We studied fullerene-free organic solar cells based on electron-donating (BDT3TR) and -accepting (O-IDTBR) small molecules. Bulk heterojunction devices comprising BDT3TR:O-IDTBR showed an excellent power conversion efficiency exceeding 7% and much better thermal stability than BDT3TR:PC₇₀BM devices after ageing at 120 °C for 300 hours.