block-copolymers can be formed if 3-alkylthiophene is used as the first block and CPDT as the second. The resulting all-conjugated block-copolymers consist of two blocks with substantially different electronic and physical properties and it is shown that the blocks influence each other, resulting in a unique material with different properties compared to a blend.2
Although controlled polymerization procedures for conjugated polymers have considerable advantages with respect to molar mass and end group control, the material scope has been very limited, in particular considering block copolymers and donor-acceptor type all-conjugated polymers, imposing considerable challenges upon the synthetic polymer community. In this work, a push-pull monomer consisting of a thiophene (donor) and a pyridine (acceptor) unit is synthesized and subsequently polymerized via Kumada catalyst-transfer polymerization using a nickel catalyst (GRIM polymerization). In this way, an alternating donor-acceptor copolymer is obtained via a chain-growth mechanism. Furthermore, an all-conjugated block copolymer containing a poly(3-hexylthiophene) block and the alternating copolymer is successfully prepared in a one-pot procedure as well. The diblock structure is confirmed by comparison of the thermal, electrochemical and spectroscopic properties of the block copolymer and its constituting polymer parts.
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