Current Status and Future Trends of Amorphous Silicon Solar Cells

The Kyoto Protocol for preventing global warming was adopted at the Conference of Parties III (COP3) of The United Nations Framework Convention on Climate Change held in Kyoto, Japan in December 1997. This Protocol established numerical targets for reducing greenhouse gas emissions in 2010 for each of the participating industrialized countries. In February 2005, the Kyoto Protocol was enacted and full-scale efforts began to reduce carbon dioxide (CO2) emissions, and subsequent efforts to introduce new energy having a low impact on the environment are expected to become invigorated. Among the types of new energy, photovoltaic power generation systems emit no CO2 while generating power, and their widespread use is highly anticipated. The Japanese government is promoting adoption of new energy by adopting: (1) measures involving power generation (q expanded adoption by the public sector, and w technical development to promote lower cost, higher efficiency, etc.) (2) measures involving heat (q comprehensive plans for local governments to introduce new forms of energy, w promotion of the Biomass Nippon Total Strategy, and e promotion of the introduction of biomass-derived fuel as transportation fuel, etc.) and other measures in order to achieve the projected level of adoption of new energy in 2010 as established by the Investigative Committee on Natural Resources and Energy. In particular, to achieve the goal of photovoltaic power generation of 4,820 MW by the year 2010, various assisting businesses (such as the Program for Infrastructural Development of Introduction of Residential PV System and Field Test Project on Photovoltaic Power Generation System for Industrial and Other Applications) and preferential governmental policies have accelerated the introduction of photovoltaic power generation. Moreover, the New Energy and Industrial Department Organization (NEDO Technical Development Organization), an independent administrative agency, has developed the “Photovoltaic Power Generation Roadmap for Year 2030 (PV2030)” which is a longterm strategy for technical development from 2004 through 2030. Here, it is assumed that by the 2030, photovoltaic power generation will provide approximately one-half of the electric power for household-use (approximately 100 GW as a photovoltaic power generating system), and therefore, technical innovation and system use have been studied in order to improve economic efficiency and to expand applicability. Meanwhile, the production of solar cells has increased dramatically since 1997, and the produced capacity of 288 MW in 2000 has undergone a more than 6.1-fold increase to 1,759 MW by 2005. Japan accounts for 833 MW or approximately 47 % of the total production quantity. Figure 1 shows the share of total solar cell production by country. Of the solar cells produced in 2005, crystalline silicon (Si) solar cells accounted for 84 %, and thin film Si accounted for approximately 14 %, but due to the problem of depletion of Si raw material, the share of amorphous silicon (a-Si) and CIS (copper-indium-selenium) solar cells is expected to increase. Fuji Electric began research and development on a-Si solar cells in 1978. In 1980, Fuji successfully developed and sold the world’s first commercial solar cells for use in calculators. Since 1980, Fuji has been contracted to perform research under the Sunshine Program administrated by the Agency of Industrial Science and Technology that belongs to the Japanese