Novel Visible-Light Photodetector Based on Two-Dimensional Confined Electron Donor-Acceptor Co-Assembled Layered Double Hydroxide Ultrathin Films.

Abstract

Photodetectors are a class of critical optoelectronic devices that can transform incident light into a detectable electrical signal. In this work, we develop a novel photodetector based on two-dimensional (2D) confined electron donor–acceptor co-assembled ultrathin films (UTFs). The (PCDTBT@CN-PPV/LDHs)n UTFs are composed of an organic electron donor, poly[N-9′-heptadecanyl-2,7-carbazole-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′-benzothiadiazole)] (PCDTBT), and an acceptor, poly(5-(2-ethylhexyloxy)-2-methoxy-cyanoterephthalylidene) (CN-PPV), within inorganic Mg2Al-layered double hydroxides (LDHs). The UTFs exhibit broad-range visible-light absorption, from 400 to 650 nm, resulting from complementary absorption of PCDTBT and CN-PPV. The fluorescence emission of the UTFs is completely quenched, implying the occurrence of photoinduced charge transfer (PCT). As a novel photodetector, the co-assembled UTFs have a high photocurrent and on/off switching ratio (300 nA/∼120), in contrast to those of the PCDTBT/CN-PPV drop-casting thin film (5.4 nA/∼1.6); a fast response; a short recovery time (lower than 0.1 s); and excellent wavelength and light-intensity dependence. The PCT mechanism can be attributed to the formation of a 2D bulk heterojunction of the two polymers within the interlayers of the LDH nanosheets. Furthermore, flexible UTFs on polyethylene terephthalate substrates are also fabricated, which exhibit excellent folding strength and electrical stability.