Optimization of doped bottom cell layers for industrial micromorph tandem modules

This work reports on the optimization of amorphous-microcrystalline silicon tandem solar cells and modules on LPCVD ZnO on 1.4m² substrate size. The focus is on the optimization of PECVD deposition of n-and p-type doped layers for the microcrystalline silicon bottom cell deposited in a commercially available Oerlikon Solar KAI PECVD system. For this type of layers, both electro-optical properties with respect to cell and module efficiency as well as deposition rate with respect to throughput are of interest. A novel silicon oxide based n-layer which enhances current density of the solar cell by reducing absorption loss was introduced in the bottom cell design. An appropriate optimization of the n-layer was found crucial to achieve a suitable device performance. In a second step, the increase of the deposition rate of the n-and p-layers was addressed to match the throughput requirements for an industrial low cost production process.