Effective Exciton Dissociation and Reduced Charge Recombination in Thick‐Film Organic Solar Cells via Incorporation of Insulating Polypropylene

In organic solar cells (OSCs), the sensitivity of device performance to active layer thickness is a limiting factor for the large‐scale manufacture and roll‐to‐roll production. To reduce the thickness‐dependent effects, a low‐cost insulating polypropylene (PP) material is incorporated into the system with a high crystallinity donor, poly[(2,6‐(4,8‐bis(5‐(2‐ethylhexyl)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))]:[6,6]‐phenyl C71 butyric acid methyl ester (PBDB‐T:PC 71 BM) and the system with a low crystallinity donor, poly[[4,8‐bis[(2ethylhexyl)oxy]‐benzo[1,2‐ b :4,5‐ b ′]dithiophene‐2,6‐diyl][3‐fluoro‐2‐[(2‐ethylhexyl)carbonyl]thieno‐[3,4 b ]thiophenediyl] (PTB7):PC 71 BM. The devices based on PBDB‐T:PC 71 BM:PP (2 wt%) show a power conversion efficiency (PCE) of 7.6% at a thickness of 280 nm compared with the control device with a PCE of 7% at a thickness of 100 nm. The change is mainly due to the enhancement of the crystallinity of donors with high crystallinity. PTB7:PC 71 BM with 4 wt% PP shows higher PCE than the control device for the same thickness (100–300 nm) and reduced PCE with increasing thickness. These are mainly due to the reduced PC 71 BM aggregation. The optimization of crystallinity and morphology will further promote effective exciton dissociation, accelerated charge transport, and reduced charge recombination. It indicates that the low cost and simple method of adding PP is a promising option for roll‐to‐roll production in the future.