Fig. 1. (a) Chemical structures of PC₇₁BM、O-IDTBR and their energy level diagrams; (b) Current density-Voltage curves of the PC₇₁BM and O-IDTBR based devices.

Fig. 2. (a) V_oc-Temperature curves of the devices using different electron acceptors; (b) Mott- Schottky curves for the devices.

Fig. 3. (a) Recombination resistance as a function of the light intensities, inset: Equivalent circuit of the measured impedance spectrum; (b) transient photovoltage curves of the devices.

Fig. 4. Electroluminescence of the (a) PC₇₁BM and (b) O-IDTBR based devices with various injection current.

Fig. 5. (a) Illustration of the fluorescence emission process in the polymer solar cells; (b) illustration of the impact of energy disorder on the open-circuit voltage.