Flexible organic photovoltaics (OPVs) are promising power sources for wearable electronics. However, it is challenging to simultaneously achieve high efficiency as well as good stability under various stresses. Herein, we demonstrate the fabrication of highly efficient (efficiency, 13.2%) and stable OPVs based on nonfullerene blends by a single-step postannealing treatment. The device performance decreases dramatically after annealing at 90 °C and is fully recovered after annealing at 150 °C. Glass-encapsulated annealed OPVs show good environmental stability with 4.8% loss in efficiency after 4,736 h and an estimatedT80lifetime (80% of the initial power conversion efficiency) of over 20,750 h in the dark under ambient condition andT80lifetime of 1,050 h at 85 °C and 30% relative humidity. This environmental stability is enabled by the synergetic effect of the stable morphology of donor/acceptor blends and thermally stabilized interfaces due to doping. Furthermore, the high efficiency and good stability are almost 100% retained in ultraflexible OPVs and minimodules which are mechanically robust and have long-term operation capability and thus are promising for future self-powered and wearable electronics.

Intrachain hole delocalization vertical to donor and acceptor interface weakens coulombic interaction of the charge pairs and facilitate the charge separation in organic solar cells.

Slab optical waveguide absorption spectra reveal that surface segregated monolayers of a vertically oriented poly(3-buthylthiophene) derivative have large optical anisotropy, and that confinement of the polymer chains in the isolated monolayer causes strong H-aggregation.

Surface-segregated monolayers (SSMs) based on two poly(3-alkylthiophene)s with semifluoroalkyl groups at either the side chains (P3DDFT) or one end of the main chain (P3BT-F) were used as self-organized buffer layers at the electrode interfaces in bulk heterojunction (BHJ) organic photovoltaic devices. Both of the SSMs greatly shifted the vacuum levels of the BHJ films at the surface due to the aligned permanent dipole moments of the semifluoroalkyl chains. Hole extraction in the BHJ of poly(3-hexylthiophene) (P3HT):[6,6]-phenyl C-butyric acid methyl ester (PCBM) became more efficient in the presence of the P3DDFT buffer layer, resulting in an improved power conversion efficiency. In contrast, the SSM of P3BT-F induced changes in the chain orientation of P3HT and the morphology of the BHJ films, resulting in decreased performance. These results indicate that the molecular design of polymer-based SSMs can affect not only the energy structure at the interface but also the morphology and the molecular orientations in the BHJs.

Semiconducting copolymers based on benzo-[1,2-b:4,5-b′]dithiophene and thieno [3,4-c]pyrole-4,6-dione containing oligo(thienylenevinylene) side chains with different lengths were synthesized to examine the effect of the πconjugated side chains on the performance of polymer solar cells (PSCs). Using the copolymers that had π-conjugated side chains as the PSC electron donor resulted in a higher short circuit current and fill factor compared with the reference copolymers, which had no side chain or an analogous side chain with no π-conjugation, resulting in an increase of power conversion efficiency of 10−22%. Measurements of hole mobility by space-charge-limited current and internal quantum efficiency indicated that introducing the π-conjugated side-chain units can facilitate both charge transport and charge separation in the polymer:PC 71 BM blend films.

Diketopyrrolopyrrole (DPP)-based semiconducting polymers were synthesized with the alkyl side chains of 3,7,11,7,11, that are derived from phytol, a naturally occurring diterpene alcohol. The properties of these polymers were compared to those of DPP-2-octyldodecyl (DPP-OD), a polymer comprising a conventional branched alkyl side chain having the same number of carbon atoms as TMHDe and TMHD. DPP-TMHDe and DPP-TMHD showed good solubility in organic solvents and had longer effective conjugation lengths than DPP-OD in diluted solutions. In thin films, DPP-TMHDe and DPP-TMHD showed higher crystallinity and higher orientational order than those of DPP-OD, resulting in 3−5-fold higher hole mobility in organic field-effect transistors (OFETs). The device performance of OFETs based on DPP-TMHD was characterized by a particularly high thermal stability, up to a temperature of 250 °C, resulting from the robust packing structure of the polymer. Use of these phytol-based solubilizing groups in extended πconjugated molecules can be a useful design strategy to strike a good balance between molecule solubility and relevant thin-film crystallinity.

A poly(3-butylthiophene) derivative with an end group of 1,1,1,3,3,5,5-heptamethyl trisiloxane group (P3BT-Si) was synthesized for the application of surface segregated monolayer (SSM) in polymer films. The surface segregation behaviors, thermal properties and chain orientation of P3BT-Si were investigated. The formation of the surface layer of P3BT-Si was confirmed in the blend films with polystyrene. In contrast to the fluoroalkylterminated polymer (P3BT-F17) that shows strong end-on orientation in the SSM with high crystallinity, P3BT-Si showed edge-on orientation in the SSM with low crystallinity. The difference can be attributed to the more flexible structure of trisiloxane group than the fluoroalkyl chain.

A chiral polythiophene surfactant based on poly­(3-(S)-2-methylbutylthiophene) ((S)-P3MBT) with a semifluoroalkyl group at one end of the main chain was synthesized and used to form surface-segregated monolayers (SSMs). Films of pure (S)-P3MBT mainly adopted the edge-on orientation, whereas (S)-P3MBT films with a SSM of the polymer surfactant (S)-P3MBT-F17 contained a large proportion of end-on-oriented polythiophene, both at the surface and inside the films. The thin films with the SSM showed circular dichroism signals, with the sign opposite to those observed in (S)-P3MBT films. These findings suggest that the orientation-controlled SSM layers induced changes in the packing of the polymer aggregates in the films, resulting in a dramatic change in the excitonic interactions of the chiral semiconducting polymers.