NOVELTY - The photovoltaic device (200A,200B) has lower pn junction layers (210) comprising silicon, and upper pn junction layers formed over the lower pn junction layers. The upper pn junction layers comprise a cadmium telluride (CdTe) layer (240), and are electrically serially connected to the lower pn junction layers. The upper pn junction layers convert a first portion of photons into a first electric voltage. The lower pn junction layers convert a second portion of photons into a second electric voltage lower than the first electric voltage.    USE - Multi-junction photovoltaic device used in photovoltaic module (claimed) used for fabrication of photovoltaic solar cells.    ADVANTAGE - Provides higher voltage and higher light conversion efficiency compared to conventional silicon photovoltaic cells, and increases solar cell efficiency. The multi-junction photovoltaic device includes two stacked solar cells having different band gap energies, the top solar cell capturing shorter wavelength photons and allows the longer wavelength photons to pass through and the lower solar cell capturing the longer wavelength photons and converting them into electric current. The photovoltaic device has higher total efficiency because it can convert photons in a wider spectral range into electricity and minimize the voltage loss for a single junction solar cell. More electric energy can be produced from the same amount of photons, i.e. the output power per unit area is increased compared to conventional silicon based photovoltaic devices.    DETAILED DESCRIPTION - The upper pn junction layers comprise a semiconductor layer (250) in contact with the CdTe layer. The semiconductor layer comprises cadmium sulfide or zinc sulfide. The CdTe layer is doped with copper, chlorine, or extra cadmium. INDEPENDENT CLAIMS are also included for the following:    (1) a photovoltaic module; and    (2) a method for forming a multi-junction photovoltaic device.    DESCRIPTION OF DRAWING(S) - The drawing shows the cross-sectional view of a multi junction photovoltaic module consisting of electrically serially connected multi junction photovoltaic cells.    Photovoltaic devices (200A,200B)    Lower pn junction layers (210)    Layer (240)    Semiconductor layer (250)    Multi- junction photovoltaic module (300)