TECHNOLOGY FOCUS - MECHANICAL ENGINEERING - Preferred Device: In the tandem solar cell device, the alloy layer further comprising a p-type impurity with high doping concentration. The material of the substrate can be silicon, germanium, Si-Ge, Ga-arsenic (As) or indium phosphide (InP). The tandem solar cell device further comprises a buffer layer formed between the substrate and the first tunnel junction. The material of the buffer layer, the heavily doped n-type layer of the first tunnel junction, the alloy layer of the first tunnel junction and the first p-n junction contains one or more elements selected from gallium, aluminum, indium, arsenic, phosphorus, nitrogen and silicon. The element with atomic number larger than that of gallium can be selected from indium, thallium, antimony, bismuth, tin, lead, polonium, cadmium, and mercury. The concentration of the element with atomic number larger than that of gallium can be 1-2%, which is equal to 3.5x1021-1.7x1022 (1/cm3). The tandem solar cell device also comprises a second tunnel junction formed on the first p-n junction where the second tunnel junction having a heavily doped n-type layer and an alloy layer where the alloy layer having an element with atomic number larger than that of gallium; and a second p-n junction formed on the second tunnel junction. The material of the heavily doped n-type layer of the second tunnel junction, the alloy layer of the second tunnel junction and the second p-n junction contains one or more elements selected from gallium, aluminum, indium, arsenic, phosphorus, nitrogen and silicon. Moreover, the tandem solar cell device comprises a set of tunnel junction with alloy layer having an element with atomic number larger than that of gallium and a set of p-n junction repeated formed on the second p-n junction separately. Preferred Method: Manufacturing the tandem solar cell device further comprises forming a set of tunnel junction with alloy layer having an element with atomic number larger than that of gallium and a set of p-n junction repeated on the p-n junction separately. The differences in lattice of the tunnel junction with the substrate or the p-n junction is reduced by forming the alloy layer.