Towards all‐solution‐processed top‐illuminated flexible organic solar cells using ultrathin Ag‐modified graphite‐coated poly(ethylene terephthalate) substrates

All‐solution‐processed flexible organic solar cells (FOSCs) with high power conversion efficiency (PCE) are the prerequisite for application in low‐cost, large‐area, flexible, photovoltaic devices. In this work, high‐performance, top‐illuminated FOSCs using ultrathin Ag‐modified graphite‐coated poly(ethylene terephthalate) (PET) substrates are demonstrated. The ultrathin Ag‐modified graphite/PET substrates have excellent electric conductivity, mechanical flexibility, and easy processability for FOSCs. A PCE of 5.31% for FOSCs, based on the blend system poly[4,8‐bis(5‐(2‐ethylhexyl)thiophen‐2‐yl)benzo [1,2‐b:4,5‐b′]dith‐iophene‐ co ‐3‐fluorothieno[3,4‐b]thiophene‐2‐carboxylate]: [6,6]‐phenyl‐C7l‐but‐yric acid methyl ester, having a bilayer of MoO x /Ag upper transparent anode is demonstrated. Top‐illuminated FOSCs with a transparent upper electrode of solution‐processed Ag nanowires also yielded a PCE of 3.76%. All‐solution‐processed FOSCs exhibit excellent mechanical flexibility and retain >81% of the initial efficiency after 500 cycles of bending test. Furthermore, graphite‐based electrodes demonstrate good heat‐insulation properties. The outcomes of this work offer an alternative to fabricate high‐performance, all‐solution‐processable, top‐illuminated FOSCs, providing a commercially viable approach for application in large‐area solar cells that can be prepared by printing and roll‐to‐roll fabrication processes.