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The conversion of solar energy into electrical power is a demonstrated fact. The crucial considerations for this technology are: high conversion efficiency, long-term stability, and lower cost. In order for photovoltaics to make a significant contribution to global energy supply needs, it is essential that this technology be able to provide electricity at a cost that is competitive with the electricity generated by conventional means. The U.S. Department of Energy's (DOE) Photovoltaic Program objective is to develop this technology to a point where it can eventually become a viable energy option. One of the key elements of the program strategy is to carry out research and development on advanced and high risk materials and device concepts. DOE's research and development efforts are focused primarily on applied research for the development of promising new photovoltaic approaches, such as thin film and multijunction concepts, whereas basic research is directed toward gaining scientific knowledge in an effort to meet a recognized need. Further development of photovoltaic technology directs that knowledge towards the production of useful materials, devices, and systems. Despite the potentially high payoff of these research and development activities, they are costly, risky, and lengthy, and private enterprise is unlikely to pursue them for these reasons. The purpose of SERI's Photovoltaic Program is to conduct high risk, potentially high payoff research and development which will result in a scientific and technical knowledge base which private enterprise can use for further concept and product development and, ultimately, competitive application in electrical energy markets. Consistent with this strategy, a multiple research approach that ensures greater probability of success has been developed. In this paper we shall review the current status of research and development in a few leading technologies such as (i) amorphous silicon, (ii) polycrystalline thin films based on CuInSe2 and CdTe, (iii) high efficiency solar cells using III-V compounds and their alloys, and (iv) high efficiency crystalline silicon.
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