To understand the influence of proton irradiation on lattice-matched GaInP/GaAs/Ge triple junction (TJ) solar cells under low intensity, low temperature (LILT) conditions, we investigated electrical behaviors of top, middle, and bottom component cells together with TJ cells under these conditions. Proton irradiations with energies of 1 MeV and fluences ranging from 2 × 10 10 to 1.6 × 10 12 cm −2 were performed at temperatures ranging from 100 to 300 K. Our study reveals that any of the 3 subcells can become the current limiting cell in the TJ cell, depending on temperature and fluence. In particular, remarkable degradation of the bottom cell at low temperature can make this subcell the current limiting in a TJ cell even for limited fluences. The results indicate that the defect distribution is non-uniform for low temperature irradiation.