Coated conductor wire using superconducting Rare-earth-Ba2Cu3O7-x is a technology capable of producing many exciting new and improved devices, with applications from MRI magnets to fusion power plants. However, to be successfully commercialised the cost of performance of the wires must be improved. This thesis investigates a new method of producing high quality REBa2Cu3O7-x films at fast rates which could help reduce costs and increase production capacity. In particular two liquid-assisted processing methods, which use a liquid phase during growth stages to increase diffusion, for REBa2Cu3O7-x production are examined. First a new method which uses a non-stoichiometric composition to generate a liquid phase during REBa2Cu3O7-x deposition stages is demonstrated. We show it is possible to produce YBa2Cu3O7-x films at fast rates which have similar performance to stoichiometric films grown ten times slower. We also show it is possible to improve the performance of the liquid-assisted films via selective doping with secondary phases such as Ba2YNbO6 and by using a mixed rare-earth content, therefore producing not only YBa2Cu3O7-x at fast rates but also with an optimised pinning microstructure. A second method in which a liquid phase is formed, and REBa2Cu3O7-x growth occurs, after the deposition stage, is also investigated. This method is currently used industrially by SuNAM Co. Ltd., a collaborator on this project. We show that it is possible to replicate the liquid-assisted process used at the factory via pulsed laser deposition in a vacuum chamber. We use these results to investigate the effect doping the liquid-assisted composition with platinum and cerium oxide has on the formation of large, and unwanted, Gd2O3 particles in the liquid-assisted films. Overall we show that it is possible to create superconducting REBa2Cu3O7-x films at fast growth rates while also optimising the microstructures to create the strongest performance across a range of temperature and magnetic field conditions. This work has already led to two papers and a patent sponsored by a coated conductor manufacturer.