We have obtained the world's highest total area conversion efficiency of 11.1% for a 100cm2 integrated-type single-junction a-Si solar cell submodule. This was achieved by the development of various advanced technologies, such as a new ultra-thin i/n interface layer and a new laser patterning method using an ablation phenomenon.
To acheive further improvement in the conversion efficiency of a-Si based solar cells, we focus on polycrystalline silicon (poly-Si) thin-film for a-Si/poly-Si tandem solar cells. As far as material technology is concerned, we have used a new solid phase crystallization (SPC) method from amorphous silicon (a-Si) films deposited by plasma-CVD. The maximum mobility of 623 cm2/V.s was achieved on textured substrates at a carrier concentration of 3.0 × 1015 cm-3. This film has been applied to the active layer of poly-Si solar cells on metal substrates and a conversion efficiency of 6.2% has been obtained with poly-Si film of 12 μm thickness made by SPC at 600°C.
In the field of device technology, we have developed new artificially constructed junction (ACJ) solar cells using p-type a-Si/i-type a-Si/n-type crystalline silicon (c-Si). We call this a HIT (Heterojunction with Intrinsic Ihin-layer) structure, and we have achieved a conversion efficiency of 18.1% for this type of solar cells. This is the highest reported value for a cell with a junction fabricated at low temperature (∼ 120°C).