Samsung Advanced Institute of Technology

The series of donor-acceptor (D-A) type random copolymers were designed and synthesized as polymeric acceptors for all-polymer based photodiodes (all-PPDs). These copolymers employ diketopyrrolopyrrole (DPP) as the electron-withdrawing unit and benzodithiophene (BDT) as the electron-donating unit. To introduce structural variation and modulation of their properties, three different π-conjugation spacers, thiophene (T for P1), thienothiophene (TT for P2), and bithiophene (BT for P3), were incorporated into the copolymer structures. These different π-conjugation spacers allow control over electrical and optoelectronic characteristics of the copolymers. This includes the absorption profile, which determines the wavelengths of light that the copolymers can absorb, and the energy levels, such as the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) levels, which influence the charge transport and optoelectronic properties. Additionally, the molecular packing and film morphology of the copolymers can be modulated by varying the π-conjugation spacers. These factors affect the efficiency of charge transport, and overall device performance in all-PPDs. Accordingly, all-PPDs based on the series of P1-P3 as polymer donors (P_Ds) exhibited totally distinct device performances in terms of external quantum efficiency (EQE), dark current density (J_D) and ideal detectivity (D*).