Oxide semiconductor nanowire (NW) suspension based devices have been attracted growing interest in smart window applications due to their great controllability of light transmittance, simplicity and long term stability. Recently, we demonstrated smart window device using the suspension of electrospun TiO2 or solvothermally synthesized ZnO NWs in viscous polydimethylsiloxane (PDMS) matrix. The operating principle of the oxide semiconductor NW and PDMS device is based on the alterable orientation, alignment or spatial distribution of the NWs in an electric field, by changing light scattering cross-section and thus reversibly increasing or decreasing transmittance [1]. One-dimensional (1D) nanostructures such as NWs exhibit a good response to electric field due to the highly anisotropic shape. Herein we report transition metal doped ZnO NW and PDMS based smart window devices. Doping ZnO NWs with other chosen metal ions, such as transition metals, may lead to the emergence of new targeted material properties. For instance, high quality ZnO nanocrystals doped with transition metal cations lead to enhanced optical absorption of light in visible range. The pristine ZnO NWs used in our previous work did not exhibit visible light absorption and transmittance of ZnO NWs and PDMS based smart window device was regulated by changing scattering cross-section. The visible light absorption could increase efficiency of smart window device, because during electrophoretic alignment of NWs towards direction of electric field will change not only scattering, but also visible light absorption cross-section. One-dimensional ZnO nanostructures have been synthesized by wet chemical techniques including microemulsion hydrothermal synthesis, surfactant-assisted hydrothermal orientation growth and alcohol solution refluxing. However, synthesis of high quality transition metal doped ZnO nanowires with small diameter and high aspect ratio is still a challenge. Most wet chemical methods fail to produce high aspect ratio doped ZnO NWs in large quantities. Here we are demonstrating large-scale, single-step, direct solvothermal method and have successfully prepared high aspect ratio single crystalline transition metal (Co, Cu, Fe, Ni, Mn) doped ZnO NWs. The solvothermal synthesis process presented here can be scaled up to macro scale production and the fact that NWs need no further modification increases the technological potential of oxide semiconductor nanowire suspension based devices electro-optical smart window devices.