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Two D–A–D small molecules with a DPP acceptor core and Zn-porphyrin donor with different electron-donating substituents, namely, 2,6-bis(dodecyloxy)phenyl and 5-hexylthieno[3,2-b]thiophen-2-yl at mesopositions, VC4 and VC5, were synthesized, and their optical and electrochemical properties were investigated. The results reveal that both molecules are suitable as donors for organic solar cells (OSCs) in which PC71BM is employed as the acceptor. Overall power conversion efficiencies of 8.05% (Jsc = 13.83 mA/cm2, Voc = 0.91 V, and FF = 0.64) and 8.89% (Jsc = 16.98 mA/cm2, Voc = 0.79 V, and FF = 0.663) were obtained, respectively. The high Voc value for the VC4-based OSC correlates with the deeper HOMO, whereas the high Jsc value for VC5 may be attributed to the extended absorption spectrum toward the longer wavelength region. Moreover, the relatively high FF value for VC5-based OSCs as compared to the VC4 counterparts may be related to the more balanced charge transport in the active layer, reduced charge re...

A new D–π–A–π–D small molecule (VC7) based on a selenophene-flanked diketopyrrolopyrrole core and two Zn-porphyrin peripheral moieties was designed and synthesized. The optical and electrochemical properties of VC7 were investigated and compared with those of VC6, which has the same chemical structure but with thiophene units in the π-bridge rather than selenophene. VC7 exhibited extended absorption spectra in the near infrared region of the solar spectrum and showed improved hole mobility with a high HOMO energy level. After optimization of the active layers, VC7:PC71BM organic solar cells (OSCs) showed a significantly higher power conversion efficiency of 9.24% (JSC = 15.98 mA cm−2, VOC = 0.89 V and FF = 0.66) in comparison to VC6:PC71BM (PCE of 7.27%, JSC = 14.31 mA cm−2, VOC = 0.82 V and FF = 0.62); this result represents a 27% increase in efficiency. Our results show that the higher JSC value for the VC7-based OSC is due to a combination of the more extended absorption profile, higher hole mobility, more balanced charge transport and high exciton dissociation probability.

The effect of central donor core on the properties of A-π-D-π-A donors, where D is a porphyrin macrocycle, cyclopenta[2,1-b:3,4-b']dithiophene is the π bridge, and A is a dicyanorhodanine terminal unit, was investigated for the fabrication of the organic solar cells (OSCs), along [6,6]-phenyl-C71-butyric acid methyl ester (PC71 BM) as electron acceptor. A new molecule consisting of Ni-porphyrin central donor core (VC9) showed deep HOMO energy level and OSCs based on optimized VC9:PC71 BM realized overall power conversion efficiency (PCE) of 10.66 % [short-circuit current density (JSC )=15.48 mA/cm2 , fill factor (FF)=0.65] with high open circuit voltage (VOC ) of 1.06 V and very low energy loss of 0.49 eV, whereas the Zn-porphyrin analogue VC8:PC71 BM showed PCE of 9.69 % with VOC of 0.89 V, JSC of 16.25 mA/cm2 and FF of 0.67. Although the OSCs based on VC8 showed higher JSC in comparison to VC9, originating from the broader absorption profile of VC8 that led to more exciton generation, the higher value of PCE of VC9 is owing to the higher VOC and reduced energy loss.

The synthesis of two symmetrical molecules with A–D–A (1) and D–A–D (2) structures is reported. The compounds have Zn-porphyrin as the donor component and 3,6-di(thiophen-2-yl)pyrrolo[3,4-c]pyrrole-1,4-dione (DT-DPP) as the acceptor unit, linked through ethynyl π-bridges. The effect of scaffold modification on the electrochemical, optical and photovoltaic characteristics has been investigated and favourable properties are found for the D–A–D system compared to the A–D–A. These two Zn-porphyrin-based small molecules are used as donors along with PC71BM as the acceptor for the fabrication of solution processed bulk heterojunction organic solar cells in order to obtain information about the effect of donor and acceptor positions on the photovoltaic response of the devices. A strategy for optimizing the morphology of the active layer using a binary solvent additive has been used. After the optimization of the weight ratios between 1 or 2 and PC71BM and the solvent additives, the devices based on 1 : PC71BM and 2 : PC71BM active layers show remarkable PCE values of 7.04% and 8.03%, respectively. The higher PCE obtained for 2 : PC71BM compared to 1 : PC71BM can be related to the increase in Jsc and FF and attributed to lower energy loss, strong π–π intermolecular stacking and more balanced charge transport.

Herein we report the synthesis of a novel A-D-A-D-A non-fullerene small-molecule acceptor (NFSMA) bearing a diketopyrrolopyrrole (DPP) acceptor central core coupled to terminal rhodanine acceptors via a thiophene donor linker (denoted as MPU1) for use in non-fullerene polymer solar cells (PSCs). This NFSMA exhibits a narrow optical band gap (1.48 eV), strong absorption in the 600–800 nm wavelength region of the solar spectrum, and a lowest unoccupied energy level of −3.99 eV. When the mixture of a medium band gap D–A copolymer P (1.75 eV) was used as donor and MPU1 as acceptor, the blend film showed a broad absorption profile from 400 to 850 nm, beneficial for light harvesting efficiency of the resulted polymer solar cell. After optimization of the donor-to-acceptor weight ratios and concentration of solvent additive, the P–MPU1-based PSC exhibited a power conversion efficiency of 7.52% (Jsc= 12.37 mA/cm2, Voc = 0.98 V, and fill factor = 0.62), which is much higher than that for a P3HT–MPU1-based device (...

A single isomer of a pyrazolinofullerene bis-adduct was prepared by tether-directed remote functionalization. Specifically, a macrocyclization reaction between C60 and a bis-hydrazone reagent has been carried out to generate a regioisomerically pure fullerene bis-adduct which presents a lower LUMO than pristine C60.

Two conjugated acceptor–p–donor–p–acceptor (A–p–D–p–A) small molecules with a zinc porphyrin donor core and 3-ethylrhodanine terminal acceptors connected at the meso positions by ethynylene groups and linked by one or two thienylenevinylene units denoted by 1a and 1b were synthesized and their optical and electrochemical properties were investigated. Bulk heterojunction organic solar cells fabricated with 1a : PC71BM and 1b : PC71BM processed with THF exhibited power conversion efficiencies of 2.75% (Jsc ¼ 7.96 mA cm_x0002_2, Voc ¼ 0.96 V and FF ¼ 0.36) and 3.18% (Jsc ¼ 8.84 mA cm_x0002_2, Voc ¼ 0.90 V and FF ¼ 0.40), respectively. Moreover, organic solar cells based on 1a : PC71BM and 1b : PC71BM processed with pyridine/THF solution displayed PCEs of 5.27% (Jsc ¼ 10.61 mA cm_x0002_2, Voc ¼ 0.92 V and FF ¼ 0.54) and 5.78% (Jsc ¼ 11.58 mA cm_x0002_2, Voc ¼ 0.86 V and FF ¼ 0.58), respectively. However, most important is the observation that the PCE was further increased to 7.24% for devices based on 1a : PC71BM and 1b : PC71BM active layers processed with pyridine/THF solution by employing CuSCN as a selective contact electrode instead of the most common hole transport material, namely, PEDOT:PSS.