A Diarylethene-Based Polymer Additive for Suppressed Dark Current and Enhanced Photo-Response in Organic Photodiodes

The diarylethenes (DAEs), renowned for their reversible photoisomerization, exhibit tunable bandgaps, conductivity, intramolecular or intermolecular radical and energy transfer processes. Leveraging these properties, we designed a DAE based polymer (DEP), and incorporated it as an additive in the photoactive layer of organic photodiodes (OPDs). Radical intermediates of DEP can enhance the photo response of OPDs. With 6 wt.% of DEP in PM6:PC₆₁BM, the suppressed dark current density (J_d) of 1.20 × 10^-9 A cm^-2, increased photocurrent density (J_p) of 9.66 × 10^-4 A cm^-2 and superior detectivity (D*) of 2.02 × 10¹³ Jones are measured at -2 V under 630 nm irradiation, which shows superior performances to its counterpart with J_d of 4.31 × 10^-7 A cm^-2, J_p of 7.02 × 10^-4 A cm^-2, and D* of 8.38 × 10¹¹ Jones without DEP. Mechanistic studies reveal that DEP suppresses dark current by modulating the bandgap and molecular interaction. Meanwhile, the distinct photo response of doped OPDs is attributed to enhanced exciton diffusion and to positive photoconductivity from photoinduced radical intermediates.