Unveiling the Structural Origin of Low-Frequency Noise in Organic Photodetectors

Active-layer morphology critically shapes the low-frequency noise characteristics of organic photodetectors (OPDs), yet the mechanistic link between crystallization pathway and power spectral density (PSD) remains underexplored. This study demonstrates that solvent evaporation kinetics governs a crystallization sequence that determines low-frequency noise in PM6:Y6 ternary OPDs. Differential scanning calorimetry and surface-energy measurements show that L8-BO has an approximately 41% lower nucleation barrier than Y6, a thermodynamic hierarchy that places L8-BO as the preferentially nucleating component and directs fast-drying chloroform (CF) processing toward a seeded alloy formation route. This nucleation-seeded pathway produces a structurally uniform alloy-like acceptor phase with suppressed energetic disorder (17.9 meV) and low trap density (2.54 × 1012 cm-3). In contrast, slow-drying chlorobenzene (CB) promotes competitive dual-phase crystallization, increases trap density to approximately 4.98 × 1013 cm-3, and drives dark-current activation energy well below Eg/2, indicating shunt-like interfacial leakage. Lorentzian generation-recombination (G-R) noise analysis shows that the G-R roll-off frequency increases monotonically with reverse bias in CF-processed OPDs, consistent with Poole-Frenkel-enhanced Shockley-Read-Hall (SRH) emission from well-localized midgap traps. This trap-kinetics-resolved PSD analysis establishes crystallization pathway engineering as a physically grounded strategy for noise-aware OPD design.