A sunlight irradiation strategy was developed for the synthesis of concave gold nanoplates in the presence of polydiallyl dimethyl ammonium chloride (PDDA) as the capping agent. Apart from the role of stabilizer, PDDA plays the role of a shape directing agent as well as an oxidative etchant in conjunction with dissolved oxygen. The edge length of the nanoplates was determined to be about 15 μm, and atomic force microscopy investigations proved that the nanoplates are concave, with thickness at the centre being about 10 nm. X-ray diffraction studies and selected area electron diffraction investigations confirmed that the nanoplates are bound by the {111} plane. The nanoplates were also characterized by energy-dispersive X-ray analysis and X-ray photoelectron spectroscopy.