Intrinsic and extrinsic defects around the p-n interface in Cu2SnS3 (CTS) solar cells were evaluated using low-temperature photoluminescence (LT-PL) measurements. The intrinsic defects were investigated based on the PL-dependence of CTS films on the excitation power and temperature. Donor-acceptor pair recombination was observed with shallow acceptors (copper vacancies, V Cu) located approximately 18 meV above the valence band maximum and typical donors located 72 and 112 meV below the conduction band minimum (CBM). The PL spectra of various CTS solar cell structures were measured to identify the Cd-related defects formed by Cd diffusion from the CdS layer. A new LT-PL peak was observed at 0.87 eV for the CdS/CTS solar cells, corresponding to D-A pair recombination with Cd on Cu site donors located 62 meV below the CBM. A p-n homojunction may form in CTS by V Cu passivation by Cd diffusion and suppressed interface recombination.