Self-sacrifice alkali acetate seed layer for efficient four-terminal perovskite/silicon tandem solar cells

Seed-assisted growth is an effective way to achieve high-quality perovskite active layers for efficient and stable perovskite solar cells (PSCs). However, it is still challenging for conventional seed layers to realize the synergistic effect of the perovskite crystallization control and defect passivation without hindering the charge extraction and light absorption. Here, a self-sacrifice alkali acetate seed layer is employed at the buried perovskite interface to assist a vertical bottom–top growth of the high-quality perovskite film. Meanwhile, the dissolved alkali and acetate ions can diffuse into the perovskite layer, providing an efficient defect passivation and a favorable interfacial energy band alignment at both electron- and hole-selective contacts. As a result, these favorable synergistic effects enable the fabrication of a 21.69 % efficient PSC with a boosted fill factor of 83.33 % and enhanced long-term stability. Moreover, the optimized semitransparent perovskite solar cell (ST-PSC) achieves a certified efficiency of 19.28 %, the highest reported for p – i – n typed ST-PSCs. Combining the ST-PSC with a silicon bottom cell, the four-terminal perovskite/silicon tandem solar cell reaches a record efficiency of 28.28 %. Self-sacrifice alkali acetate seed layer for efficient four-terminal perovskite/silicon tandem solar cells. • A bottom-up perovskite crystallization is assisted by a self-sacrifice seed layer. • The dissolved seed layer provides efficient passivation contacts at both interfaces. • The highest efficiency of 19.28 % among p – i – n typed semitransparent perovskite cells. • The 4-T perovskite/silicon tandem cell produces an efficiency of 28.28 %.