Highly ordered bimolecular crystalline blends for low-noise and high-detectivity polymeric photodiodes

Abstract

Suppressing noise current while maintaining high quantum efficiency is essential for realizing high-performance photodiodes. Solution-processed polymeric photodiodes, however, often suffer from high noise current levels because of undesired charge injection in the reverse saturation regime or localized energy states, resulting from the presence of structural imperfection. In this study, we demonstrated that such structural disorder can be avoided by constructing active layers with bimolecular crystallites. X-ray analyses of poly(2,5-bis(3-tetradecyllthiophene-2-yl)thieno[3,2-b]thiophene):phenyl-C61-butyric acid methyl ester blends confirmed low paracrystalline disorder and a high degree of orientation ordering of the active layers. The resulting optimized photodiodes with 80% PCBM content showed a high detectivity value of 1.95 × 10¹² Jones, a high bandwidth of 1 kHz, and a high 94 dB linear dynamic range. This result implies that optimizing the structural perfectness of the active layers can be a decisive factor for low noise current and thus high detectivity of the solution-processed polymeric photodiodes.