•BHJ OPVs based on PEDOTNDIF and neat C70 or PC70BM were fabricated.•BHJ OPVs using PC70BM exhibited a PCE of 0.30%.•BHJ OPVs using neat C70 exhibited a PCE of 2.33%.•The much-improved PCE is mainly due to a strong acceptor nature of neat C70.Low-cost neat C70 was successfully utilized to fabricate solution-processable bulk heterojunction (BHJ) organic photovoltaics (OPVs) by combining the neat C70 with an amorphous polymer, PEDOTNDIF, which was also synthesized at low cost by using a two-step direct arylation reaction. The optimized BHJ OPV using PEDOTNDIF:C70 exhibited a short-circuit current density (Jsc) of 8.70 mA cm−2, an open-circuit voltage of 0.75 V, a fill factor of 0.36, and a power conversion efficiency (PCE) of 2.33%, as compared to 1.46 mA cm−2, 0.80 V, 0.26, and 0.30%, respectively, for the BHJ OPV fabricated using PEDOTNDIF:PC70BM. The much-improved PCE (Jsc) is mainly due to the strong acceptor nature of neat C70, which needs to efficiently separate photo-excitons into free carriers. A good miscibility in the PEDOTNDIF:C70-based BHJ film with a large donor/acceptor interfacial area was also confirmed by characterizing atomic force microscopy images of the BHJ films and comparing PCEs of planar-heterojunction OPVs with PEDOTNDIF/C70 bilayers.

•The synthesis of the amorphous D-A polymer, poly(NTD-TPA), is reported.•Poly(NTD-TPA) had an absorption edge at longer wavelengths than poly(CR-TPA).•BHJ OPVs based on poly(NTD-TPA) exhibited a PCE of 2.15%.We report the synthesis and photovoltaic properties of a donor–acceptor polymer, poly(naphthobisthiadiazole-triphenylamine) [poly(NTD-TPA)], which consists of TPA as a donor unit and NTD as a stronger acceptor than benzothiadiazole. This polymer had an absorption edge at wavelengths up to 610 nm. The optimized bulk-heterojunction (BHJ) organic photovoltaic (OPV) cell using poly(NTD-TPA) and [6,6]-phenyl C71 butyric acid methyl ester (PC70BM) exhibited a short-circuit current of 6.87 mA cm−2, an open-circuit voltage Voc of 0.79 V, a fill factor of 0.40, and a power conversion efficiency of 2.15%. The validities of these photovoltaic properties are discussed using the incident-photon-to-current conversion efficiency, film morphology, field-effect hole mobility, and electroluminescence (EL) spectrum from the charge transfer states between the highest occupied molecular orbital of poly(NTD-TPA) and the lowest unoccupied molecular orbital of PC70BM. In particular, the Voc estimated from the current density–voltage curve agreed well with that estimated from the peak energy of the EL spectra.

A comparative study of the properties of bulk-heterojunction organic photovoltaic cells (OPVs) using a benzothiadiazole (BTD)–triphenylamine (TPA) small molecule and its polymerized molecule (poly(BTD-TPA)) is presented. OPVs using BTD-TPA or poly(BTD-TPA):PC60BM at a 1:2 mixing weight ratio were fabricated. The power conversion efficiency (PCE) of the poly(BTD-TPA)-based OPV was twice that of the BTD–TPA-based OPV. The field-effect hole mobility of poly(BTD-TPA) is two orders of magnitude higher than that of BTD–TPA and the absorption peak of poly(BTD-TPA) is at a longer wavelength than that of BTD–TPA. Accordingly, the improved hole mobility and enhanced absorption of AM1.5 solar-simulated light led to a high short-circuit current (Jsc) and PCE in OPVs based on poly(BTD-TPA). Using OPVs with poly(BTD-TPA):PC70BM (1:4), the device performance exhibited a Jsc value of 7.45 mA cm−2, an open-circuit voltage of 0.92 V, a PCE of 2.65%, and incident photon to current conversion efficiencies of around 50% at wavelengths ranging from 360 to 560 nm. The experimental results for the OPVs with BTD–TPA-based materials indicate that the polymer is effective for obtaining high-performance OPVs.

An amorphous polymer, poly(BTD-TPA), which consists of benzothiadiazole and triarylamine units, can be successfully utilized to fabricate bulk heterojunction (BHJ) organic photovoltaics (OPVs), and the OPV performance can be demonstrated to be independent of the casting solvent or thermal annealing temperature. The OPV based on poly(BTD-TPA):PC70BM (1:4) that was fabricated using chloroform (boiling point of 61 °C) and annealed at 60 °C for 10 min exhibited a power conversion efficiency (PCE) of 2.81% under simulated solar irradiation through an air mass of 1.5 at 100 mW cm−2. On the other hand, the OPV fabricated using o-dichlorobenzene (boiling point of 181 °C) and annealed at 110 °C for 10 min exhibited a PCE of 2.65%. Almost the same PCEs and incident photon to current conversion efficiencies (IPCEs) were obtained in both OPVs. The use of an amorphous film of poly(BTD-TPA) in the fabrication of OPVs offers great advantages over the use of a polycrystalline film of regioregular poly(3-hexylthiophene) (P3HT) in terms of high reproducibility of the OPV performance.Graphical abstractHighlights► BHJ OPVs based on an amorphous polymer, poly(BTD-TPA), were fabricated. ► OPV performance was independent of the casting solvent and the thermal annealing temperature. ► OPVs exhibited a PCE of 2.81%. ► Use of poly(BTD-TPA) offers advantages in terms of high reproducibility of the OPV performance.

We synthesized naphthyl end-capped divinylbenzenes, in which naphthyl replaces phenyl as the substituent at the terminal positions of the oligo-p-phenylenevinylenes, and investigated the performance of organic field-effect transistors (OFETs), air stability and molecular packing in poly- and single-crystalline films. The OFETs exhibited field-effect hole mobility up to 0.21 cm2 V−1 s−1 when the organic semiconductor was evaporated on substrate at 90 °C. Field-effect mobility in air at a controlled temperature of 30 °C and high humidity of 80% was almost constant for a period of up to 220 days, indicating that the material is a very stable organic semiconductor in air.

A comparative study of the properties of bulk-heterojunction organic photovoltaic cells (OPVs) using a benzothiadiazole (BTD)–triphenylamine (TPA) small molecule and its polymerized molecule (poly(BTD-TPA)) is presented. OPVs using BTD-TPA or poly(BTD-TPA):PC60BM at a 1:2 mixing weight ratio were fabricated. The power conversion efficiency (PCE) of the poly(BTD-TPA)-based OPV was twice that of the BTD–TPA-based OPV. The field-effect hole mobility of poly(BTD-TPA) is two orders of magnitude higher than that of BTD–TPA and the absorption peak of poly(BTD-TPA) is at a longer wavelength than that of BTD–TPA. Accordingly, the improved hole mobility and enhanced absorption of AM1.5 solar-simulated light led to a high short-circuit current (Jsc) and PCE in OPVs based on poly(BTD-TPA). Using OPVs with poly(BTD-TPA):PC70BM (1:4), the device performance exhibited a Jsc value of 7.45 mA cm−2, an open-circuit voltage of 0.92 V, a PCE of 2.65%, and incident photon to current conversion efficiencies of around 50% at wavelengths ranging from 360 to 560 nm. The experimental results for the OPVs with BTD–TPA-based materials indicate that the polymer is effective for obtaining high-performance OPVs.