n-type Hydrogenated Amorphous Silicon Oxide Containing a Microcrystalline Silicon Phase as an Intermediate Reflector in Thin-Film Silicon Solar Cells

摘要

To decrease the degree of degradation of a-Si:H/μc-Si:H tandem solar cells it is important to reduce the thickness of the a-Si:H component cell. A silicon oxide intermediate reflector between top and bottom cell reflects light back into the a-Si:H top cell and thus increases its photocurrent. Phosphorous doped silicon oxide films (a-SiO_x:H ) with a certain volume fraction of microcrystalline silicon (μc-Si:H ) are used for this purpose and the trade-off between the material's optical and electrical properties is studied in detail. Intermediate reflectors with different optical and electrical properties are used in tandem solar cells. The quantum efficiency and the reflectance of these solar cells are analyzed to find optical gains and losses due to the intermediate reflector. A suitable intermediate reflector is implemented in a tandem solar cell resulting in an increase in top cell current density by 1.3 mA/cm~2 with similar FF and V_(oc) compared to cells without intermediate reflector. A current 12.46 mA/cm~2 is achieved at a top cell absorber layer thickness of only 250 nm. A reduction of the a-Si:H top cell of about 40% for a stacked cell with intermediate reflector is possible while keeping the current of the device constant.