Suppressing charge recombination by incorporating 3, 6‐carbazole into poly [9‐(heptadecan‐9‐yl)‐9H‐carbazole‐2, 7‐diyl‐alt‐(5, 6‐bis‐(octyloxy)‐4, 7‐di (thiophen‐2‐yl) benzo [1, 2, 5]‐thiadiazole)‐5, 5‐diyl]