Design of ternary additive for organic photovoltaics: a cautionary tale.

Silicon phthalocyanines as ternary additives are a promising way to increase the performance of organic photovoltaics. The miscibility of the additive and the donor polymer plays a significant role in the enhancement of the device performance, therefore, ternary additives can be designed to better interact with the conjugated polymer. We synthesized N -9'-heptadecanyl-2,7-carbazole functionalized SiPc ((CBzPho) 2 -SiPc), a ternary additive with increased miscibility in poly[ N -90-heptadecanyl-2,7-carbazole-alt-5,5-(4',7'-di-2-thienyl-2',1',3'-benzothiadiazole)] (PCDTBT). The resulting additive was included into PCDTBT and [6,6]-phenyl C 71 butyric acid methyl ester as bulk (PC 71 BM) heterojunction OPV devices as a ternary additive. While the (CBzPho) 2 -SiPc demonstrated strong EQE >30% contribution in the range of 650-730 nm, the overall performance was reduced because (CBzPho) 2 -SiPc acted as a hole trap due to its high-lying HOMO energy level. This study demonstrates the importance of the solubility, miscibility, and energy level engineering of the ternary additive when designing organic photovoltaic devices.