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A method is reported for the controlled synthesis of device-grade semiconducting polymers, utilizing a droplet-based microfl uidic reactor. Using poly(3-hexylthiophene) (P3HT) as a test material, the reactor is shown to provide a controlled and stable environment for polymer synthesis, enabling control of molecular weight via tuning of fl ow conditions, reagent composition or temperature. Molecular weights of up to 92 000 Da are readily attainable, without leakage or reactor fouling. The method avoids the usual deterioration in materials quality that occurs when conventional batch syntheses are scaled from the sub-gram level to higher quantities, with a prototype fi ve-channel reactor producing material of consistent molecular weight distribution and high regioregularity ( > 98%) at a rate of ≈ 60 g/day. The droplet-synthesized P3HT compares favorably with commercial material in terms of absorption spectrum, polydispersity, regioregularity, and crystallinity, yielding power conversion effi ciencies of up to 4% in bulk heterojunction solar cells with [6,6]-phenyl-C61-butyric acid methyl ester.

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Dithienogermole‐co‐thieno[3,4‐c]pyrroledione (DTG‐TPD) polymers incorporating chemically cross‐linkable sidechains are reported and their properties compared to a parent polymer with simple octyl sidechains. Two cross‐linking groups and mechanisms are investigated, UV‐promoted radical cross‐linking of an alkyl bromide cross‐linker and acid‐promoted cationic cross‐linking of an oxetane cross‐linker. It is found that random copolymers with a 20% incorporation of the cross‐linker demonstrate a higher performance in bulk heterojunction solar cells than the parent polymer, while 100% cross‐linker incorporation results in deterioration in device efficiency. The use of 1,8‐diiodooctane (DIO) as a processing additive improves as‐cast solar cell performance, but is found to have a significant deleterious impact on solar cell efficiency after UV exposure. The instability to UV can be overcome by the use of an alternative additive, 1‐chloronapthalene, which also promotes high device efficiency. Cross‐linking of the polymer is investigated in the presence and absence of fullerene highlighting significant differences in behavior. Intractable films cannot be obtained by radical cross‐linking in the presence of fullerene, whereas cationic cross‐linking is successful.

particularly successful strategy has been the donor-acceptor approach, in which an electron rich donor is co-polymerized with an electron defi cient acceptor. The co-polymerization has shown to assist the reduction of the band gap by molecular orbital hybridization. [1][2][3][4][5] Computational density functional theory (DFT) calculations on donor-acceptor co-polymers have typically shown that the HOMO is delocalized over the conjugated backbone whilst the LUMO is more strongly localized on the acceptor co-monomer. [6][7][8] Therefore, tuning of either the electron rich or electron defi cient unit is an effective method to engineer the band gap and energetic levels of the resulting co-polymers.Electron [9][10][11][12][13] Previously, we have reported the synthesis of high molecular weight PDTG-BT and demonstrated PCE of 4.5% in OPV devices with promisingly high short circuit currents ( J sc ) of 18.6 mA cm −2 after annealing. [ 13 ] At the same period of time, other groups have also reported the synthesis of lower molecular weight PDTG-BT that exhibits somewhat The PCE of PDTG-PT is further improved to 6.6% when the device architecture is modifi ed from normal to inverted. Therefore, PDTG-PT is an ideal candidate for application in tandem solar cells confi guration due to its high effi ciency at very low band gaps ( E g opt = 1.32 eV). Finally, the 6.6% PCE is the highest reported for all the co-polymers containing bridged bithiophenes with 5-member fused rings in the central core and possessing an E g opt below 1.4 eV.