High Efficiency Perovskite‐Silicon Tandem Solar Cells: Effect of Surface Coating versus Bulk Incorporation of 2D Perovskite

TLDR

Mixed‑dimensional perovskite solar cells combining 3D and 2D perovskites have attracted interest for their improved efficiency and stability, yet the optimal method to combine them remains unclear. The study investigates surface coating versus bulk incorporation of 2D perovskites into a 3D perovskite to determine the superior approach. The authors compare surface coating and bulk incorporation by applying different aliphatic alkylammonium bulky cations to the 3D perovskite. Surface coating with bulky cations forms a quasi‑2D perovskite phase that passivates defects and boosts performance, whereas bulk incorporation creates a pure 2D phase that degrades crystallinity and reduces efficiency; using n‑butylammonium bromide surface coating in a four‑terminal tandem with silicon yields 27.7 % efficiency in a size‑matched configuration.

Abstract

Abstract Mixed‐dimensional perovskite solar cells combining 3D and 2D perovskites have recently attracted wide interest owing to improved device efficiency and stability. Yet, it remains unclear which method of combining 3D and 2D perovskites works best to obtain a mixed‐dimensional system with the advantages of both types. To address this, different strategies of combining 2D perovskites with a 3D perovskite are investigated, namely surface coating and bulk incorporation. It is found that through surface coating with different aliphatic alkylammonium bulky cations, a Ruddlesden–Popper “quasi‐2D” perovskite phase is formed on the surface of the 3D perovskite that passivates the surface defects and significantly improves the device performance. In contrast, incorporating those bulky cations into the bulk induces the formation of the pure 2D perovskite phase throughout the bulk of the 3D perovskite, which negatively affects the crystallinity and electronic structure of the 3D perovskite framework and reduces the device performance. Using the surface‐coating strategy with n ‐butylammonium bromide to fabricate semitransparent perovskite cells and combining with silicon cells in four‐terminal tandem configuration, 27.7% tandem efficiency with interdigitated back contact silicon bottom cells (size‐unmatched) and 26.2% with passivated emitter with rear locally diffused silicon bottom cells is achieved in a 1 cm 2 size‐matched tandem.