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% (J= 12.37 mA/cm, V = 0.98 V, and fill factor = 0.62), which is much higher than that for a P3HT-MPU1-based device (2.16%) prepared under identical conditions. The higher value for the P-MPU1-based device relative to the P3HT-MPU1-based one is related to the low energy loss and more balanced charge transport in the device based on the P donor. These results indicate that alteration of the absorption spectra and electrochemical energy levels of non-fullerene acceptors, and appropriate selection of the polymer donor with complementary absorption profile, is a promising means to further boost the performance of PSCs.

Devices based on two symmetrical molecules with A–D–A and D–A–D structures and PC71BM show remarkable PCE values of 7.04% and 8.03%.

A bis-porphyrin compound (VC7) has been used as a donor along with two acceptors, namely, PC 71 BM and IT-4F (non-fullerene), for the production of efficient all-small-molecule ternary organic solar cells (OSCs), and their performance has been compared with that of the binary counterparts. After optimization of the ternary blend VC7:PC 71 BM:IT-4F (1:0.3:0.9), organic solar cells showed an overall power conversion efficiency (PCE) of 15.08% (J SC = 23.74 mA/cm 2 , V OC = 0.87 V, and FF = 0.73), which is higher than the values obtained for the binary counterparts, i.e., 9.39 and 11.61% (J SC = 21.94 mA/cm 2 , V OC = 0.84 V, and FF = 0.63) for VC7:PC 71 BM and VC7:IT-4F, respectively. The improvement in the PCE for the ternary OSC is a consequence of the increase in the three parameters, V OC , J SC , and FF. The growth in the V OC value is associated with the upshifted LUMO level of PC 71 BM as compared to IT-4F. The increase in the J SC value is attributed to the higher exciton generation rate, which is associated with the effective utilization of excitons due to the broader absorption profile and energy transfer between the two acceptors (PC 71 BM to IT-4F). The higher FF value of the ternary OSCs is related to the more balanced charge transport and the reduced bimolecular and trap-assisted recombination, as evidenced by the increased charge carrier lifetime and low charge extraction time.

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% (J sc = 13.83 mA/cm2, V oc = 0.91 V, and FF = 0.64) and 8.89% (J sc = 16.98 mA/cm2, V oc = 0.79 V, and FF = 0.663) were obtained, respectively. The high V oc value for the VC4-based OSC correlates with the deeper HOMO, whereas the high J sc 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 recombination, and efficient charge collection. The energy loss for VC5 is smaller (0.52 eV) than that for VC4 (0.56 eV).

Two conjugated acceptor -π-donor -π-acceptor (A-π-D-π-