Synergistic Effects of Selenophene and Extended Ladder-Type Donor Units for Efficient Polymer Solar Cells

Abstract

Two pairs of polymer donor materials based on indacenodithiophene (IDT) and indacenodithieno[3,2-b]thiophene (IDTT) as the donor units are synthesized. Thiophene or selenophene is introduced as the π-bridge units and electron-deficient fluorine-substituted quinoxaline is used as acceptor unit. Selenophene-containing polymers PIDT-DFQ-Se and PIDTT-DFQ-Se show redshifted absorption and narrower bandgaps. Combined with IDTT donor unit, PIDTT-DFQ-Se shows the highest absorption coefficient. Both the IDTT unit and selenophene unit have positive effects on the hole mobilities, making PIDTT-DFQ-Se the highest one. The best power conversion efficiency of 7.4% is obtained from devices based on PIDTT-DFQ-Se:[6,6]-phenyl C₇₁ butyric acid methyl ester (PC₇₁BM) with a J_sc of 12.6 mA cm⁻², a V_oc of 0.89 V, and a fill factor (FF) of 0.66.

Two pairs of electron donor polymer materials with fused-ring indacenodithiophene (IDT) or indacenodithieno[3,2-b]thiophene (IDTT) as donor units bridged with thiophene or selenophene are synthesized. The best power conversion efficiency of 7.4% is obtained from devices fabricated from PIDTT-DFQ-Se:PC₇₁BM due to the synergetic effect of extended IDTT unit and bridged selenophene, resulting in the higher absorption coefficient and mobilities.

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