Oligoethylene Glycol Side-Chain Engineering of Y6-Derived Nonfullerene Acceptors for Thermally Induced Spontaneous Pseudo-Planar Heterojunction Organic Photodetectors

Abstract

Dark current density (J D) fundamentally limits the noise characteristics and detectivity of organic photodetectors (OPDs), arising primarily from reverse-bias carrier injection and trap-mediated leakage pathways in donor-acceptor (D-A) bulk-heterojunction (BHJ) active layers. Although pseudo-planar heterojunction (p-PHJ) architectures effectively suppress these losses, their implementation often requires complex layer engineering or controlled processing conditions. Here, we report two Y6-derived nonfullerene acceptors (NFAs), YTEG-4F and YTEG-4Cl, bearing hydrophilic oligoethylene glycol (OEG) side chains that induce thermally driven spontaneous vertical phase separation within the D-A BHJ layer. This molecular modification enables p-PHJ formation, suppressing reverse-bias carrier injection and leakage pathways, thereby reducing J D. In contrast to the thermally annealed PM6:Y6 device, which exhibits an increased J D of 6.64 & times; 10-7 A cm-2, the PM6:YTEG-4F and PM6:YTEG-4Cl devices achieve low J Ds of 2.76 & times; 10-9 and 3.24 & times; 10-9 A cm-2, corresponding to approximately 260-fold and 210-fold reductions after thermal annealing, respectively. Consequently, shot-noise-limited detectivities (D sh*) of 1.17 & times; 1013 and 9.74 & times; 1012 Jones are achieved at -0.5 V for PM6:YTEG-4F and PM6:YTEG-4Cl p-PHJ OPDs, respectively. This work demonstrates that OEG side-chain engineering of NFAs provides a broadly applicable molecular strategy for inducing p-PHJ architectures and regulating J D toward high-performance OPDs.