2.3.2. PFBT2Se2Th:PC71BM OSCs

PFBT2Se2Th:PC71BM devices were fabricated and tested similarly to the description in Section 2.3.1 unless otherwise noted. Six mg mL−<sup>1</sup> PFBT2Se2Th and 12 mg mL−<sup>1</sup> PC71BM were dissolved in DCB with 5 vol % DPE and stirred at 100 ◦C overnight. This solution and ITO/CCO or Mg:CCO substrates were preheated at 100 ◦C. The PFBT2Se2Th:PC71BM active layer (~120 nm thick) was made by first dispensing 50 μL of PFBT2Se2Th:PC71BM solution on the substrate and then immediately starting spinning at 1200 rpm for 60 s, followed by drying in a vacuum chamber for 2 min.

#### 2.3.3. PTB7-Th:ITIC OSCs

PTB7-Th:ITIC devices were fabricated and tested similarly to the description in Section 2.3.1 unless otherwise noted. PTB7-Th and ITIC were blended in a 1:1 weight ratio, dissolved in a mixed solution (CB with 3 vol% CF) at a total concentration of 20 mg mL−<sup>1</sup> and stirred at room temperature overnight. The PTB7-Th:ITIC active layer (~80 nm thick) was made by first dispensing 40 μL PTB7-Th:ITIC solution on the substrate and then immediately starting spinning at 1250 rpm for 60 seconds.
