The capability to design innovative semiconductor materials with desirable functionalities is a highly challenging task. In this talk, we give a brief overview of our recent progresses in designing semiconductormetal oxidesmaterials for photoelectrochemical energy conversionincluding photocatalytic solar fuel generation and low cost solar cells.In more details, we have been focusingonthe following a few aspects; 1)band-gap engineering of layered semiconductor compoundsincluding layered titanate, tantalate and niobate-based metal oxide compoundsforvisiblelight phtocatalysis, and2)two-dimensionalnanosheets/nanoplates of TiO2, Fe2O3and WO3as building blocks for new photoelectrode design，and 3) the design of semiconductor nanoparticles for low cost solar cells including perovskite solar cell applications.1-5The resultant material systems exhibited efficient visible light photocatalytic performanceand improved power conversionefficiencyin solar energy,which underpin important solar-energy conversion applications includingsolar electricity and solar fuel production.