TECHNOLOGY FOCUS - INORGANIC CHEMISTRY - Preferred Composition: The proportion of arsenic (As) in the group V material is 65% to 90% and the proportion of P in the group V material is 10% to 35%. Preferred Parameters: The GaAsP has a band gap in the range 1.6 to 1.8 eV. The nanostructure comprises a nanowire extending in a longitudinal direction, where the nanowire has a maximum transverse dimension less than 150 nm. Preferred Components: The GaAsP nanostructures comprise nanowires, each nanowire extending in a longitudinal direction from a surface of the substrate, the longitudinal direction being normal to the surface of the substrate. The silicon substrate comprises a first silicon layer having a first conductivity type; a second silicon layer having a second conductivity type, the first and second silicon layers being disposed to form the first p-n junction; and each GaAsP nanostructure having a core region surrounded by a shell region, the core region being formed from one of the first and second conductivity types and the shell region being formed from the other of the first and second conductivity types to form a second n-p junction. The photovoltaic cell comprises a third p-n junction between the first and second p-n junctions. The third p-n junction is formed in the silicon substrate or in each GaAsP nanostructure or at an interface. Preferred Method: In VLS method of growing a GaAsP nanostructure, the substrate is silicon and the method further comprises before subjecting the silicon oxide surface to Ga flux, etching holes in the silicon oxide surface layer to create an array of oxide free holes for receiving the Ga droplets in direct contact with the silicon. The proportion of P flux in the group V flux is initiated at a predetermined multiple of the proportion of P relative to the total amount of group V atoms to be present in the grown GaAsP nanostructure. The predetermined multiple is in the range of 0.1 to 6. The method comprises changing the proportion of P flux in the group V flux after forming the Ga droplets. The set growth temperature is greater than 570 Degrees C, and preferably higher than 600 Degrees C. Preferably, the growth temperature is in the range 620 Degrees C to 650 Degrees C and the V/III flux ratio is less than 120. The method comprises selecting the predetermined multiple based on the growth temperature, the V/III flux ratio and the ratio of the number of P atoms in P molecules in the P flux to the number of As atoms in As molecules in the As flux. It further comprises forming a silicon oxide layer on the substrate before subjecting it to the Ga flux; and doping the nanostructure. Doping comprises introducing a dopant flux during growth; or doping comprises overgrowing each nanostructure with a doped GaAsP shell after the nanostructure is grown.