Self-Aligned Silica Nanoparticle Rear Reflectors for Single-Junction Si and Perovskite-Si Tandem Solar Cells

Infrared light management is crucial to maximize the optical performance of crystalline Si-based single junction and tandem solar cells. For this end, a low refractive index dielectric is typically inserted under the rear metal and an electrical contact is obtained locally through the dielectric. However, the realization of such an architecture can require numerous fabrication steps that are time and resource intensive. Herein, a simple approach is proposed in which commercially available, low-cost SiO₂ nanoparticles (NPs) are spin coated as rear reflectors on pyramid-textured Si, leaving the pyramid tips locally exposed for direct contact by an electrode without additional patterning. In Si heterojunction solar cells, complementing a 40 nm-thick indium tin oxide (ITO) layer with the SiO₂-NPs yields a gain of 0.3 mA cm⁻² in short-circuit current density compared to that obtained with a bare, 100 nm-thick ITO layer. Combined with reduced electrical losses, power conversion efficiency gains of 0.5%_abs to 0.3%_abs for single junction Si and perovskite-Si tandem cells are demonstrated, respectively. Finally, it is shown that the NPs can also be processed on large areas via blade coating and that the process can be further simplified by a change in the fabrication sequence of the SiO₂-NP and ITO layers.