Interdigitated back-contacted silicon heterojunction solar cells with improved fill-factor and efficiency

We present back-contacted amorphous/crystalline silicon heterojunction solar cells (IBC-SHJ) with a contact system leading to fill factors up to 78.8% and high current densities, the latter enabled by classical high temperature processing techniques. Conversion efficiencies of up to 20.2±0.4% are reached which constitutes an improvement of over 4% absolute with respect to previously reported results of this cell type. In contrast to previous IBC-SHJ architectures a high quality dielectric passivation layer between the amorphous silicon layers is introduced, allowing for the metallization of the entire active emitter area, and therefore eliminating an important loss mechanism for the fill-factor. We compare solar cells with and without a buffer layer of intrinsic amorphous silicon at the emitter consisting of p-doped amorphous silicon. We find that the inclusion of a buffer layer reduces the fill-factor by about 3% absolute to 75.7% for the best cell (η=20.2%). At the same time the V
_oc
increases by 40mV to 673mV. The difference in V
_oc
can be attributed to recombination at the emitter junction, since the short circuit currents of both cells are equal. Calculating the V
_oc
based on photoconductance decay measurements on reference structures, we find that the values measured in illuminated I-V-measurements lack behind the potential of the layers by 10...20mV. Moreover we study the performance of different scenarios of contact separation on the rear side which would allow simplified fabrication of interdigitated back-contacted heterojunction solar cells.