NOVELTY - The multijunction photovoltaic cell (10) or solar cell system comprises an aluminum indium phosphide (AlInP) top subcell window layer, a gallium indium phosphide (GaInP) top subcell emitter layer disposed below the window layer, a gallium indium phosphide (GaInP) top subcell base layer disposed below the emitter layer, an aluminum gallium indium phosphide (AlGaInP) or aluminum gallium arsenide (AlGaAs) top subcell back-surface field (BSF) layer disposed below the top subcell base layer, and a tunnel junction comprising a GaInP tunnel junction layer disposed below the top subcell BSF layer.    USE - The multijunction photovoltaic cell or solar cell system such as a GaInP/GaInAs/GaInNAs/Ge 4-junction cell, a thin GaInP/thick GaInPAs/GaInAs/Ge 4-junction cell and a thin GaInP/thick GaInPAs/GaInAs/GaInNAs/Ge 5-junction cell is useful in a satellite system (all claimed).    ADVANTAGE - The multijunction photovoltaic cell or solar cell system can be economically manufactured with increased conversion efficiency, high current density, and improved performance, lifespan and mechanical strength.    DETAILED DESCRIPTION - The multijunction photovoltaic cell (10) or solar cell system comprises an aluminum indium phosphide (AlInP) top subcell window layer, a gallium indium phosphide (GaInP) top subcell emitter layer disposed below the window layer, a gallium indium phosphide (GaInP) top subcell base layer disposed below the emitter layer, an aluminum gallium indium phosphide (AlGaInP) or aluminum gallium arsenide (AlGaAs) top subcell back-surface field (BSF) layer disposed below the top subcell base layer, a tunnel junction comprising a GaInP tunnel junction layer disposed below the top subcell BSF layer, a GaInP middle subcell window layer disposed below the tunnel junction that is disposed below the top subcell BSF layer, a gallium indium arsenide (GaInAs) middle subcell emitter layer disposed below the middle subcell window layer, a GaInAs middle subcell base layer disposed below the GaInAs middle subcell emitter layer, a GaInP or AlGaAs BSF layer disposed below the GaInAs middle subcell base layer, a tunnel junction comprising a GaInAs tunnel junction layer disposed below the middle subcell BSF layer, a GaInAs buffer layer disposed below the tunnel junction that is disposed below the middle subcell BSF layer, a GaInP nucleation layer and bottom subcell window layer disposed below the GaInAs buffer layer, a germanium (Ge) bottom subcell emitter layer disposed below the GaInP nucleation layer and bottom subcell window layer, a Ge bottom subcell base layer and high-miscut-angle substrate disposed below the Ge bottom subcell emitter layer, a heavily-doped cap contacting layer disposed above the AlInP top subcell window layer, a metal contact disposed above the heavily-doped cap contacting layer, a metal contact disposed below the Ge bottom subcell base and substrate layer, an additional AlInP middle subcell window layer disposed between the tunnel junction that is below the top subcell BSF layer and the GalnP middle subcell window layer, a GaInP middle subcell heterojunction emitter layer disposed between the tunnel junction disposed below the top subcell BSF layer and the GaInAs middle subcell base layer, a Ge substrate comprising a surface misoriented from a (100) plane by an angle of 8-40 degrees toward a nearest (111) plane, subcells (20, 40, 60) of GaInP/GaInAs/gallium indium nitrogen arsenide (GaInNAs), thin GaInP/thick aluminum indium phosphorus arsenide (GaInPAs)/GaInAs and thin GaInP/thick GaInPAs/GaInAs/GaInNAs disposed above the Ge substrate, a solar array having solar cell. INDEPENDENT CLAIMS are included for:    (1) an optoelectronic device;    (2) a satellite system;    (3) a method for increasing a GaInP top subcell bandgap;    (4) a method for producing a GaInP top subcell with a high bandgap;    (5) a method for increasing a conversion efficiency in a solar cell; and    (6) a method for increasing a doping and a growth rate on a III-V device.    DESCRIPTION OF DRAWING(S) - The diagram shows a cross-sectional view of a 3-junction photovoltaic cell.    Multijunction photovoltaic cell (10)    Anti-reflection coating (16)    Subcells (20, 40, 60)    Germanium base layer (64)    Back metal contact. (68)