文摘
To gain ideal conjugated polymers with a low band-gap (Eg) and a deep HOMO (highest occupied molecular orbital) energy level for photovoltaic application, both strong and weak electron withdrawing units were introduced into polymer backbone. A series of -(D-A1-D-A2)n- type diketopyrrolopyrrole (DPP) containing polymers P1-P7 were designed and synthesized. The resulting copolymers exhibited both low Eg of 1.27-1.48?eV and deep HOMO energy levels of ?5.25to ?5.44?eV. Preliminary photovoltaic properties of the copolymers blended with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) were investigated. All photovoltaic devices featured high open circuit voltages (Voc, 0.72-0.91?V). Among the seven copolymers, P5 exhibited the best performance with a Voc of 0.80?V, a short circuit current density (Isc) of 3.48?mA/cm2, a fill factor (FF) of 43.2 % , and a power conversion efficiency (PCE) of 1.33 % .