Direct covalent modification of black phosphorus quantum dots with conjugated polymers for information storage

It has long been recognized that a small switching bias window, which is defined as the difference between the switch-on and switch-off voltages (Δ|VON - VOFF|), and a high ON/OFF current ratio would be greatly favorable to reduce the power consumption of memory devices and to decrease the information misreading rate in digital memory devices. In contrast to two-dimensional BP nanosheets, zero dimensional BP quantum dots (BPQDs) show more exciting physical and chemical properties. By using newly synthesized poly[(9,9-dioctyl-9H-fluorene)-alt-(4-(9H-carbazol-9-yl)aniline)] (PFCz-NH2) as the synthetic precursor, a highly soluble diazotated polymer, PFCz-N2+BF4-, was successfully synthesized and used to react with BPQDs under aqueous conditions to give the first conjugated polymer covalently functionalized BPQDs (PFCz-g-BPQDs). The as-prepared Al/PFCz-g-BPQDs/ITO device exhibits excellent nonvolatile rewritable memory performance, with a large ON/OFF current ratio (>107) and low switch-on/off voltages (-0.89/+1.95 V). In contrast, the Al/PFCz-NH2 : BPQDs blend/ITO device also shows a rewritable memory effect, but its ON/OFF current ratio and Δ|VON - VOFF| value are found to be 3 × 103 and 5.47 (Δ|+2.53-2.94|), respectively. This work, which offers an easy one-step strategy for direct covalent functionalization of BPQDs, opens a way to explore more applications of BPQDs.