In this study, three novel donor-acceptor (D-A)-type random conjugated terpolymers of PBDTT-PPzBT-H, PBDTT-PPzBT-F and PBDTT-PPzBT-O were synthesized by copolymerizing electron-rich 5,8-dialkylthienyl substituted benzo[1,2-b: 4,5-b']dithiophene (BDTT) and two electron-deficient phenanthro[4,5-abc]phenazine (PPz) and benzo[c][1,2,5]thiadiazole (BT) units. By changing the substituents at the 5,6-positions of BT, the optoelectronic properties of the terpolymers could be rationally adjusted for application as donor materials in polymer solar cells (PSCs). As a result, these terpolymers exhibited different light absorption properties, HOMO energy levels and hole mobilities, which contributed to the optimization of short-circuit current (J(sc)), open-circuit voltage (V-oc) and fill factor (FF) properties, respectively. Interestingly, a maximum power conversion efficiency (PCE) of 6.3% was obtained with an V-oc of 0.75 V, a J(sc) of 13.0 mA cm(-2) and a FF of 64.8% in the PBDTT-PPzBT-O based PSCs using [6,6]-phenyl-C-71-butyric acid methyl ester (PC71BM) as an acceptor, while PBDTT-PPzBT-H and PBDTT-PPzBT-F based devices also demonstrated a PCE of more than 4.5%. To the best of our knowledge, these are the highest recorded maximum PCE, J(sc) and FF values obtained to date compared with previously reported phenazine copolymeric derivatives in BHJ-PSCs. This study illustrates the potential of these random conjugated terpolymers as promising donor materials in the application of PSCs.