NOVELTY - Solar cell (100) comprises: p-type layer (30); i-type amorphous silicon layer (32) layered over the p-type layer, and n-type silicon layer (34) layered over i-type amorphous silicon layer; where p-type layer comprises high-concentration amorphous silicon carbide layer (30a) doped with p-type dopant, a silicon layer (30b) formed at a side nearer to the i-type amorphous silicon layer than is the high-concentration amorphous silicon carbide layer and substantially not doped with the p-type dopant, and buffer layer (30c) formed between silicon layer and i-type amorphous silicon layer.    USE - As solar cell (claimed).    ADVANTAGE - The solar cell provides tandem-type solar cell having characteristic p-type layer included in a-Si (amorphous silicon) unit. The p-type layer formed over transparent conductive film includes amorphous silicon carbide layer in which absorption coefficient with respect to light of particular wavelength (such as 600 nm) changes with increase in thickness from transparent conductive film toward i-type layer. Because absorption coefficient of amorphous silicon carbide layer changes according to doping concentration of p-type dopant, doping concentration of p-type dopant is set to become higher as distance from i-type layer is increased. The doping concentration of p-type dopant can be stepwise or continuously increased as distance from i-type layer is increased. In case where doping concentration is to be stepwise increased, first, high-absorption amorphous silicon carbide layer doped with p-type dopant (such as boron) in first doping concentration is formed over transparent conductive film. Then, low-absorption amorphous silicon carbide layer doped with p-type dopant (such as boron) in second doping concentration lower than first doping concentration is formed over high-absorption amorphous silicon carbide layer. In addition, to adjust band gap and avoid influences of plasma during formation of i-type layer, buffer layer made of amorphous silicon carbide or microcrystalline silicon carbide is formed over low-absorption amorphous silicon carbide layer not doped with p-type dopant. During formation of layers by plasma chemical vapor deposition (CVD), it is preferable to temporarily stop plasma after low-absorption amorphous silicon carbide layer is formed, stop supply of p-type dopant-containing gas, adjust mixture ratios of mixture gas, pressure, and plasma generating high-frequency power, and then generate plasma again to stepwise form buffer layer. In this case, by stopping only plasma while maintaining supply of gas to transition from film formation of low-absorption amorphous silicon carbide layer to film formation of buffer layer, it is possible to prevent detachment of hydrogen from surface of low-absorption amorphous silicon carbide layer, and to reduce deficiency density at interface between low-absorption amorphous silicon carbide layer and buffer layer. With this configuration, open voltage (Voc) of solar cell can be improved. In addition, change of the doping concentration between doped low-absorption amorphous silicon carbide layer and non-doped buffer layer can be set to be abrupt. Alternatively, it is also possible to employ configuration where, in formation of buffer layer, after low-absorption amorphous silicon carbide layer is formed, transparent insulating substrate is moved to film formation chamber for forming i-type layer, and buffer layer is formed. In this manner, by forming buffer layer in film formation chamber to which p-type dopant-containing gas is not supplied, it is possible to set change of doping concentration between doped low-absorption amorphous silicon carbide layer and non-doped buffer layer to be abrupt, and to reduce deficiency density at interface between low-absorption amorphous silicon carbide layer and buffer layer. With such configuration, Voc of solar cell can be improved. Further, silicon layer not doped with p-type dopant is formed in condition where amorphous silicon layer or microcrystalline silicon layer is formed i.e. it is preferable to form silicon layer under condition where microcrystalline silicon is formed by adjusting mixture ratios of silicon-containing gas and the dilution gas (hydrogen). Alternatively, it is also possible to stepwise form silicon layer not doped with p-type dopant by temporarily stopping plasma after high-absorption amorphous silicon carbide layer is formed, adjusting mixture ratios of silicon-containing gas, carbon-containing gas, p-type dopant-containing gas, and dilution gas, pressure, and plasma generating high-frequency power, and then generating the plasma again. With this configuration, deficiency density which adversely affects power generation around interface of high-absorption amorphous silicon carbide layer and silicon layer not doped with the p-type dopant can be reduced. In addition, thickness of high-absorption amorphous silicon carbide layer which substantially becomes the p layer can be reduced. Therefore, Voc, short-circuit current density (Jsc), and fill factor (FF) of solar cell can be improved.    DETAILED DESCRIPTION - A solar cell (100) comprises: p-type layer (30); i-type amorphous silicon layer (32) layered over the p-type layer, and n-type silicon layer (34) layered over i-type amorphous silicon layer; where p-type layer comprises high-concentration amorphous silicon carbide layer (30a) doped with p-type dopant, a silicon layer (30b) formed at a side nearer to the i-type amorphous silicon layer than is the high-concentration amorphous silicon carbide layer and substantially not doped with the p-type dopant, and buffer layer (30c) formed between silicon layer and i-type amorphous silicon layer. The thickness of high-concentration amorphous silicon carbide layer is greater than thicknesses of silicon layer and buffer layer, or thickness of buffer layer is greater than thicknesses of silicon layer and high-concentration amorphous silicon carbide layer; and thickness of silicon layer is less than thicknesses of high-concentration amorphous silicon carbide layer and buffer layer. The buffer layer comprises silicon carbide, and silicon layer has lower concentration of carbon atoms than buffer layer or is substantially not doped with carbon atoms.    DESCRIPTION OF DRAWING(S) - The figures show structure of tandem-type solar cell and amorphous silicon (a-Si) unit of solar cells.    Transparent insulating substrate (10)    Transparent conductive film (12)    Intermediate layer (14)    Backside electrode layers (16, 18)    P-type layer (30)    High-absorption amorphous silicon carbide layer (30a)    Silicon layer substantially not doped with p-type dopant (30b)    Buffer layer (30c)    I-type layer (32)    N-type layer (34)    Tandem-type solar cell (100)    Amorphous silicon layer (102)    Microcrystalline silicon (104)