4 In general, non-fullerene organic acceptors should have broad and strong absorptions in the visible region of the solar spectrum, suitable HOMO/LUMO energy levels, good solubility is common organic solvents and high electron mobility. 3 High power conversion efficiencies (PCEs) in the range of 11–12% have been reported so far for OSCs based on non-fullerene organic acceptors. Non-fullerene organic acceptors have been extensively used during the last couple of years due to their different structures, easier tunability of energy levels, good absorption and ease of synthesis. 1 However, fullerene derivatives have certain drawbacks such as, poor photostability in air, poor solar energy harvesting, high production cost and difficulty in tuning the optical properties over a wide range of energy. In most of the efficient organic solar cells, fullerene derivatives have been extensively used as acceptor materials along with conjugated polymers or small molecules as donors, because of their advantages of high electron mobility and affinity, isotropy of charge transport, and the ability to form favorable nanoscale networks with donor materials. The energy loss ( E loss) of 0.56 eV and 0.48 eV for SM1 and SM2 based devices, respectively is one of the smallest reported for BHJ organic solar cells. The values of V oc of the organic solar cells for the SM1 acceptor (1.06 V and 1.02 V without and with solvent additive) are the highest values reported for devices based on non-fullerene acceptors to the best of our knowledge. The higher value of the PCE for the SM2 based organic solar cells has been attributed to the broader absorption profile, more balanced charge transport and lower photon energy loss. The organic solar cells based on P: SM1 and P: SM2 exhibit a PCE of 4.94% and 6.11%, respectively. These SMs exhibit a broad absorption profile which is complementary to the D–A copolymer P donor and also possess an appropriate lowest unoccupied molecular orbital (LUMO) to serve as an acceptor with P with a LUMO level of –3.33 eV. The electrochemical and optical HOMO–LUMO gaps show similar trends. TCBD and DCNQ linked SM1 and SM2 exhibit multi-redox waves. The energy loss (Eloss) of 0.56 eV and 0.48 eV for SM1 and SM2 based devices, respectively is one of the smallest reported for BHJ organic solar cells.ĭonor–acceptor–acceptor (D–A–A) type 1,8-naphthalimide based small molecules SM1 and SM2 functionalized with tetracyanobutadiene (TCBD) and dicyanoquino-dimethane (DCNQ) modules, showing strong absorption in the visible and near-infrared (NIR) region are reported. The values of Voc of the organic solar cells for the SM1 acceptor (1.06 V and 1.02 V without and with solvent additive) are the highest values reported for devices based on non-fullerene acceptors to the best of our knowledge. The organic solar cells based on P:SM1 and P:SM2 exhibit a PCE of 4.94% and 6.11%, respectively. These SMs exhibit a broad absorption profile which is complementary to the D-A copolymer P donor and also possess an appropriate lowest unoccupied molecular orbital (LUMO) to serve as an acceptor with P with a LUMO level of -3.33 eV. The electrochemical and optical HOMO-LUMO gaps show similar trends. Donor-acceptor-acceptor (D-A-A) type 1,8-naphthalimide based small molecules SM1 and SM2 functionalized with tetracyanobutadiene (TCBD) and dicyanoquino-dimethane (DCNQ) modules, showing strong absorption in the visible and near-infrared (NIR) region are reported.
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