D-A copolymers based on lactam acceptor unit and thiophene derivatives for efficient polymer solar cells

Abstract

Two donor-acceptor (D-A) polymers PTTBDTP and PBTBDTP were developed by copolymerizing lactam acceptor [7,7′-bidithieno[3,2-b:2′,3′-d]pyridine]-5,5′(4H,4′H)-dione (BDTP) with thieno[3,2-b]thiophene (TT) or 2,2′-bithiophene (BT) in good yields. PTTBDTP and PBTBDTP exhibited excellent thermal stability and low HOMO energy levels of −5.52 eV ∼ −5.54 eV. Compared with PTTBDTP, PBTBDTP possessed broader absorption spectra, better crystallinity, and higher hole mobility. Therefore inverted polymer solar cells based on PBTBDTP:PC71BM achieved a higher PCE of 6.86%, with an open-circuit voltage (Voc) of 0.87 V, a short-circuit current (Jsc) of 10.97 mA/cm2 and a fill factor (FF) of 71.85%. Meanwhile, PTTBDTP:PC71BM solar cells gave a PCE of 5.84%. These results have demonstrated that lactam BDTP is a good building block for PSC applications.