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Nanocrystal arrays convert light to electrons with 100% ffficiency

Schematic of the nanoparticle array device used to create a high efficiency photo-detector

The conversion of light to electrical current is a key element of many important devices. The sun's energy is harnessed in photovoltaic devices that convert light to electricity in the absence of an applied voltage. Photo-detectors convert light to electricity in the presence of an applied voltage for maximum conversion of photons into detected electrons. MIT MRSEC professors Bawendi and Kastner have found that an array of nanometer size semiconducting particles can behave as remarkably efficient photoconductors (Jarosz et al., Phys. Rev. B 70 , art. no. 195327, 2004). They have demonstrated that, by placing an array of nanoparticles between two gold electrodes (see figure below) and treating the array with a specific molecule, photo-detectors with significantly enhanced efficiency are possible. Three different physics regimes were observed as a function of applied voltage. At low voltage (0-20 volts), light induced excitations in the array largely relax without the creation of any electrical current. At medium voltage (20-70 volts), every excitation is converted to a mobile charge, but that charge is not efficiently extracted from the device. At high voltage (>70 volts) every excitation is converted to a charge that is detected in the external circuit, corresponding to 100% conversion efficiency of absorbed light to an electrical current.

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