Green Dioxythiophene-Benzothiadiazole Donor−Acceptor Copolymers for Photovoltaic Device Applications

With the perspective of producing power-generating displays of various colors based on π-conjugated semiconducting polymers, we have developed a synthetic design aimed at addressing color states commonly difficult to attain. Herein, we report on the structure−property relationships and performance in photovoltaic devices of a series of green-colored donor−acceptor (DA) π-conjugated polymers comprised of electron-rich 3,4-dioxythiophenes (DOTs) and the electron-deficient 2,1,3-benzothiadiazole (BTD). In particular, the synthesis and chemical polymerization of two DOT-BTD regiosymmetric oligomers (pentamers M2 and M3 ), that can be chemically oxidized to yield two-band absorbing polymers with a transmission window in the 480−560 nm range hence reflecting/transmitting the color green ( P2 and P3 ), is reported. The optical and electrochemical properties of P2 and P3 are described and compared to those of a blue-colored parent polymer ( P1 ) obtained via the polymerization of a smaller DOT-BTD oligomeric precursor (trimer M1 ). The photovoltaic (PV) properties of P1 − P3 were investigated in DA bulk heterojunction (BHJ) devices with PC 60 BM as the acceptor. P2 and P3 afforded green-colored devices with up to 1.9% power conversion efficiency (PCE) under AM 1.5 G solar illumination. Taking into account the differences in polymer energy band structure, we have replaced PEDOT:PSS by MoO 3 and optimized the solar-cell device configuration for the most efficient polymer derivative ( P3 ), demonstrating up to a 2.71% PCE. Insight into the morphology and charge transport of these polymers in blends with PCBM is provided and related to the synthetic design and PV device performance.