Abstract
In this report we describe the essential problems and recent development of the solar energy conversion techniques. Photoenergy-conversion efficiency of silicon solar cell has been increased very much in recent years. In the laboratory scale, the efficiencies are, so far, more than 20% and 15% for single crystal and microcrystal silicon solar cells, respectively. Even with amorphous silicon solar cell, it exceeds more than 12%. Moreover the cost of silicon solar cell has been also lowered very much. When the expense of the generation of electricity becomes about 1$/W, the solar battery can compete with the present electricity system. It is expected to be achieved in 10 years with amorphous silicon.
The other solar cell system is a so-called photoelectrochemical cell composed of a semiconductor in electrolyte solution. Compared to the drastic progress in the silicon dry solar cell, the study of the wet cell system has been stagnant. Recently, however, noticeable results with photoelectrochemical cell were reported.One is the dye-sensitization system with ruthenium complex derivatives chemically attached on TiO2 surface. The solar energy conversion efficiency with that system against the AM (I) light exceeds about 8%. The other system is composed of d-band semiconductors such as pyrite (FeS2). The photocurrent is about 45mA/cm2, and it is very stable for more than six months. Drastic improvement of photoelectrochemical cell will be expected.
