Langmuir-Blodgett of Black Phosphorus Thin Films and Photodiodes

Black phosphorus (BP) emerges as a promising optoelectronic material because of its outstanding electrical and optical properties. [ Proc. Natl. Acad. Sci. USA 2015, 112 (15), 4523-30.], Like graphite, BP has a layered structure and can be exfoliated into nanosheets from its bulk form through mechanical and liquid exfoliation. Mechanical exfoliation (the scotch-tape method) has been predominantly used for proof-of-concept devices [Nat. Nanotechnol. 2014, 9 (5), 372-7], but it is inherently unscalable and typically produces BP sheets with lateral size below ten micrometers. For practical applications, scalable approaches for the fabrication of BP large-area films are essential. We will present our results on the development of a Langmuir-Blodgett (LB) protocol which is well suitable for assembling BP nanosheets into thin films. Through functionalization, we achieve large-area (centimeters), homogenous, and smooth BP thin films. With ZnO as an electron transport layer and 1,1-Bis[(di-4-tolylamino) phenyl] cyclohexane (TAPC) as a hole transport layer, the BP films are fabricated into photodiodes, which show responsivity from visible to infrared region. Our work highlights the great potential of BP for applications in near- and mid-infrared detection and imaging.