We present a method for determining the voltage and current loss in solar cells using the modulation capacitance voltage measuring technique. Both losses can be investigated in the forward biased mode and the generator mode. The method is especially suitable for characterising: particular loss components due to band offsets and interface recombination in heteroemitter solar cells. Nonlinear loss-versus-current characteristics were generally found for a-Si:H(p(+)), SIPOS(n(+)) and ZnO(n(+)) emitters on c-Si. The losses are strongly modified by the preparation which affects the heterojunction interface. These results can give insight into effects of recombination and band offsets in both bands. PACS. 84.60.Jt; 73.40.Lg; 73.50.Gr; 73.40.-c.