Novel materials must be found in order to develop advanced sustainable solar energy technologies. This paper presents recent research being pursued by my group at Arizona State University in the study and development of III-V semiconductors for improving the efficiency of photovoltaic devices beyond the Shockley-Queisser limit. Although in the early stages of development, significant advances are happening in two directions described here. One is for intermediate-band solar cells, using InAs quantum dots in wide gap III-V semiconductor thin films. The other is for double-junction InGaN solar cells for high-temperature applications. The theoretical efficiencies of these two system resemble that of triple-junction cells, at above 60%.