While organic/polymer solar cells have been the strong candidate for the new generation of photovoltaic technologies, one of the important aspects in realizing efficient and stable organic optoelectronic devices, such as organic/polymer solar cells and light emitting diodes, is the design of carrier transport layers between the organic active layer and metal electrodes. Among various materials available for carrier transport layers, metal oxides have great potential, owing to their excellent stability and wide range of energy level aligning capabilities. In this chapter, solution processed metal oxides and hybrid metal oxides for efficient carrier transport layers of organic optoelectronic devices will be described; these can contribute to achieving low-cost, large area and flexible organic photovoltaics.