A metal chalcogenide composite nano-particle comprising a metal capable of
forming p-type semiconducting chalcogenide nano-particles and a metal
capable of forming n-type semiconducting chalcogenide nano-particles,
wherein at least one of the metal chalcogenides has a band-gap between
1.0 and 2.9 eV and the concentration of the metal capable of forming
p-type semiconducting chalcogenide nano-particles is at least 5 atomic
percent of the metal and is less than 50 atomic percent of the metal; a
dispersion thereof; a layer comprising the nano-particles; and a
photovoltaic device comprising the layer.