NOVELTY - A tandem junction photovoltaic device (40) comprises a top cell (40T) including a first n-type layer (49), an i-type layer (48) disposed in contiguous contact with the n-type layer, and a first p-type layer (47) disposed in contiguous contact with the i-type layer, where first n-type layer, i-type layer, and first p-type layer form an n-i-p diode; and a bottom cell (40B) comprising a second n-type layer (44) of n-type cadmium sulfide and a second p-type layer (43) of copper indium gallium diselenide (CIGS) disposed in contiguous contact with the second n-type layer.    USE - Tandem junction photovoltaic device i.e. monolithic tandem junction CIGS photovoltaic device, preferably monolithic tandem junction solar cell.    ADVANTAGE - High carrier collection, low processing temperature top cell is provided to achieve high efficiency monolithic tandem junction CIGS photovoltaic devices.    DETAILED DESCRIPTION - A tandem junction photovoltaic device (40) comprises a top cell (40T) including a first n-type layer (49), an i-type layer (48) disposed in contiguous contact with the n-type layer, and a first p-type layer (47) disposed in contiguous contact with the i-type layer, where first n-type layer, i-type layer, and first p-type layer form an n-i-p diode and have a band gap energy of approximately 1.7-1.75 eV; and a bottom cell (40B) comprising a second n-type layer (44) of n-type cadmium sulfide and a second p-type layer (43) of copper indium gallium diselenide disposed in contiguous contact with the second n-type layer, where bottom cell has a second band gap energy approximately 1.05-1.15 eV.    DESCRIPTION OF DRAWING(S) - The drawing is a schematic view showing a cell structure for a substrate configuration, monolithic tandem junction solar cell with n-i-p diode top cell and CIGS bottom cell.    Tandem junction photovoltaic device (40)    Bottom cell (40B)    Top cell (40T)    Second p-type layer (43)    Second n-type layer (44)    First p-type layer (47)    I-type layer (48)    First n-type layer (49)