Nanocrystalline silicon oxide interlayer in monolithic perovskite/silicon heterojunction tandem solar cells with total current density >39 mA/cm2

Silicon heterojunction solar cells are implemented as bottom cells in monolithic perovskite/silicon tandem solar cells. Commonly they are processed with a smooth front side to facilitate wet processing of the lead-halide perovskite cell on top. The inherent drawback of this design, namely, enhanced reflection of the cell, can be significantly reduced by replacing the amorphous or nanocrystalline silicon front side n layer of the silicon cell by a nanocrystalline silicon oxide n layer. It is deposited with the same commonly used plasma-enhanced chemical vapor deposition and can be tuned to feature opto-electrical properties for enhanced light coupling into the Si bottom cell, namely, low parasitic absorption and an intermediate refractive index of ~2.6. We demonstrate that a 80 - 100 nm thick layer results in 0.9 mA/cm
²
current gain in the bottom cell yielding tandem cells with a top cell + bottom cell total current above 39 mA/cm
²
. These first nc-SiO
_x
:H-coupled tandem cells reach an efficiency >23.5 %.