Design optimization of mutual dissolution layer and diffusion interface layer in planar heterojunction near-infrared organic phototransistors for ultrahigh photosensitivity

Abstract

The interfacial mutual solubility can result in a random distribution of donor and acceptor materials during the spin-coating step in the fabrication of planar heterojunction (PHJ) near-infrared (NIR) organic phototransistors. In this case, deep trap states are induced by acceptors, accelerating electron-hole recombination, ultimately impairing the photoresponsivity of the phototransistor. To solve this issue, a controllable mutual dissolution layer (formed by co-solvent treatment) combined with a diffusion interface layer (formed by the solvent vapor annealing (SVA) method) was introduced to achieve a more ordered arrangement of donors and acceptors, thereby enhancing the electrical performance of PHJ-based NIR phototransistors. Compared with a PDPP3T/PC₆₁BM CF device, a PDPP3T/PC₆₁BM THF : CF (SVA) device in which the PC₆₁BM layer is spin-coated with THF : CF co-solvent and with SVA exhibited a significant performance improvement. The device exhibits a reduction in V_o from 23 V to 4 V, a 5-fold increase in ΔV_th (up to ∼26.0 V), a 30-fold enhancement in photocurrent (ΔI_ph ∼64.6 μA), and a dramatic rise in photosensitivity (I_ph/I_dark) from 205 to 5.6 × 10⁸ (850 nm @ 0.1 mW cm⁻²).