Difluoro and dicyano substituted sexithiophene − isoindigo terpolymers enabling ternary polymer solar cells with a bulk heterojunction thickness 100 nm → 300 nm and a minor decline of efficiency 14.5 % → 14.0 %

•Both thick (300 nm) and efficient (12.4 % or 14.0 %) ternary polymer solar cells.•Thick ternary polymer solar cells exhibit minor efficiency decline, 0.3 % or 0.5 %•Good shelf lifetime and 1 cm2 of the thick solar cells have been demonstrated.