Behind 2.0: The Back Enhanced Heterostructure with Interdigitated Contact Solar Cell Evolution

In this work we present the BEHIND 2.0 cell. The proposed back interdigitated amorphous/crystalline silicon heterostructure fabrication process has been exploited and simplified. We have fabricated rear junction, backside contact cells in which both the emitter and the back contact are formed by amorphous/crystalline silicon heterostructure, and the grid-less front surface is passivated by a double layer of amorphous silicon and silicon nitride, which also provides an anti-reflection coating. The entire self-aligned mask and photolithography-free process is performed at temperature below 300 °C with the aid of two metallic masks to create the interdigitated pattern, while the metallisation have been performed by screen-printing. We remark that the mask alignment is not critical since the n-type a-Si:H emitter width is three times wider than the p-type a-Si:H region. Initial results and modelling indicate that the intrinsic buffer layer plays a fundamental role in silicon surface passivation and isolation between the two contacts to enhance the cell open circuit voltage. The optimum buffer layer thickness has been evaluated to be 3.5 nm. Further the spacing between the two rear doped regions dramatically influences the photogenerated carrier collection, namely the fill factor. The modelling indicates that the best width spacing should shorter than 10 um. Finally the front surface passivation has been improved by particular SiNx films