Synthesis and characterization of a pentaselenophene-based donor-acceptor copolymer for use in organic photovoltaic cells

A new conjugated polymer containing pentaselenophene (5Se) electron donor moieties was designed for use in polymer solar cells and synthesized via a Stille coupling reaction. The structure, optical properties, electrochemical properties, hole mobility, photovoltaic properties, and AFM morphology of the homopolymer (P5Se) and the donor-acceptor copolymer (P5SeDTDPP) with a diketopyrrolopyrrole (DPP) acceptor were investigated and are discussed. The polymers showed good solubility, film-forming properties, and thermal stabilities. P5Se exhibited a broad absorption across the visible range, 400-700 nm, which is a prerequisite for photovoltaic applications. P5SeDTDPP yielded a broader absorption spectrum, enhanced π-π interactions, and a lower band gap compared to P5Se, due to the enhanced intramolecular charge transfer interactions between the donating moiety (pentaselenophene) and the DPP accepting moiety. Solution-processed field effect transistors fabricated from these polymers displayed p-type organic thin film transistor characteristics. P5Se and P5SeDTDPP exhibited typical p-type organic semiconductor characteristics with hole mobilities of 2.3×10^-3 and 1.2×10^-2 cm² V^-1 s^-1, respectively. Photovoltaic devices were fabricated using polymer:PCBM blends in ITO/PEDOT:PSS/blend/Al structures. The P5SeDTDPP device exhibited an open circuit voltage (V_OC) of 0.44 V, a short circuit current (J _SC) of 10.67 mA/cm², a fill factor (FF) of 0.51, and a power conversion efficiency (PCE) of 2.40% under AM 1.5 G (100 mW/cm ²) conditions.