Chao Zhang, Matthias Meier, Wendi Zhang - Influence of Interface Textures on Light Management in Thin-Film Silicon Solar Cells With Intermediate Reflector

THIN-FILM silicon tandem solar cells based on a hydrogenated amorphous top and a microcrystalline bottom cell are well investigated and an industrially applied technology. A challenge of this type of solar cells is the light-induced degradation of material and the associated deterioration of the electrical properties known as the Staebler– Wronski effect. To minimize the resulting efficiency loss, it is beneficial to reduce the thickness of the top cell. Since both subcells are connected in series, the subcell with the lowest current density limits the total current density of the whole device. A strategy to maintain a high current density, even with thinner top cell absorber layers, is to introduce an intermediate reflector layer (IRL) made of microcrystalline silicon oxide between the top and bottom cell. This additional layer has a lower refractive index compared with silicon and reflects a part of the incident light back into the top cell. Thereby, the current of the top cell and the bottom cell can be matched despite the reduced thickness of the top solar cell. A lot of study has been accomplished on the texture and thickness related effectiveness of an IRL. Detailed investigations have been made applying periodic and randomly textured interfaces. Some precise predictions on the impact of a thickness variation of the IRL on the top and bottom cell current focusing on the low pressure chemical vapor deposition (LPCVD) texture are shown in. While other groups focused on finding an optimal thickness of the IRL and its impact on light kept in the top cell, the emphasis in our contribution is on the impact of a large range of different textures applying only one single thickness for the IRL on all samples.