Solution-processed PbS quantum dot infrared photodetectors and photovoltaics

Abstract

In contrast to traditional semiconductors, conjugated polymers provide ease of processing, low cost, physical fl exibility and large area coverage1. Th ese active optoelectronic materials produce and harvest light effi ciently in the visible spectrum. Th e same functions are required in the infrared for telecommunications (1,300-1,600 nm), thermal imaging (1,500 nm and beyond), biological imaging (transparent tissue windows at 800 nm and 1,100 nm), thermal photovoltaics (>1,900 nm), and solar cells (800-2,000 nm). Photoconductive polymer devices have yet to demonstrate sensitivity beyond ∼800 nm (refs 2,3). Sensitizing conjugated polymers with infrared-active nanocrystal quantum dots provides a spectrally tunable means of accessing the infrared while maintaining the advantageous properties of polymers. Here we use such a nanocomposite approach in which PbS nanocrystals tuned by the quantum size eff ect sensitize the conjugated polymer poly[2-methoxy-5-(2′-ethylhexyloxy-pphenylenevinylene)] (MEH-PPV) into the infrared. We achieve, in a solution-processed device and with sensitivity far beyond 800 nm, harvesting of infrared-photogenerated carriers and the demonstration of an infrared photovoltaic eff ect. We also make use of the wavelength tunability aff orded by the nanocrystals to show photocurrent spectra tailored to three diff erent regions of the infrared spectrum.