We present a model that takes into account the interface-defects contribution to the binding energy of charged excitons (trions). We use Gaussian defect potentials and one-particle Gaussian basis set. All the Hamiltonian defect terms are analytically calculated for the s-like trial wave functions. The dependence of the binding energy and of the trion size on the quantum-well width and on the defect size are investigated using a variational method for GaAs/Al0.3Ga0.7As quantum wells. We show that even in the case of strictly structural defects the trion is more strongly affected than the exciton.6511