Synthesis of triarylamine-based alternating copolymers for polymeric solar cell

Two donor-acceptor alternating copolymers based on electron-rich triarylamine, di(1-(6-(2-ethylhexyl))naphthyl)phenylamine (DNPA), and electron-deficient benzothiadiazole and benzoselenadiazole derivatives were designed and synthesized via Suzuki coupling reaction. The resulting triarylamine-based alternating copolymers PDNPADTBT and PDNPADTBS showed good solubility in common organic solvents and good thermal stability. The optical band gaps determined from the onset absorption were 1.93 and 1.81 eV, respectively. By introducing the naphthalene ring into the triarylamine, copolymers had relatively deep HOMO energy levels of -5.48 and -5.45 eV, which led to a high open circuit voltage (V_oc) and good air stability for photovoltaic application. Bulk heterojunction solar cells were fabricated with a structure of ITO/PEDOT-PSS/copolymers-PC₇₀BM/LiF/Al by blending the copolymer with PC₇₀BM. Both blend systems showed remarkably high V_oc near 0.9 V, and the highest performance of 2.2% was obtained from PDNPADTBT, with V_oc = 0.88 V, J_sc = 7.4 mA/cm², and a fill factor of 34.4% under AM 1.5 G.