Modification of Sub-Micron Pyramid Texturing on Crystalline Silicon for Tandem Solar Cells

Crystalline silicon (<i>c</i>-Si) solar cells, due to their suitable bandgap of 1.1 eV, high open circuit voltage of up to 750 mV, and mature technology, are considered the leading candidate for the bottom cell in tandem configurations. However, <i>c</i>-Si bottom cells often exhibit lower current density than high band-gap top cells, such as perovskite and organic solar cells, which significantly reduces overall efficiency due to current mismatch.<br/><br/>To overcome this intrinsic drawback, surface texturing technology, particularly pyramid texturing, can be employed. Pyramid texturing is a commonly used method to improve the current density of <i>c</i>-Si solar cells. This technique typically utilizes pyramids with sizes of 3 to 5 µm. However, this structure is difficult to stack due to the thickness of emerging thin-film solar cells produced by solution fabrication processes, which is much lower than the 3-5 µm pyramid structure.<br/><br/>Since most thin-film based top solar cells for tandems are fabricated through solution processes, stacking these top cells requires <i>c</i>-Si surface structures with moderate heights of less than 1 µm. In this study, we investigated the optimal structure size through simulation, aiming for low reflectance on the front surface of <i>c</i>-Si solar cells while accommodating the integration of top cells. By adjusting key factors of the surface texturing process—such as etchant concentration, etching time, etching temperature, and additives—we modified the size and uniformity of the pyramid structures on the silicon surface.<br/><br/>The resulting pyramid structures exhibited a uniform height of 1.0-1.3 µm, lower than the conventional 3-5 µm height, and achieved a reflectance of 12.5%, which was significantly lower than the 44.9% reflectance of planar silicon surfaces. This outcome demonstrates the feasibility of producing structures that can be covered by the thickness of solution-processed top cells, highlighting the potential for efficiency enhancement in <i>c</i>-Si-based tandem solar cells.