The ultraviolet (UV) part in the sunlight is known to cause most damage to organic photovoltaics (OPV). UV filters therefore can improve stability. The lifetime of the UV‐filtered OPV is determined by visible light. Herein, visible sunlight is divided into several bands and modeled by light‐emitting diodes to study the stability of ternary OPV. Poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl‐3‐fluoro)thiophen‐2‐yl)‐benzo[1,2‐b:4,5‐b′]dithiophene))‐alt‐(5,5‐(1′,3′‐di‐2‐thienyl‐5′,7′‐bis(2‐ethylhexyl)benzo[1′,2′‐c:4′,5′‐c′]dithiophene‐4,8‐dione)] (PM6) is used as the donor. 2,2′‐((2Z,2′Z)‐((12,13‐bis(2‐ethylhexyl)‐3,9‐diundecyl‐12,13‐dihydro‐[1,2,5]thiadiazolo[3,4‐e]thieno[2",3″:4′,5′]thieno[2′,3′:4,5]pyrrolo[3,2‐g]thieno[2′,3′:4,5]thieno[3,2‐b]indole‐2,10‐diyl)bis(methanylylidene))bis(5,6‐difluoro‐3‐oxo‐2,3‐dihydro‐1H‐indene‐2,1‐diylidene))dimalononitrile (Y6) is used as the acceptor. Another polymer is added as the second donor to improve the stability. As expected, the deep and light blue bands dominate the decay under visible light. After about 1200 h of blue irradiation, the devices enter a relatively stable state up to 3000 h of tracking, in sharp contrast to the continuous decay under UV. No chemical reaction is observed under blue light. Years of outdoor lifetime for nonfullerene OPV are projected with the UV filter.
