Dual-blade-propeller typed SMDs: π-bridge regulation effect on photovoltaic performance.

• A novel electron-donating building unit "PCz" was synthesized. • A series of 3D "dual-blade-propeller" SMDs were synthesized based on "PCz". • Thecompound PCz(3TDPP) 2 achieved a narrow electrochemical bandgap of only 1.37 eV. • PCz(3TDPP) 2 :PC 71 BM-based device produced a PCE of 5.31 % and a J sc of 18.75 mA cm-2. • These studies provide important references for the development of new PV materials. The recent development of organic photovoltaics provides a promising solution to the challenge of global energy demand. Obviously, the design of novel active layer molecules is crucial. Furthermore, the relationship between photovoltaic performance and molecular structure regulation has become more important and deserves further research. Here, a series of 3D "dual-blade-propeller" small molecule donors (SMDs) were designed and synthesized based on the novel "PCz" and diketopyrrolopyrrole (DPP) units. A detailed study was conducted on the ground state geometry and orbital energy levels of molecules through density functional theory (DFT) calculations. It is worth mentioning that the π-bridge regulation strategy has achieved remarkable results, with the HOMO energy level of thiophene oligomer-bridged compound PCz(3TDPP) 2 reaching -5.05 eV and a narrow bandgap of only 1.37 eV. Considering the basic requirements for solution-processed photovoltaic devices, alkyl chains are introduced into π-bridged thiophene oligomers to improve the solubility and film-forming properties of the materials. The PCz(3TDPP) 2 :PC 71 BM-based device obtained the short-circuit current density (J sc) of 18.75 mA cm-2, which is one of the highest currents in reported thiophene oligomer-bridged SMDs. Both experimental and theoretical studies have revealed the important effects of molecular design and π-bridge regulation strategy on photovoltaic performance. These studies provide important references for the development of new photovoltaic materials with novel configurations. A novel 3D electron-donating building block "PCz" was designed and synthesized based on 2,7-substituted carbazole, and three novel A-D-A typed SMDs were synthesized using diketopyrrole (DPP) as the terminal electron-withdrawing units. The synergistic effect of thiophene-oligomer and DPP leads to the formation of a 3D "dual-blade-propeller" configuration, prolonging molecular conjugation, promoting ICT processes, and effectively controlling excessive aggregation between molecules. Consequently, this unique molecular configuration and strong intermolecular π-π interactions give the conjugated system special photovoltaic properties. By comparing experimental results, the compound PCz(3TDPP) 2 among them has the strongest photon absorption. The PCz(3TDPP) 2 :PC 71 BM-based device produced a PCE of 5.31 % and a J sc of 18.75 mA cm-2, which is one of the highest currents in reported thiophene oligomer-bridged SMDs. These results will guide the molecular design of carbazole derivatives and optimize the molecular structure of SMDs. These studies provide important references for the development of new photovoltaic materials with novel configurations. [Display omitted] [ABSTRACT FROM AUTHOR]