Down-conversion is a feasible way to improve conversion efficiency of silicon solar cell. However, the width of excitation band for down-converter based on trivalent lanthanide ions is still not satisfying. Here, we designed and fabricated a heterostructural down-converter composed of Y₂O₃: [(Tb³⁺-Yb³⁺), Li⁺] quantum cutting phosphor and ZnSe. The ZnSe phase was used to absorb the incident light with energy larger than its bandgap, and transfer the energy to Tb³⁺-Yb³⁺ quantum cutting couple. Short-wavelength incident light was finally converted into a strong Yb³⁺ emission at about 1000 nm, locating at the maximal spectral response of silicon solar cell. The excitation band of the down-conversion covers a wide region of 250-550 nm. Benefiting from the energy match between ZnSe bandgap and ⁷F₆→⁵D₄ absorption of Tb³⁺ ions, the bandwidth of down-conversion is almost maximized.