Coaxial silicon nanowires as solar cells and nanoelectronic power sources

Solar cells are attractive candidates for clean and renewable power(1,2); with miniaturization, they might also serve as integrated power sources for nanoelectronic systems. The use of nanostructures or nanostructured materials represents a general approach to reduce both cost and size and to improve efficiency in photovoltaics(1-9). Nanoparticles, nanorods and nanowires have been used to improve charge collection efficiency in polymer-blend(4) and dye-sensitized solar cells(5,6), to demonstrate carrier multiplication(7), and to enable low-temperature processing of photovoltaic devices(3-6). Moreover, recent theoretical studies have indicated that coaxial nanowire structures could improve carrier collection and overall efficiency with respect to single-crystal bulk semiconductors of the same materials(8,9). However, solar cells based on hybrid nanoarchitectures suffer from relatively low efficiencies and poor stabilities(1). In addition, previous studies have not yet addressed their use as photovoltaic power elements in nanoelectronics. Here we report the realization of p-type/intrinsic/n-type (p-i-n) coaxial silicon nanowire solar cells. Under one solar equivalent (1-sun) illumination, the p-i-n silicon nanowire elements yield a maximum power output of up to 200 pW per nanowire device and an apparent energy conversion efficiency of up to 3.4 per cent, with stable and improved efficiencies achievable at high-flux illuminations. Furthermore, we show that individual and interconnected silicon nanowire photovoltaic elements can serve as robust power sources to drive functional nanoelectronic sensors and logic gates. These coaxial silicon nanowire photovoltaic elements provide a new nanoscale test bed for studies of photoinduced energy/charge transport and artificial photosynthesis(10), and might find general usage as elements for powering ultralow-power electronics(11) and diverse nanosystems(12,13).