We present back-contacted amorphous/crystalline silicon heterojunction solar cells (IBC-SHJ) on n-type substrates with fill factors exceeding 78% and high current densities, the latter enabled by a SiNx /SiO2 passivated phosphorus-diffused front surface field. Voc calculations based on carrier lifetime data of reference samples indicate that for the IBC architecture and the given amorphous silicon layer qualities an emitter buffer layer is crucial to reach a high Voc, as known for both-side contacted silicon heterojunction solar cells. A back surface field buffer layer has a minor influence. We observe a boost in solar cell Voc of 40 mV and a simultaneous fill factor reduction introducing the buffer layer. The aperture-area efficiency increases from 19.8 ± 0.4% to 20.2 ± 0.4%. Both, efficiencies and fill factors constitute a significant improvement over previously reported values. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) In this Letter, back-contacted amorphous/crystalline silicon heterojunction solar cells with good fill factors and high current values are presented. Aperture solar cell efficiencies up to 20.2±0.4% are measured, demonstrating the functionality of this cell architecture. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.