Highly efficient layer-by-layer deposition solar cells achieved with halogen-free solvents and molecular engineering of non-fullerene acceptors

Finely Tuned Molecular Packing Realized by a New Rhodanine-Based Acceptor Enabling Excellent Additive-Free Small- and Large-Area Organic Photovoltaic Devices Approaching 19 and 12.20% Efficiencies

“…UV–vis absorption of the neat film exhibits a red-shift (40 nm) and vibration shoulder peaks in comparison to the solution state. This shows that there are strong intermolecular π–π interactions and good film aggregation in the film absorption. ,, Therefore, the absorption onset of BTA-ERh is located at 735 nm with an optical band gap ( E g opt ) of 1.68 eV. The absorption spectra of the pristine films PM6, Y7, and PC 71 BM are shown in Figure b.…”

“…More importantly, the BTA unit has strong electron-donating abilities (presence of the N atom), which reduces the optical bandgap (improving ICT) and suppresses charge recombination, enhancing PCEs and the stability of OSCs owing to the absence of the S atom . For example, recently, we reported 17.55% PCE for a green-solvent process, and the side chains on the thienothiophene and BTA moieties in the NFAs were investigated . In 2022, Li et al reported a BTA moiety core building block and thiophene end group and achieved a good short-circuit current density ( J sc ) (25.05 mA/cm 2 ) and a PCE of 16.58% in ternary OSCs .…”

“…By using energy-dispersive X-ray spectroscopy (EDS) mapping and FE-SEM, the molecular behavior of the optimized blend devices was examined. , EDS mapping was used to determine the polymer and acceptor distributions. Figure S12 displays the images of the Cl, S, O, and F atomic signals that were obtained.…”

“…The effect of BTA-ERh on the charge transfer capacity was investigated using electrochemical impedance spectroscopy (EIS), which was carried out in dark conditions. ,, The sheet resistance ( R sheet ) of the electrodes and the charge transport resistance ( R CT ) associated to the active layer/electrode interfaces and active layers make up the series resistance ( R s ), as illustrated in the added model in Figure S15. The R CT values of the PM6:Y7:PC 71 BM and PM6:Y7:PC 71 BM:BTA-ERh devices were 288 and 22 kΩ cm 2 , respectively, as shown in Figure S15.…”

“…Additionally, adding a longer side chain to the dithiophene unit improves the mobility values and PCEs while increasing the blend’s solubility without excessive aggregation. Especially, “Y-series” of NFAs (Y1 to Y7) exhibits a broadened absorption range, boosts the ICT property, provides positive charge transport due to stacking (π–π) in molecules, and improves the PCEs for efficient OSCs. ,− Li et al introduced an NFA, Y18, by substituting a BTA unit on the central core with a benzothiadiazole unit in Y6, which showed good optical absorption and up-shifted molecular energy levels compared to Y6 (control acceptor) . The Y18-based binary device realized a PCE of 16.52%.…”