Two-dimensional (2D) InSe and WS2 exhibit promising characteristics for optoelectronic applications.However,they both have poor absorption of visible light due to wide bandgaps:2D InSe has high electron mobility but low hole mobility,while 2D WS2 is on the contrary.We propose a 2D heterostructure composed of their monolayers as a solution to both problems.Our first-principles calculations show that the heterostructure has a type-Ⅱband alignment as expected.Consequently,the bandgap of the heterostructure is reduced to 2.19eV,which is much smaller than those of the monolayers.The reduction in bandgap leads to a considerable enhancement of the visible-light absorption,such as about fivefold (threefold) increase in comparison to monolayer InSe (WS2)at the wavelength of 490nm.Meanwhile,the type-Ⅱ band alignment also facilitates the spatial separation of photogenerated electron-hole pairs;i.e.,electrons (holes) reside preferably in the InSe (WS2) layer.As a result,the two layers complement each other in carrier mobilities of the heterostructure:the photogenerated electrons and holes inherit the large mobilities from the InSe and WS2 monolayers,respectively.