NIR polymers and phototransistors

A novel bisthiophene-fused diketopyrrolopyrrole unit (4,11-bis(2-octyldodecyl)-7 H ,14 H -thieno[3′,2′:7,8]indolizino[2,1- a ]thieno[3,2- g ]indolizine-7,14-dione, BTI) has been designed as an electron acceptor and used to copolymerize with thiophene and bithiophene as electron donors to construct two D-A conjugated polymers, P1 and P2 via Stille coupling, respectively. The two polymers showed excellent thermal stability, broad light absorption and a narrow energy band gap. P1 and P2 were used to fabricate organic field-effect transistors (OFETs) to evaluate their charge transport characteristics. P2 showed much better hole transport performance with a mobility of 0.1 cm 2 V −1 s −1 . Near-infrared (NIR) phototransistors were also fabricated by using the two polymers blended with PC 71 BM as the active layer. With illumination of 35 μW cm −2 at a wavelength of 850 nm, the photocurrent/dark-current ratio ( P ) and photoresponsivity ( R ) of the phototransistor based on P1 /PC 71 BM were 3.6 × 10 4 and 270 A W −1 , respectively. For P2 /PC 71 BM, P was 2.5 × 10 4 and R reached 2420 A W −1 . A novel bisthiophene-fused diketopyrrolopyrrole unit (4,11-bis(2-octyldodecyl)-7 H ,14 H -thieno[3′,2′:7,8]indolizino[2,1- a ]thieno[3,2- g ]indolizine-7,14-dione, BTI) has been designed as an electron acceptor and used to copolymerize with thiophene and bithiophene as electron donors to construct two D-A conjugated polymers, P1 and P2 via Stille coupling, respectively.